Leather auxiliaries
I. INTRODUCTION
Organic Chemistry can generally be defined as the chemistry of carbon compounds. This; It depends on the carbon atom's ability to bond more than the other elements among 109 known elements. Because carbon, unlike other atoms, creates bonds by sharing electrons instead of electrons or electrons. Also, since a carbon atom can make four bonds, it can easily bond with other carbon atoms and with other atoms. For this reason, there are more than 8 million known compounds of carbon today and new ones are added to them every year. While some of these compounds are obtained naturally, some are obtained by synthesis in laboratories. Although many of the carbon compounds are considered organic structure,
The chemical compounds have been divided into two classes, namely "Inorganic" and "Organic", depending on the source and their structure from which they were obtained. Inorganic compounds are provided from minerals, organic compounds are obtained from vegetable and animal sources (living structures). But; The fact that organic structures obtained from live sources can be synthesized in laboratories today has caused this idea to change slowly. However; This distinction between organic and inorganic compounds continues today.
Starting from an inorganic structure, the first you-thesis of an organic compound in a laboratory environment was performed by F. Wöhler in 1828. Searching; showed that a urea compound can be obtained artificially by heating the inorganic structure, ammonium cyanate.
HE IS
heat ||
NH 4 NCO H 2 N-C-NH 2 Ammonium cyanate Urea
Today, while many organic compounds are obtained from vegetable and animal sources, many compounds are produced by synthesis. In some of these synthesis reactions, inorganic structures can be used as starting materials, while many remaining compounds are generally obtained from organic starting materials that can be divided into two main classes. The first of these sources is oil and coal. Another important group includes wood and agricultural materials.
Based on this source of raw materials, it is possible to synthesize compounds made up of thousands of carbon atoms and even thousands of ring structures with members in different numbers. The main atoms that can be attached to carbon atoms in the mentioned chain and ring structures are; hydrogen, oxygen, sulfur, nitrogen, fluorine, chlorine, bromine, iodine and phosphorus.
Each different arrangement of atoms in an organic molecule leads to the formation of a different compound. Each of the compounds produced exhibit different physical and chemical properties. Therefore, one of the main problems of organic chemistry is to reveal how the atoms in molecules are arranged, that is, to illuminate the structure of the molecule. Another important problem is to investigate how the reactions take place and to clarify their mechanisms.
Today, organic chemistry has great importance in both technical and daily use. Many natural compounds that are vital for plants and animals, such as proteins, fats, carbohydrates, hemoglobin, chlorophyll, enzymes, hormones and vitamins, and materials that have an important place in daily life such as fibers, certain fuels, medicines, rubber and plastics they evaluated.
Structure of the Atom
The atom is the smallest building block that has all the chemical properties of an element . It consists of a nucleus with a positive charge and a number of electrons that rotate around it equal to the charge of the nucleus. Electrons are dispersed around the nucleus, called "head quant layers", scattered across the energy levels. These layers are from inside to outside; They are named with the letters K, L, M, N, O, P and Q. The maximum number of electrons that each layer can receive is clear and twice the square number of the layer. For example, the maximum number of electrons that an nth layer of an atom can take; It can be calculated with the 2n 2 formula. Accordingly, the first layer K can take up to 2 electrons and the second L layer can take 8 electrons.
The main quant layers are divided into orbits, indicated by the letters s, p, d and f, respectively. K layer has only one orbit, indicated by 1s. The L layer is divided into two orbits, expressed as 2s and 2p. The atomic orbit is a region in the space surrounding the nucleus of the atomic nucleus, most likely occupied by an electron. Orbits can have various shapes. For example, the s orbits are spherical, with an atomic nucleus in their centers.
y s orbit
x
z
K layer has only 1s orbit and L layer has 3 orbits other than 2s. The p orbits lie on either side of the nucleus, both lined up around an axis. Their axes are called 2px, 2py and 2pz. Each orbit can take up to two electrons. Electrons in a fully charged orbit must have opposite spins. Below are 2px, 2py and 2pz orbits;
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Chemical Bonding:
The ionic bond introduced by Kossel is formed by electron transfer between atoms and is due to the tendency of atoms to compare their electronic structures to the most stable electron configuration, that is, to the electronic configuration of the nearest inert gas. An example of ionic bonding, characteristic of inorganic compounds, is the formation of lithium chloride (LiCl). Li atom contains 2 electrons in its inner shell and 1 electron in its outer shell. In contrast, in the K layer of the chlorine (Cl) atom2, L There are 8 electrons in the layer and 7 in the outermost layer M. In this case, the Li atom will lose an electron in its outermost orbit, trying to resemble the electron configuration to the electron configuration of the Helium atom, which was in the previous row on the periodic table. The Cl atom will take an outside electron and try to compare the electron configuration to the Argon atom. As a result, these two atoms will become the most stable for them by forming the lithium chloride compound.
The ionic bond is the electrostatic attraction forces between opposite charged ions. According to Coulomb's Law, ions with opposite charges approach each other by applying gravity with certain forces. This approach continues until the repulsion forces of the outer electron clouds of both ions equal each other. Electronegativity values of atoms play an important role in the formation of an ionic bond between the two ions. Accordingly, the compounds formed by the strong electronegative elements in the upper-right side of the periodic table and the electro-positive elements in the lower-left side are characteristic for salts. Electronegativity values of some important elements are given in the following table, which is developed by Pauling and is named after him;
Pauling Scale (electronegativity increases in the direction of the arrow)
  H2.1 | ||||||
LI 1.0 | BA 1.5 | B 2.0 | C 2.5 | N 3.0 | HE IS 3.5 | F 4.0 |
NA 0.9 | Mg 1.2 | Get 1.5 | Si 1.8 | PA 2.1 | S 2.5 | Cl 3.0 |
K 0.8 | CA 1.0 | BR 2.8 | ||||
Rb 0.8 | SR 1.0 | I 2.5 | ||||
In this scale, fluorine, which has the highest electronegativity value, includes elements that can be encountered in an organic structure with its electronegativity value (4.0) and their electronegativity values. These values are around 1.0 in many metals, 3.5 in oxygen, 2.5 in carbon and 2.1 in hydrogen. The electronegativity of these nonmetals varies depending on their location on the periodic table, but always higher than 1.0. As can be understood from the table, electronegativity is a periodic feature of the elements, it increases from the bottom up and from left to right in the periodic table.If the electronegativity difference between the two atoms is greater than 1.7, an ionic bond is formed between these two atoms, and the atom with the higher electronegativity takes the electrons by converting (-) into the charged anion, and the less atom by giving electrons to the (+) charged cation.
In cases where the difference of electronegativity between the two atoms is less than 1.7, instead of electron exchange between them, a joint occurs and a "covalent bond" occurs between the atoms. As a matter of fact, if the electronegativity difference between the atoms entered into the rectification is between 0.5-1.6, the formation of the "polar covalent bond" and between 0.0-0.4, the formation of the "apolar covalent bonds" can be mentioned. As a best example of the formation of covalent bonds, two hydrogen atoms combining to form hydrogen (H 2 ) molecule reactions. Here, since both atoms share an electron they have with the other atom, the electronic configuration of both atoms resembles helium (He) and creates stability in the molecule.
 |
+
H * + * H H ** H
Covalent bonds have very strong bond energies. The reason for this is that the electron pair forming the bond prevents the positively charged nuclei from repelling each other by settling in the region between the two nuclei while attracting them. In this way, the electrons located between the two nuclei connect the nuclei to each other and this binding keeps the distance between the atoms constant within very narrow boundaries. The fixed distance between atoms is called "bond length".
All of the covalent bonds occur by electron sharing. But; The participation share of the electrons participating in this sharing is not always at the same rate. For example, since the electronegativities of both atoms in the bond formed between carbon and sulfur are equal (2.5), the participation rates of electrons in the bond are almost equal and the bond formed is the apolar covalent bond . However, if electronegativities such as hydrogen and chlorine had a bond between two different atoms, the bond to be established would have been called polar covalent bonds, since the rate of electron involvement would change .
Whether polar or apolar, covalent bonds are particularly characteristic of the carbon atom.
Electrons that are located in the outermost orbit of the atom and have bonding properties are called “valence electrons”. Structural formulas where valence electrons are shown with dots are also called “Lewis Structures”. Lewis structures for chloroform (CHCl 3 ), Methanol (CH 3 OH) and Ethylamine (C 2 H 5 NH 2 ) can be illustrated as follows;
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CHCl 3 CH 3 OH H 3 CH 2 NH 2
Chloroform Methanol Ethylamine
In the demonstration of molecular formulas, the electron pair that forms the covalent bond is indicated by a small line (-). Other valence electrons do not have to be displayed. As seen in the formulas above, carbon 4, nitrogen 3, oxygen 2, hydrogen and halogen atoms are also capable of making a covalent bond.
Atomic Orbitals
Although the Lewis structure structure mentioned in the previous subject is sufficient to determine the shape of chemical bonds, it is not sufficient to determine the relationship between the structure of a molecule and its susceptibility to chemical reactions. For this reason, the researcher named E. Schrödinger introduced the theory known as “quantum mechanics” in 1926. This theory is based on the principle that a wave accompanies a moving particle. Accordingly, electrons that orbit an atom move not only as particles, but also with waves accompanying them. This theory can explain the phenomenon of electrons being refracted. The motion of an electron in quantum mechanics can be expressed mathematically, and the equations used for this purpose are called the "wave equation" (Schrödinger Equation). For example, the Schrödinger equation for a system with only one electron;
∂ 2 φ ∂ 2 φ ∂ 2 φ 8π 2 m
+ + + (E - V) = 0
∂ x 2 ∂ y 2 ∂ z 2 h 2
It shaped. Here m is the mass of the electron, E is the total energy, V is the potential energy and h is the planck constant. Ψ refers to the square root of the probability that an electron can be found at a particular location in the x, y, and z coordinate system, in which the atomic nucleus is located. This equation can also be applied to systems containing more than one electron. But; In this case, the equation becomes more complex.
There is no exact solution to the Schrödinger equation. However, approximate solutions can be obtained for certain E values. These solution sets are called "Wave Functions (Ψ)". Although there are no definitive solutions for wave functions, this approach is the most important theory used today in explaining wave mechanics, atomic and molecular structures.
Different orbitals, according to quantum theory, have various sizes and shapes, and they are located in special shapes around the atomic nuclei.
SURFACE ACTIVE SUBSTANCE USE IN LEATHER PRODUCTION
The most basic processes in making raw leather are conservation, wetting-softening, hair removal and liming, bating, degreasing, pickling, tanning, retanning, lubrication, painting and finishing. These procedures are usually carried out in the order specified, but it should be noted that not all procedures are required for every skin type. Although the effects of physicochemical events are seen in all of these processes, the use of surfactants in at least two of them is also considered to be very important for the effectiveness of the processes. In these processes, degreasing and lubrication are the steps. In most of the other processes except for conservation from the leather production steps, the use of surfactants is more or less practical.
Raw hides are brought to the factories mostly canned and with less water than normal water, which is a disadvantage for the hides to be produced. Therefore, the first process applied to the leather brought to the factories in this case is wetting - softening. In this process, it is aimed to remove the preservatives such as salt, to take the water-soluble substances out of the skin and to the soaking water and to clean the skins from organic and inorganic dirt. Accordingly, surfactants are used that aid the wetting, cleaning and penetration of dry skin easily, and provide the solubility of substances that dry in the skin and cause the skin to harden.
Surfactants are used in this process in order to increase the penetration of the chemicals used in hair removal and liming processes after wetting, to perform the process effectively, to help emulsification of excess oil in the skin and to prevent vascularization.
The process step in which surfactants are used the most in leather production is degreasing. This process is very important and must be done for sheep skins, fur skins and reptile skins. It is usually done after hair removal. However; If necessary, it can be done in other processes. The natural oil content of leathers is removed by treating them in water-based baths containing relatively high rates of surfactant. Another method of degreasing is the application of oil solvents to the skin and subsequent washing of the solvent, and the removal of the detergent solution and skin oil by washing them out of the skin.
In both cases, surfactants need to have good emulsifying properties. In addition, it should function well in environments with electrolytes and be effective in a wide pH range. For this purpose, fatty alcohol sulfates, alkyl aryl sulfates and water-soluble polyethylene oxide based nonionic surfactants have been the most used in recent years.
Surfactants
Surfactants are substances that allow all types of surfaces to be broken down, eliminated and modified. In many areas these are referred to as soaps, detergents, forming agents, emulsifiers and solvents. These chemicals are; soap and shower gels, home and industrial cleaners, shampoos, hair styling and creams, toothpastes, cosmetics, processed foods, aerosols, fuel oil and dyes are used for different purposes and improve some properties of these materials.
Surfactants are substances that significantly change the surface or interfacial properties of a liquid in which it is dissolved in very small amounts. This; depends on the structural properties of the surfactant. It is a behavior that arises with the desire to take place in different phases with two different sides of the items that are bilateral and have bidirectional orientation. This behavior occurs when the surfactant molecule shows the tendency to migrate to the interface or surfaces. The activities of these substances on the surfaces are defined by measuring various surface properties . In order to understand the behavior of surfactants, it is necessary to examine the various events occurring at the phase boundary in detail.
The main difference between surfactants and other dissolved substances; characterized in that they form a special type of colloidal solution. Solutions of surfactants show some different physical properties. While dilute solutions behave like normal electrolytes, there is a sudden change in electrical properties and deviations from normal as well as various physical properties such as osmotic pressure, turbidity and surface tension at a certain concentration. Mc. Brain stated that these different behaviors can be explained by the formation of microsurgery or micelles in surfactant molecules and ions.
Surfactants are also known as surfactants. Surfactant or surfactant in its simplest sense; When dissolved in a solution or in an anhydrous environment, it is the substance that affects the surfaces, shrinking the surface and reducing its tension and allowing it to spread easily. The term surfactant is an abbreviated form of the Surface Active Agent expression. They are generally organic compounds. Due to their structure, they show semi-soluble properties in both organic solvent and aqueous solutions. They are also known as amphipathic or amphiphilic compounds, and it should be understood that they do not prefer to stay in any phase and that they show accumulation and activity at the phase interfaces. It is also not possible to state that all amphiphilic molecules will always show such activity. Indeed, only more or less balanced hydrophilic and lipophilic tendencies are observed in the amphiphilic molecules to migrate to the surface and interfaces. If the amphiphilic molecule has more hydrophilic or more hydrophobic properties, the molecule will show a tendency to be in a single phase.
These chemicals help dissolve hydrophobic compounds in aqueous solutions due to their asymmetric structures and chemical groups with different structures and properties. These properties are important in terms of leather production processes and are used in the execution of the processes and in obtaining some leather properties.
Although soaps, which have been known and used for a long time, show such properties, they form a separate group of surfactants since they are obtained from fats and oils, and there are some differences from the ways in which the surfactants are obtained.
Phase and Interface
In physics, the term phase describes a state of a macroscopic physical system that has a relatively uniform chemical structure and physical properties such as density, crystal structure, refractive index. It expresses the differing state of the structure, which constitutes a system that is simply in balance, and that is chemically and physically identical.
The phase is derived from the Greek word phasis , and it means appearance, but the word has many more meanings. The layers of liquids that do not mix physically chemically with each other are defined as phases. These are systems formed by structures that have the same chemical structure and physical condition and are separated by phase boundaries with substances of other properties. It is known that when mixable substances form a single and homogeneous phase when mixed, substances that do not mix are separated by a certain limit and form different phases. The best-known example of this is oil and water.
Surface or interfaces are the point of contact between the two phases formed by two different systems that do not interfere. The transition region between the two phases is a very thin layer or membrane-shaped region and is several angstroms thick. Interfaces; It is important to determine the behavior and physical properties of two different systems, especially colloidal systems.
In colloidal systems, at least one of the components is in sizes ranging from 1 nm to 1 µm . Colloids contain either large molecules or small particles. The term micro heterogeneous systems would be a more accurate definition since colloidal systems dissolve rather than dissolve.
Common basic properties of colloidal systems; The ratio of the surface area to the mass is large for the particles that realize the dispersion. Typical surface phenomena such as adsorption and electrical double layer are observed at the interfaces between the dispersion phase and the phase that is the dispersion medium, and it is possible to determine the physical properties of the entire system by examining them. For example; In emulsions and foams, which are colloidal systems, approaches to the solution of some problems are provided by examining the surfaces rather than the system itself. Since the interfaces in any heterogeneous system reflect the characteristics of the whole system, the interfaces must be examined in order to interpret all the behaviors of the system. For example; emulsification, wetting, spreading, foaming, detergent effect, The adsorption effect and the occurrence of these events by interaction depend on the events that occur at the interfaces between the two phases. It is known that there are five different interfaces. These;
Solid-Gas Surface
Solid-Liquid
Solid-Solid
Liquid-Gas Surface
Liquid-Liquid
Surfactants are effective at the interface between the two separate phases here. There are many such surfaces in the human body. These surfaces are in various structures from the outer skin layer to the cell membrane. These surfaces are strong biological organs and are organs that pass the appropriate components, active carrier, active barrier and control diffusion.
Since solubility is an important criterion when examining surfactants, systems with a liquid phase will be emphasized more. However; Liquid-solid and solid-gas systems are also important to understand the physicochemical events occurring in waterproofing and finishing in leather production.
Properties of Water as a Solvent System
Before talking about the properties of surfactants and other water-soluble substances, some general properties of water must be known. Since it is abundant and inexpensive, water is used practically in realizing many chemical processes, formulating and preparing products. Various important accepted features of water can be listed as follows;
a) Water is a good solvent,
b) It has a very high boiling point ( boils at 100 0 C or 212 0 F at 760 mm Hg pressure )
c) It has a stable structure,
d) It is known as a widely used reaction medium for neutralization and hydrolysis reactions.
These properties of water arise from the solid bonding of the molecule and its structural polarization. This polar structure of water is attributed to an unsymmetrical molecule structure as schematized below. Due to the structural nature of the water, the oxygen part of the molecule is more negative than the hydrogen tip. This polar property makes water a very good solvent for other polar and ionized chemicals.
The water itself shows only a little ionization tendency, or separation into very low counter charged groups in the molecule. Therefore; It is known that water is chemically very stable. However, it hydrolyzes with some chemicals and reacts. Its structure is stable even at very high temperatures. Many reactions can be catalyzed by adding a small amount of water (Example corrosion and rust formation). However; most acids, bases, and salts can easily be ionized in aqueous solutions. Reactions known as neutralization are a reaction of acid and base ions, resulting in a salt and usually water.
While in liquid form, water combined molecules so strongly that a lot of heat energy is needed to release the molecule and turn it into gas. As a result; the boiling point of water and the heat of evaporation are too high for this small molecular weight substance.
Boundary Surface Tension and Surface Tension of Water
An important feature about the attraction of molecules and the combination of molecules related to its internal structure in a liquid is its surface tension. The table below gives the molecular weights, boiling points and surface tensions of commonly used chemicals.
Molecular Weight | Boiling Point (° C @ 760mm. Hg) | Surface Tension (@ 20 ° C Dyn / cm) | |
Water (H 2 O) | 18 | one hundred | 73 |
Methanol (CH 3 OH) | 32 | 65 | 22 |
Ethanol (C 2 H 5 OH) | 46 | 78 | 22 |
Ether (C 2 H 5 OC 2 H 5 ) | 74 | 34 | 17 |
Table: Some physical properties of water and various chemicals.
All liquids have intermolecular attraction forces, the intensity of which varies according to the type of fluid, and these forces are called cohesion forces. A molecule in the center of the water phase or another liquid is attracted very strongly by all of its close neighbors. This attraction is equal in all directions and is spherical and symmetrical. Thus, the forces acting on a molecule in the liquid balance each other. Also; Since the molecules in the liquid are under the influence of more attraction force than those on the surface, their potential energy is lower than the potential energy of the molecules on the surface. Because the greater the gravitational forces acting on an object in general, the lower the potential energy of the object. However, a molecule on the surface does not have any neighboring molecules on the air or gas phase side, or it is not subject to attraction in this direction since the density in the vapor phase is lower than the liquid phase. For this reason, the molecules on the liquid surface are drawn towards the interior in this region. This creates a force that acts on the surface of a drum, such as the skin stretched from one side to the other. This effect is called surface tension and is shown in the figure below. The desire to act towards creating a minimum surface area of the unit volume of water, forming a drop or sphere shape results from this effect. For this reason, the molecules on the liquid surface are drawn towards the interior in this region. This creates a force that acts on the surface of a drum, such as the skin stretched from one side to the other. This effect is called surface tension and is shown in the figure below. The desire to act towards creating a minimum surface area of the unit volume of water, forming a drop or sphere shape results from this effect. For this reason, the molecules on the liquid surface are drawn towards the interior in this region. This creates a force that acts on the surface of a drum, such as the skin stretched from one side to the other. This effect is called surface tension and is shown in the figure below. The desire to act towards creating a minimum surface area of the unit volume of water, forming a drop or sphere shape results from this effect.
Figure: Schematic representation of the surface tension and the behavior of surfactant molecules in solution.
In such a liquid, a work must be done against cohesion forces between the liquid molecules to increase the free surface of the liquid by removing the internal molecules to the surface. As a result, the molar free energy of the surface region of the liquid is higher than the molar free energy of the other part of the liquid.
The surface tension (γ) of a liquid is the force per unit length that opposes the surface expansion of the liquid on the surface. Surface tension acts parallel to the surface. The unit of surface tension in SI system is newton per meter (Nm -1 ) or Jm -2 (since 1J = Nm) . The unit in the CGS system is dyn / cm or erg / cm 2 . For example, water surface tension of 20 0 C was 72.8 dyne / cm or 72.8 erg / cm 2 when the water surface of 20 0 C for 1 cm 2 in order to expand 72.8 erglik an energy or in other words a 1 cm along to cut relationships between molecules on the liquid surface 72.8 A strong force is needed.
Surface tension is a physicochemical dimension of the water molecule having a polar structure. This tension on the surface decreases significantly with the increase in temperature as seen in the figure below. As a result, hot water is a better cleaning agent due to the lower surface tension. The low surface tension gives it a good wetting agent feature based on better penetration between the pores and slits. Because the phenomenon of joining two different units as a bridge to a small port of a substance with high surface tension is eliminated.
Surfactants and Effects on Boundary Surfaces
These chemicals help dissolve hydrophobic compounds in aqueous solutions due to their asymmetric structure and their presence in different chemical groups.
Although they have such characteristics in soaps that have been known and used for a long time, they form a separate group of surfactants since they are obtained from fats and oils and are produced using different production processes from the ways in which the surfactants are mentioned.
In the simplest sense of surfactant; It is a substance known as wetting agent that allows a liquid to spread easily by lowering the surface tension. The term surfactant is an abbreviated form of the Surface Active Agent expression. They are generally organic compounds. Due to their structure, they show semi-soluble properties in both organic and aqueous solutions. They are also known as amphipathic compounds and it should be understood from this definition that they prefer not to stay in any phase and that they accumulate in the phase interfaces.
Figure: Schematic representation of the effects of surfactants in solution.
A surfactant, meaning surfactant, is characterized by the absorption tendency on surfaces or interfaces. Interfacial expression means a border region between any two phases that do not interfere with each other. Surface expression is an expression used when one of the phases is gas. This is generally the case when the gas phase is air.
By absorbing a surfactant at the interface, it is possible to expand this interface by reducing the free energy of that phase boundary. The term interfacial tension is often used to replace the interfacial free energy per unit area. Hence, the surface tension of the water is considered equal to the interfacial free energy per unit area of the boundary between the water and the air above it. When this boundary is covered by surfactant molecules, the surface tension is reduced. In other words, the amount of work required for the expansion of the interface is reduced. Meanwhile, the more intense surfactant agglomeration on the surface, the greater the decrease in surface tension.
Figure: Physicochemical phenomena due to surfactant surface tension in aqueous solution.
Surfactants can be absorbed on the surfaces between the five different phases listed above. Almost all of these are important for leather production and are effective in the execution of processes. However, since many processes are carried out as the delivery of any solution to the skin, the liquid phases will be treated more heavily in this course. In the liquid phase, it is usually water. But; there may be other liquids. The interfaces formed by the liquid as a phase are given in the table below with examples.
Interface | System Type | Product |
Solid-Liquid | Suspension | Paints Carried in Solvent, Pigment Pastes |
Liquid-Liquid | Emulsion | Milk, Cream, Leather Finisher |
Liquid-Gas | Foam | Shaving Cream, Foam Finish |
Table 1: Examples of interfaces formed by the liquid phase
Many formulated products contain several types of interfaces at the same time. Water-based paints and paper coating paints are the best known examples. However; When evaluated colloidally, they are very complex systems containing both solid-liquid (disperse pigment particles) and liquid-liquid (latex or other binder droplets) interfaces. In addition; foam formation is the most common (but undesirable) phenomenon in such systems. All interfaces are balanced by surfactants. The total interface area of such a system is very large. The oil-water and solid-water interfaces of one liter of paint cover several football fields.
As mentioned above; Gathering tendency at the interfaces is considered as one of the basic features of a surfactant. In principle, the stronger this tendency, the better the surfactant properties. The concentration (concentration value) of the surfactant in the boundary region depends on the structure of the surfactant as well as the structure of the two phases that meet at the interface. For this reason, a very important point in the use of surfactant is that there is no universally surfactant substance for all purposes. The choice of surfactant depends on the exercise. A good surfactant should have low solubility within the main phases. Some surfactants (and various surfactants macromolecules) only dissolve at the oil-water interface. Such compounds are difficult to use, but they are very effective in lowering the interfacial tension.
Certainly, there is a limit in the effect of reducing the surface or interfacial tension with the surfactant. Normally, this limit value is reached when micelles begin to form in the main solution. Table 1.2 shows the effectiveness of surfactants effective in reducing surface and interfacial tension. The values given are typical values achieved with normal mild-effect liquid detergents. With special formulations expressed as ultra low interfacial tension, values such as 10 -3 mN / m or less can be achieved, for example.
Interface Types | Interfacial Tension (mN / m) |
Air-Water | 72-73 |
Air- 10% NaOH Aqueous Solution | 78 |
Air-Water Surfactant Solution | 28-30 |
Aliphatic Hydrocarbon-Water | 40-50 |
Aromatic Hydrocarbon-Water | 20-30 |
Hydrocarbon-Aqueous Surfactant Solution | 1-10 |
In systems consisting of two dense phases such as liquid-liquid and liquid-solid, any change that may occur in the composition of one of the phases generally changes the interface energy to a degree that can be measured. The inclusion of a soluble substance in a liquid phase changes the surface energy of the liquid phase. For example; The energy of the water-air surface is 72.75 erg / cm 2 , 73.0 erg / cm 2 of 1 % NaOH solution and 77.5 erg / cm 2 of 10% NaOH solution under standard conditions . concentration The surface tension of the aqueous NaOH solution as a function is given in the graph below. From this chart; It is understood that quite concentrated NaOH concentrations should be reached in order to achieve a significant increase in surface tension. By adding any soluble substance, the change in the surface energy of the solution can be observed as rising or falling.
Figure:
The oldest known surfactants are soaps. An aqueous solution of a soap gives the typical curve of the concentration-surface tension change of surfactants. An example of this is the surface tension graph of diluted sodium oleate solutions (figure).
Figure:
Surface activity has been studied in the most detailed aqueous systems. For this reason, the most widely known surfactants are water-soluble. In contrast, surface activity is also a feature seen in waterless systems and this type of systems are encountered in leather production.
Properties of Surfactants
a) They show a tendency to gather at interfaces.
b) The effect of lowering the interfacial tension is limited by micelle formation when a certain concentration is reached.
c) There is no universal surfactant. The effect of reducing the boundary surface tension depends on the structure of the surfactant and the structure of the two phases.
d) Surfactant molecules have an asymmetrical structure. The molecule consisting of two different parts is also called amphiphil.
e) Chain length, degree of branching, location of the polar group on the chain are the structural features that affect the physicochemical properties of the surfactant.
f) Each surfactant has superior properties compared to others in terms of certain functions. This provides specific use for certain surfactants.
g) The vast majority of surfactants are characterized by a substantially linear molecular part. This linear structure is larger than the width of the molecule. This linear structure has a radical compatible with the solvent system at one end and a radical incompatible with the solvent system at the other end.
h) Although natural surfactants are needed especially for domestic use, today, with a few exceptions, they are produced through organic synthesis, all of which are sourced from petrochemical and oil chemicals.
ı) Whether surfactants have the desired properties can generally be estimated by looking at their chemical structure. The location of the hydrophilic group in the organic molecule also affects the functional properties of the surfactant.
In order for a substance to be considered as a surfactant, it must have the following properties.
1. Solubility: The surfactants which generally dissolve show the highest surface activity. Surfactants should be dissolved at least in one phase of the system. Although Bentonite soil has surface active properties, it has no solubility feature. Therefore, it is not a surfactant.
2. Amphipathic Structure: Surfactant molecules carry groups with opposite tendency to dissolve.
3. Orientation at the Interface: Surfactant molecules or ions form layers directed at the interface phase.
4. Adsorption at the Interface: The equilibrium concentration of a surfactant at the interface is greater than the concentration in the mother liquor. Therefore, in increasing concentrations, they decrease the surface tension more than expected.
5. Micelle Formulated: When the concentration of surfactants in the mother solution exceeds a certain limit value, they form molecules or ion clusters named as micelle.
6. Functional Features: Surfactant solutions should show some of the functional features such as cleaning, foaming, wetting, emulsifying, dissolving and dispersing.
Use of Surfactants
While surfactants are used in our daily lives to facilitate and activate any of our activities, they have found widespread use in industrial applications in carrying out many processes. The compositions of the most commonly used household cleaning and personal care products consist of surfactants or a mixture thereof. Participating in the composition of laundry, dishes and substances used in cleaning the area, toothpaste, hair shampoos and creams, and even various aerosols and deodorants are examples that demonstrate that they have entered human life very widely.
Surfactants are used in the textile industry in washing, whitening and dyeing processes, in the production of easily wettable fabrics and cloths designed for use in different areas, and in the production of waterproof and wet-resistant fabrics. It is used to provide opacity in the cosmetic industry of the surfactants, to adjust the viscosity of various cosmetic substances, to increase their effectiveness and to provide easier and homogeneous application of the cosmetic substance by cleaning the surface. It is used in the chemical industry for obtaining polymeric compounds, especially as emulsifier, in the production of paints, waxes and brighteners, in pigment production, in the preparation of various chemical and auxiliary formulations and their application in a specific field. In the production of agricultural chemicals; Various fertilizers and plant growth regulators are used in formulating herbicides, insecticides and fungicides. It is widely used in the food industry for staining and delaying deterioration, for controlling consistency in baked products, as emulsifier for chocolate and various fatty products, to prevent sudden evaporation of water in frying oils.
Surfactants are used in the leather industry for wetting dried and kept raw leather, cleaning wool and bristle fibers from oil, greasy and foreign materials, protecting leather from microorganism activities, emulsifying the natural oil of the raw leather, removing dye in the dyeing, adjusting the leather and moistening of the leather. It is used in impermeability, in finishing paint formulations, as well as in penetrator formulations to adjust the density.
Structural Properties of Surfactants
A surfactant is, for example, an organic compound containing two water-soluble and water-insoluble properties and two distinct structural groups in the same molecule. The physical properties of the molecule emerge from this difference in its structure and is named depending on this characteristic feature. Whether surfactants have the desired properties can usually be estimated by looking at their chemical structure.
Amphiphil expression is sometimes used synonymously with surfactant. This word is derived from the Greek term amphi and means both. The expression relates to the surfactant molecule consisting of at least two parts. The term amphipathic refers to the opposition that occurs due to different structures in the same molecule or ion. One of these parts is dissolved in a specific fluid (lyophilic part) while the other part is not dissolved in this substance (lyophobic part). If this fluid is water, the hydrophilic and hydrophobic portion is mentioned, respectively. The hydrophilic part is described as the head group and the hydrophobic part is described as the tail part. The figure shows the hydrophilic and hydrophobic portions of a surfactant molecule.
Hydrophilic Head Group Hydrophobic Tail
Figure 1.1. Schematic Representation of a Surfactant Molecule
Figure: Structural structure and orientation of a surfactant molecule.
The hydrophobic portion of the surfactant can be in the form of linear or branched alkyl groups. The polar headband is usually (but not always so) connected to one end of the alkyl chain. The length of the chain has 8 to 18 C atoms. The length of the chain, the degree of branching and the location of the polar group on the chain are important parameters for the physicochemical properties of a surfactant.
The polar portion of the surfactant molecule can be ionic or non-ionic, and the choice of the polar group largely determines the properties of the surfactant. For non-ionic surfactants, the size of the polar head assembly can be changed as desired. In ionic surfactants, this probability is somewhat constant.
The image of the micelles formed by the surfactant molecules in the solution, which will be explained in the next section, resembles a cluster. The hydrophobic group of the surfactant is directed towards the interior of the cluster, and the polar head group is oriented in the direction of the solvent. Therefore, a micelle is a polar aggregate with a high degree of water solubility that does not have much surface activity.
There are also compounds that are collected at the interfaces and do not form micelles easily and also have weak surface activity. These compounds are described as hydrotropic agents and are used as adjuvants in many surfactant formulations. These are used for the purpose of breaking down the packages formed by surfactants with low surface activity regularly. Thus, the addition of a hydrotropic substance is a way of preventing the formation of high viscosity liquid crystal phases, which represent a problem most known in surfactant formulations.
Aggregate Formation in Solution
As already mentioned, a characteristic feature of surfactants is the tendency to absorb at the interfaces. Another main feature of surfactants is that the unimer in the solution tends to form aggregates, also called micelles. Free or unbound surfactant molecules are described unitary in the literature. Micelle formation or micelleization; It appears as an alternative mechanism for absorption at the interfaces to cut the hydrophobic groups into contact with water and thus reduce the free energy of the system. This is an important phenomenon since when surfactant molecules exist as micelles, they behave very differently than they do as free units in solution. In this case, only surfactant units are effective in reducing the surface or interfacial tension, and dynamic events such as wetting and foaming are guided by collecting the free units in the solution in this region. Micelles can be viewed as a repository for surfactant units.
Micelles appear even in water at very low concentrations of surfactants. The concentration at which micelles begin to form; It is called the critical micelle concentration and is denoted by the term CMC. The critical micelle concentration is an important characteristic for a surfactant.
CHARACTERISTICS OF SURFACTANTS AND THEIR CHARACTERISTICS IN CLASSIFICATION
The most important and basic classification of surfactants is made based on the load of the polar head group. According to this; It is the most common thought and practice to classify surfactants as anionic, cationic, nonionic and zwitterionic. Surfactants belonging to the last class normally contain both an anionic and a cationic charge. In the literature, these are referred to as amphoteric surfactants. However, the use of the term amphoteric in naming is not always the right approach. It should be used synonymously with the term zwitterionic. An amphoteric surfactant is a surfactant that can be cationic, zwitterionic or anionic, depending on pH. Among normal organic substances, simple amino acids are well-known examples of amphoteric compounds. Most of the surfactants mentioned zwitterionically belong to this category. However; other zwitterionic surfactants show a single charge character in all pH regions. As a cationic group, compounds with qaurterner ammonium are examples. Therefore, a surfactant containing a carboxylate group and a quarterner ammonium group is not a rare combination as we can see later, and they are found zwitterionically unless the pH is too low. But it is not an amphoteric surfactant. A surfactant containing a carboxylate group and a quarterner ammonium group is not a rare combination, as we can see later, and they are found zwitterionically unless the pH is too low. But it is not an amphoteric surfactant. A surfactant containing a carboxylate group and a quarterner ammonium group is not a rare combination, as we can see later, and they are found zwitterionically unless the pH is too low. But it is not an amphoteric surfactant.
Many ionic surfactants are monovalent. However, there are also important divalent anionic amphiphil samples. The selection of the counter ion for ionic surfactants has an important role in physicochemical properties. Many anionic surfactants contain sodium as a counter ion. However, other cations such as lithium, potassium, calcium and proton-bearing amines are used as counterions of the surfactant for special purposes. The counter ion of cationic surfactants is usually a halide or methyl sulfate.
In surfactant molecules, the hydrophobic group is normally hydrocarbon (alkyl or alkylaryl) or halogen-containing hydrocarbons. In addition, polydimethylsiloxane or fluorocarbons can also be included in the surfactant molecule for this purpose. Therefore, when a classification is made depending on its chemical structure, silicon and fluorocarbon hydrophobic chain surfactants should be counted as the fifth group in addition to the other four groups. These last group of surfactants are especially effective in anhydrous systems. Those carrying olefinic groups are less hydrophobic than those carrying saturated hydrocarbons. Silicon-containing hydrophobic products are being used more commercially today. Surfactants belonging to this last group are also widely used in leather production processes.
The location of the hydrophilic group in the organic molecule is effective on the functional properties of the surfactant. For example; If the hydrophilic group is in the middle of the hydrophobic chain or if the hydrophobic group contains two or more chains, that surfactant shows strong wetting property when it is located in the middle of the branching. It is known that the cleaning effect is more pronounced when the hydrophilic group of the surfactant is located at the end of the hydrophobic chain.
CH 3 (CH 2 ) 3 CH- (CH 2 ) 6 -CH 3 │ O- SO 3 Na Sodium-1- (n-butyl octyl sulfate) Strong Wetting Agent | CH 3 (CH 2 ) 10 CH 2 -O-SO 3 Na Sodium-n-dodecyl sulfate Strong Cleaning |
Different ways to prepare primary alcohols from the raw materials used in the synthesis of surfactants are given in the table below. This chart shows the flow chart of Zeigler-Natta ethylene polymerization, reduction of fatty acid methyl esters, hydroformulation of high olefins (oxo process) from left to right.
Chart …. Zeigler-Natta Ethylene Polymerization, Reduction of Fatty Acid Methyl Esters, Hydroformulation of High Olefins (Oxo Process) Flow Chart of Processes.
Ethylene Al (C 2 H 5 ) 3 Higher Molecule Aluminum Alkyls
Linear Alcohols Wide Molecular Weight Distribution
fractionation Linear Surface Active | triglycerides
CH 3 OH Fatty Acid Methyl Esters
Fatty Acid Methyl Ester Fragmentation
H 2 catalyst alcohols Item Field | Kerosene (Kerosene)
fractionation n-Alkan Fragment
dehydrogenation n-Olefins  CO + H 2 catalyst Branched and Linear Alcohols Surfactant Area |
There are some uncertainties in the classification of several surfactants. For example; Aminoxide surfactants are sometimes mentioned zwitterionically, sometimes cationically, and sometimes nonionically. Their charge is pH dependent. It can be seen that it has either neutral anionic and cationic charges in neutral state or it is dipolar nonionic compounds. Again; Fatty amine ethoxylates contain both an amino nitrogen atom as a cationic polar group and a polyoxy ethylene chain as a nonionic polar group. Therefore, they can be evaluated within either cationics or nonionics class. If the polyoxyethylene chain is too long in the molecule, the nonionic character is dominant. However; In medium and short chains, physicochemical properties are basically similar to those of cationic surfactants. Both sulfate, Surfactants containing an anionic group such as phosphate or carboxylate, as well as a polyoxyethylene chain are also commonly found. These surfactants (known as ether sulfates, for example) typically contain short polyoxyethylene chains consisting of 2-3 oxyethylene units and are always characterized as anionics because of their dissolution properties.
The classification of surfactants is generally done depending on their area of use and considering their chemical structure. Accordingly, a general classification is given in Table below.
Schedule … .. Classification of Surface Active Substances According to Their Chemical Structure.
1. Anionic Surfactants
1.1. Carboxylic Acids and Salts
1.2. Sulfonic Acids and Salts
1.3. Sulfuric Acid Esters and Salts
1.4. Phosphate Esters and Salts
2. Nonionic Surfactants
2.1. Polyoxy Ethylene Derivatives
2.1.1. Ethoxylated Alkylphenols
2.1.2. Ethoxylated Aliphatic Alcohols
2.1.3. Ethoxylated Glycerin Esters
2.1.4. Ethoxylated Polyol Esters
2.1.5. Ethoxylated Fatty Acids
2.2. Fatty Acid Amides
2.3. Alkylene Oxide Block Copolymers
3. Cationic Surfactants
3.1. Aliphatic Mono-, Di- and Polyamines
3.2. Amine Oxides and Substituted Amines
3.3. Quaternary Ammonium Salts
4. Zwitterionic (Amphoteric) Surfactants
4.1. Chemical Structures Carrying Amino and Carboxyl Groups Together
4.2. Chemical Structures Carrying Amino and Sulfuric Ester Groups
4.3. Chemical Structures Carrying Amino and Alkan Sulfonic Acid Groups Together
4.4. Chemical Structures Carrying Amino and Aromatic Sulfonic Acid Groups Together
5. Various Chemical Composition Surfactants
5.1. Silicone-Oxyethylene Copolymer
5.2. fluorocarbons
5.2.1. Anionic Finish Group Fluorocarbon Skeleton
5.2.2. Cationic Finish Group Fluorocarbon Skeleton
ANIONIC SURFACE ACTIVE SUBSTANCES
Today, the most used surfactant class is anionic surfactants and these constitute 70-75% of the total consumption. The hydrophilic particle in anionic surfactants is a negatively charged polar group. This polar group is the carboxylate, sulfonate, sulfate or phosphate group. Therefore; subgroups of this surfactant class; alkali carboxylates, or soaps, sulfates, sulfonates and phosphates with less usage rates. This is due to the many types of hydrophobic groups that can be modified by the addition of special anionic chemical structures on the basis of such a large class of surfactants. The importance of anionic surfactants depends more on their economical nature.
The solubility of sodium salts of all four subgroups of anionic surfactants in soft water and dilute alkaline solution is approximately the same. In neutral or acidic environments and environments with heavy metal ions, the dissolution power of carboxylate is less than that of other groups. Sodium and potassium salts are generally more soluble in water and less in hydrocarbons. Calcium, barium and magnesium salts have more dissolution power in hydrocarbons and less in water. Ammonium and amine salts such as triethanol are appropriately assisted with water and hydrocarbons. Therefore, they are widely used in emulsification and detergent applications. The best known examples of anionic surfactants are soaps, fatty acid salts, which have been used in cleaning activities since ancient times.
Fatty Acid Salts (Carboxylates)
The two commercially important subgroups of this group are soaps and aminocarboxylates . Rub the soap's most important representatives and a long-term effect utilized for the relief of human needs; It is derived from natural animal and vegetable oils in solid and liquid form. Although acids with chain lengths generally greater than 10 carbons have beneficial properties in terms of surface activity, it is possible to use acids with up to 8 carbon atoms for some purposes. Therefore; Soaps, C 9 - C 12 R-alkyl group and M is a metallic ion or amine ion, (RCOO - ) (M +) in the composition. Short chain sodium and potassium salts have higher water solubility when used in sufficient concentrations to achieve desired surface properties. Solubility is limited in water-based uses when the chain length exceeds approximately 20 carbons. Higher molecular weight acids; It has sufficient solubility in anhydrous systems such as oils, dry cleaning solvents and other such systems.
The biggest advantage of fatty acid soaps is that they can be obtained from natural and renewable sources. In almost all carboxylic acids, the acid is neutralized with sodium and potassium. However; Amine salts are also common for some specific uses. The main disadvantages of carboxylic acid soaps are; di- and trivalent cations ( heavy metals such as Mg +2 , Ca +2 , Ba +2 , Fe +3 and Al +3 ) They are sensitive to the environments they are in, the environments where there is a high concentration of salt such as NaCl, even if they are monovalent, and the baths with low pH, which causes the formation of free fatty acids that are insoluble in water. Organic ester-forming reagents such as ethylenediamine tetraacetic acid (EDTA) and nitriloacetic acid (sequester), which are used to prevent collapse disadvantages in the environments where cations are present, prevent the binding of heavy metal ions in the non-ionic complex, thereby forming soap cuts. However, the cost of the water softened with the reagent that performs the sequester event increases very much.
(HCOOCCH 2 ) 2 NCH 2 CH 2 (CH 2 COOH) 2 N (CH 2 COOH) 3
EDTA Nitriloacetic acid
Figure: Chemical Auxiliary Agents That Can Form Organic Esters.
Soap production is cheap. Also; Unlike home-made alkyl benzene sulphonates, they can be degraded in wastewater treatment. Another preferred reason for soaps is that polyphosphates used in detergent formulations cause excessive growth of algae in lakes and rivers.
Another group of carboxylic acid derivatives is anionic surfactant group aminocarboxylates. Today, known as N-Acylsarcosinates and acylated protein hydrolasates, they are both aminocarboxylates, which are used in personal care products and are not harmful to health. They can be used more smoothly in hard waters than soaps. Thanks to the hydrophilic tendency of the amide bonds in its molecules and the solubility of the molecule, the activity of carboxylate ions in the surfactant does not occur with the presence of Ca + 2 and Mg + 2 ions in hard water .
Sodium-N-lauryl sarcosinate (N-acyl sarcosinate) obtained from coconut fatty acids has good foaming properties. These surfactants are; Since it is not harmful to health, it is used in formulating personal skin cleaning and care products, oral cleaning products, toothpastes and surgical cleaning products. It is widely used in toothpaste, tooth powder and oral cleaning waters as it prevents the activity of enzymes that convert glucose into lactic acid in the mouth. N-acyl sarcosinates are obtained synthetically from the condensation of a fatty acid chloride in aqueous alkaline solution, such as N-methyl glycine, derived from methylamine, formaldehyde and sodium cyanide, and a fatty acid chloride.
CH 3 CH 3
│ │
RCOCl + NHCH 2 COONa + NaOH RCONCH 2 COONa + NaCl + H 2 O Figure: Conversion of N-methyl Glyin to N-acyl Sarcosinates with Fatty Acid Chlorides.
Acylated protein hydrolysates are another group of carboxylic acid surfactants. These; They are obtained by direct condensation of fatty acids with protein hydrolysates or by acylation of fatty acid chlorides with fatty acid amino carboxylates. They are less effective as surfactants.
sulfonates
Surfactants based on sulfonic acid salts are similar to sulfate ester-based surfactants in chemical structure. Besides; There are important differences in chemical stability and properties. As with sulfates, the presence of a wide variety of hydrophobic groups in the surfactants belonging to this group causes differences in their area of use and properties.
Some sulfonic acid based surfactants XIX. Although it is known that it was produced according to the sulfate oils method by the sulfuric acid process at the end of the century, the first commercially available products started to be produced as a result of the shortage of raw materials in Germany during the First World War. In these years, short chain sodium alkyl naphthalene sulfonates have been developed as chemicals with good wetting properties, although they have weak detergent properties. This chemical is still used today and it is used in some agricultural and photography applications as emulsifying agents and dispersing agents. In the years following the war, the consumption of these substances in the chemical industries of the UK, Germany and the USA caused the development of new synthetic sulfonate surfactants.
Aliphatic paraffin sulfonates produced by photochemical sulfonation of refinery hydrocarbons in the chemicals that make up the sulfonate group, olefin sulfonates, N-acyl-N-alkyltaurines, Sulfosuccinate esters and their chemical structures, alkylaryl sulfonates and their product. lignin sulfonates can be counted.
The group R has the general formula RSO 3 Na , which is biodegradable or non-degradable hydrocarbon . The surface activity of SO 3 - group is not affected by pH changes or heavy metal ions. Carbon-sulfur bond is not sensitive to oxidation and hydrolysis under normal usage conditions. It is the most produced and most researched group because it is economical. Sulfonates are usually produced as free acids and are then neutralized with alkali metal salts, alkaline earth metal salts or amine salts. As mentioned briefly above, the sulfonates produced can be collected in 7 groups;
a. Alkyl benzene sulfonates
b. Petroleum sulfonates
c. Dialkyl sulfosuccinates
D. Naphthalene sulfonates
to. N-acyl-N-alkyl taurates
f. Fatty acid sul- sulfoesters
Alkyl Benzene Sulfonate
When their powers are compared to aliphatic sulfonates, it is seen that the effect of the benzene ring is equivalent to 3 carbon atoms in the aliphatic chain. Alkyl benzene sulfonic acids are strong acids and are produced as neutral alkali metal salts with very good solubility in all pH ranges. These acids do not precipitate with normal city water. Soil alkali metal salts are less soluble in water than alkali metal and amine salts. Calcium salts are well soluble in hydrocarbons. Alkyl benzene sulfonates are among the most chemically stable surfactants. The sulfonic acid group is not sensitive to acid or hydrolysis under normal storage or use conditions. The compounds are also stable in products formulated to contain oxidizing reagents and against oxidizing reagents in aqueous solutions at concentrations of use.1960 The dodecylbenzene sulfonate (DDBS) with branched chain hydrophobic group up to the years was the most produced and used alkyl benzene sulfonate due to its low price. LAB was started to be produced instead of DDB because the aliphatic group in the benzene ring did not undergo biodegradation of the highly branched propylene tetramer structure and left a permanent residue, and the linear alkyl group in the linear alkyl benzene sulfonates (LABS) was much easier to degrade than the branched chain.
CH 2 ─CH 3
│ CH 3 ─ (CH 2 ) 7 ─CH 2 ─CH ─ ─SO 3 Na LABS
CH 3 CH 3
│ │ CH 3 ─CH─ (CH 2 ─CH─) 2 CH 2 ─CH─ ─SO 3 Na DDBS
Figure: Structural Formulas of LABS and DDBS.
Linear alkyl benzol sulfonate solutions are preferred for their low cost, light color and easy degradation. Its foaming feature is less than DDBSs. However, with strong foam controlling agents such as alkanolamine or alkylamine oxides, they can be regulated for foaming and are used in detergents that have wetting, foaming, emulsifying and dispersing properties that determine the detergent property and are formulated to remove all heavy dirt.
The difference in the production of LABS and DDBS is in the steps until the production of alkyl benzene. The subsequent sulforation and neutralization processes are carried out with almost the same setup and balances.
- Alkylation of Benzene
or
- -sulfonation
the 3.Nötralizasyo
Figure: Akil Benzene Handling, Phoning and Neutralization Procedures.
Production of DDB starts with the process of obtaining propylene tetramer (dodecene). Propylene tetramer and benzene are then converted into DDB by the Friedel-Crafts reaction using AlCl 3 or HF catalyst. The most convenient way to obtain propylene tetramer is simple catalyst polymerization.
Figure: Simple Catalytic Polymerization in Obtaining Propylene Tetramers.
Here; Solid phosphoric acid is used as the catalyst. Reaction energy is very low. In addition, the molecular weight of the polymer can be adjusted by reactivating the temperature and the light product.
LAB production can be done by 3 methods. These:
a. Obtaining linear olefin by dehydrogenation from linear paraffin and putting it into Friedel-Crafts reaction with benzene.
b. Monochlorization, dehydrohalogenation of linear paraffins and reacting the olefin thus formed with benzene using an acid catalyst.
c. Monochlorization of linear paraffins and reaction of this monochlore paraffin and benzene with AlCl 3 .
Figure: Monochlorization of linear paraffins and reaction of this monochloride paraffin and benzene with the help of AlCl 3 .
Straight chain olefin or paraffins are obtained by the following methods:
- Polymerization of ethylene to α-olefins by Ziegler or other polymerization methods. With this process, products of high purity but not cheap are addressed.
- Obtaining long straight chain paraffins from gas oil (carosene) by molecular sieve or extraction.
- Cracking of wax and similar inexpensive paraffins (α-olefins),
- Obtaining fatty alcohols by hydrogenation from methyl esters of natural fatty acids.
Dialkyl sulfosuccinates
Dialkylsulfosuccinates, a highly effective anionic surfactant group in systems containing low inorganic salt, are wetting, wetting, protecting and dissolving, and are obtained by the esterification of maleic anhydride by coupling bisulfite to the double bond.
ROOCCH ROOCCHSO 3 Na
║ + NaHSO 3 ROOCCH ROOCCH 2
Figure: Obtaining Dialkyl Sulfosuccinate From Maleic Anhydride Ester.
Naphthalene sulfonates
Naphthalene sulfonates are both very easy and highly soluble in water. Although strong surface is actively effective in soft waters, they are ineffective in hard waters. They are resistant to hydrolysis in alkaline and acidic environments. This surfactant group is effective in dissolving and suspending in wetting and dispersing systems.
Shape: Alkyl Naphthalene Sulphonate
N-acyl-N-alkyl taurates
The fact that raw material prices were quite high caused N-acyl-N-alkyl taurates to be preferred for special purposes.Figure: Structure of N-acyl-N-alkyl Taurate.
The group H 2 NCH 2 SO 3 Na is called taurine. Taurates have some usage advantages. These;
a) They are stable against hydrolysis in acidic and alkaline environments in their use concentrations.
b) There is no performance loss when used in hard waters.
c) They can be biodegradable.
d) Depending on the molecular structure, they have either strong wetting or strong cleaning properties. For example, when R = C 11-17 and R ' = CH 3 or C 2 H 5, it gains strong wetting , and when R and R ' = C 6-9, it gets strong wetting.
Fatty Acid β-Sulfo Esters
This surfactant group has good wetting properties as well as low foaming properties. Although they are produced for domestic use only, the production values are not suitable.
RCOCl +
HOCH 2 CH 2 SO 3 Na RCOOCH 2 CH 2 SO 3 Na + HCl
HOCH 2 CH 2 SO 3 Na RCOOCH 2 CH 2 SO 3 Na + HClOlefin Sulfonates
Olefin Sulfonates can be represented by the general formula R ' CH = CH (CH 2 ) x SO 3 Na, and linear 14 -olefins from C 14-18 are produced for research and commercial purposes. Its biodegradability is better than linear alkyl benzenes and it has advantages in use because of its toxicity and less skin burning. However, the high cost of their production prevents them from being used widely and limits them.
Olefin sulfonates are obtained in two ways. The first way; It covers cracking of paraffin waxes, as in the production of linear alkyl benzene, and cheap olefins containing diene and naphthenic impurities are obtained. The second way; It is based on the telomerization of ethylene with triethyl aluminum or similar catalysts. Compared to the first way, it is a technique that can produce more expensive but good quality olefins. A wide range of olefins is obtained on both paths. Apart from the effective activity range of C 10-18 , olefins are also obtained with chain lengths greater than C 18 and less than C 10 .
Sulfonation of olefins is done with SO 3 . The reaction is very complex. While alken sulfone, acid and sulton are formed as the main product, sulfone sulfonic acid, alkene disulfonates and other products are formed as by-products.
R-CH 2 -CH-CH 2 SO 3 Na R-CH-CH 2 -CH 2 SO 3 Na
│ │
OH OH
Sodium-2-hydroxy alkane sulfonate Sodium-3-hydroxy alkane sulfonate
Figure: Sodium-2-hydroxy Alkan Sulphonate and Sodium-3-hydroxy Alkan Sulphonate
sulfates
Although they have a very close chemical structure, sulfonic acid salts and sulfuric acid esters differ in their chemical properties, hydrolytic stability and surfactant properties. Some of these differences; It is thought to be related to the binding of the sulfate group with the hydrophobic moiety in a different way than in the sulfonates. While this binding in sulfates is in the form of carbon-oxygen-sulfur, it is in the form of carbon-sulfur in sulfonates. Such apparently small differences in chemical structure can lead to differences in polarization of the head group, different degree of ion binding in solution and different hydration value. All of these can change the surfactant properties of that substance.
As the name suggests, sulfate ester surfactants contain a sulfuric acid ester group. This group provides the solubility of the hydrophobic group. They are usually found as alkali and ammonium salts. They are expressed in ROSO 3 - M + generic formulas. R is one of the hydrophobic groups mentioned earlier. While the most well-known examples of this group are simple straight chain aliphatics such as sodium dodecylsulfate, there are also more complex examples and they are used in various processes.
The hydrophilic group in sulfates is -OSO 3 . Unlike sulfonates, the carbon of the hydrophobic group depends on the oxygen atom. The COS bond formed in sulfates is more easily hydrolyzed than the CS bond of sulfonates. Sulfates are more easily hydrolyzed in an acidic environment, these properties limit their use. Ethoxylation and sulfation can be formed on the same hydrophobe to provide the desired dissolution. This type of bonding is done in materials obtained from very cheap raw materials such as tallow alcohols but which do not have sufficient solubility when sulfated.
The synthesis of sulfate esters generally involves either esterification of an alcohol with sulfuric acid, sulfur trioxide or chlorine sulfonic acid or the addition of internal sulfuric acid to a double bond. These reactions are given below.
ROH + H 2 SO 4 (or ClSO 3 H) ROSO 3 H + H 2 O
RCH = CH 2 + H 2 SO 4 RCH (OSO 3 H) CH 3 Although the reactions seem quite simple here, it should not be forgotten that the substrates in the processes are mostly in the form of a mixture of isomers and therefore the finished product is much more complex than it seems.
Surfactant properties of many sulfate products; it can be very sensitive to the composition of the starting material and reaction conditions. While the general physical properties of such substances can be characterized, a precise physicochemical interpretation of experimental measurements such as aggregation and adsorption is not possible.
Sulfate ester surfactants have gained great technical importance as a result of some factors. As the reason for the widespread use of these; In addition to a sufficient chemical stability, they show good water solubility and surface activity, can be produced with very simple synthetic ways and low cost, and can be produced from starting materials obtained from natural and petroleum-based sources that are widely available.
Sulfates are divided into four subgroups:
a) Sulfated alcohols
b) Sulphated natural oils
c) Sulfated acid amide and esters
d) Sulfated alkyl (polyoxyethylene) -phenol and alcohols
Fat Alcohol Sulfates (Alkyl Sulfates)
They are the first synthetic surfactants used in cleaning products. The hydrophobic group is obtained by reduction of fatty acids or esters. II. Before World War, fatty alcohols were prepared by catalytic hydrogenation of natural fatty acids from vegetable and animal by-products. Alcohol was then sulfated by reaction with chlorine sulfonic acid and then neutralized with alkali. The first commercial alcohol sulfate surfactants were introduced to the market in Germany in the first half of the past century and gained great popularity. More recently, alcohols have been produced by various catalytic reactions using ethylene as the starting material. For example, the Ziegler process gives even numbered alcohols equivalent to those obtained from natural fatty acids. A desired chain length product can be obtained and alcohols can be mixed in almost any ratio. As an example, myristic alcohol (C14 ) Although there is not much in natural resources, it can be produced in unlimited amounts with this process.
Alcohols produced in the way known as the “Oxo” process are slightly branched and contain some secondary alcohols. When working with secondary alcohols, sulfation cannot be performed as easily as primary isomers. Also; Since these contain alcohols with both even and odd carbon chains, the physical properties of the manufactured surfactant differ from those obtained from Ziegler process alcohols and natural sources. In addition to these various sources of alcohol, the quality of the product can be improved by using SO 3 in gas phase as a sulfating agent instead of very coarse chlorine sulfonic acid and sulfuric acid . As a result, the surfactants are lighter in color and contain less sodium sulfate as impurities.
Figure: Alkene disulfonic acids and Sulton sulfonic acids
Natural oils are reduced either directly or after transesterification with short chain alcohols before reduction. This system is still used, but there are cheaper methods of obtaining long chain primary alcohol. In one of them, similar to the production of α-olefin, ethylene is firstly telomerized with triethyl aluminum. The aluminum alkyls formed are oxidized with air to form alkoxide. Hydrolysis of alkoxides gives alcohols. This process creates products with good quality but different chain lengths. Also, aluminum compounds are not reused, as in the α-olefin process. In the other method, olefins are hydroformulated with cobalt catalyst, CO and H 2 . The first products formed are aldehydes.
Secondary alkyl sulfates are produced by adding 90-95% H 2 SO 4 to long chain olefins . The resulting products are shown schematically below. Dialkyl sulfate, represented by (2) as a by-product, is undesirable. The formation of this product can only be partially prevented by using excess sulfuric acid. Two approaches have been developed for this. In the first, by adding a solvent to the medium, the semi-ester indicated by (3) is crystallized and the reaction of a second olefin is prevented. Another approach is to add excess NaOH to the sulfatation product. Then the alkaline solution is heated. Thus, dialkyl sulfate is hydrolyzed to give monosulfate.
Figure: Reaction of Long Chain Olefins and Secondary Alkyl Sulfates.
Sulfates consisting of normal primary alcohols have properties similar to the softening characteristics and performance of molecular weight soaps suitable for them. Branched chain alkyl sulphates are strong wetting agents. As the length of the carbon chain increases, the temperature must be increased to reach maximum cleaning and wetting.
Alkyl sulfates are highly stable in hard water and have strong foaming properties. For example, magnesium lauryl sulfate gives a lot of foam with little water. Apart from giving strong foam, alkyl sulfate products also have effective emulsifying and dispersing properties and strong wetting properties. There are also those used as wetting and cleaning reagents in textile processes.
CH 3 (CH 2 ) 10 CH 2 OSO 3 - M +
Lauryl Sulfate
Sulfate Fats and Oils
Sulfate ester fats and oils; It is obtained by reacting many hydroxylated or unsaturated fats and oils with sulfuric acid or chlorine sulfonic acid. These substances represent the oldest commercial synthetic surfactant class, and their use is based on dates when surfactants known as Turkish Red Oil were used. Sulfate fats and oils are heterogeneous substances depending on the structure of the starting materials and production processes. They not only contain sulfate glycerides but also contain sulfate carboxylic acids and hydroxy carboxylic acids formed by the hydrolysis of the starting materials.
Emulsifiers are used as wetting reagents, detergents, preservatives, dispersing agents, textile softeners and lubricants. Derivatives used as lubricants and softeners have efficiency depending on the degree of sulfation.
In the production of sulfated natural oils, tallow, castor oil, cod fish and beef trotter oil are widely used. In addition, peanut oil, soybean oil and oil extracted from the wholemeal portion of rice are used, albeit in a smaller amount. The products are neutralized as sodium salt in the form of semi-sulfated esters.
Fatty Acid Condensation Products
In addition to the aforementioned simple alkyl sulfate ester, more complex sulfate esters of condensing products form an important group of surfactants. This group of surfactants; Bonded groups such as amides, ethers (and polyethers), esters and amines. The general structure of the condensation products containing sulfate groups are given below.
RCO – X - R'OSO 3 - M +
Figure: Structural Formula of Sulfated Fatty Acid Condensation Products.
Here X consists of oxygen (ester), NH, N (amide) groups bonded with alkyl groups. R 'is alkyl, alkylene, hydroxy alkyl or alkoxy alkyl groups. These products have been found to have good wetting and emulsifying properties. These products are included in the content of personal care products and are used in formulating various cosmetic products due to their low skin irritation properties.
The most important examples of this sulfate surfactant class are sulfate monoglycerides and other polyols and sulfate alkanolamides. Sulfate monoglycerides are usually obtained by controlled hydrolysis-sulfatation of triglycerides with the help of sulfuric acid or oleum. Process and final product properties are sensitive to conditions such as temperature, reaction time and concentration of reactants. The natural extraction of starting materials for such processes has created a very important commercial potential in the developing countries of Latin America, Asia and Africa, where triglycerides from animal and vegetable sources are more easily supplied than expensive petroleum raw materials.
Other sulfate polyol esters have also been proposed as surfactants and many patents have been obtained. Sulfated ethylene glycol and pentaerythritol monoesters are important compounds in this regard. However, these were not widely accepted commercially, probably due to the lack of hydrolytic stability of the ether bond.
The disadvantage of alkanol esters mentioned in this group of surfactants can be overcome by using the alkanol amide bond. They are produced by the reaction of hydroxyalkylamides and hydroxyalkylamines with fatty acids or esters and by reaction of epoxides with fatty amides. The second process is not so much preferred as it can cause the formation of many products. These products generally have better hydrolytic stability than similar esters. They have good detergent properties and are used in toilet soaps and shampoo formulations because of their low irritant properties.
Sulfate Ethers
The ether obtained when the fatty alcohol is ethoxylated still carries an end OH group, and from this point, the molecule is sulfated to obtain alcohol ether sulfates. The structure of this molecule is given below.
R (OCH 2 CH 2 ) n OSO 3 - M +
Figure: Structural Formula of Fatty Alcohol Ether Sulfates.
Since this class of surfactants has the potential to carry the advantages of both anionic and nonionic surfactants, it has developed very rapidly recently and has become widespread. Generally, ethoxylation of fatty alcohol is not long enough to be nonionic surfactant in water solubility, and only 5 or fewer ethylene oxide units are usually added to the molecule and the non-sulfated product is still not capable of water solubility. This water-insoluble nonionic substance is sulfated with chlorine sulfonic acid or SO 3 and is usually neutralized with sodium hydroxide to obtain the desired product. Other counter-ions are also obtained by lightly modifying the reaction or by alternative reactions.
R— (OCH 2 CH 2 -) n OH + SO 3 R— (OCH 2 CH 2 -) n OSO 3 HFigure: Sulfatation of Ethoxylated Alcohols with Sulfur Trioxide.
Sodium salts of ether sulfates have very low cloud points even at rather high concentrations. The fact that this group is easy to biodegrade, they are foam regulators in hard waters, they show less irritating properties to the eyes and skin, they increase water solubility, and that they can be produced with cheap raw material input has led to further research on them.
The starting materials are fatty alcohols. Fatty alcohols from vegetable and animal sources are expensive. The use of primary and secondary alcohols from petroleum products lowers the effluent costs of this group. They are sold as a colorless, odorless and liquid with approximately 25-60% active ingredient. If alcohol is added as a solvent, the viscosity of the solution decreases. The sulfate bond is sensitive to hydrolysis in hot acidic solution, hydrolysis very slowly in hot alkaline solution. Sulfated polyoxy ethylene alcohols are very foamy cleaning, wetting, emulsifying and dispersing reagents. They have a wide range of usage in dish detergents, shampoos, emulsion polymerization and textile processes.
Anionic surfactants can also be obtained by sulfating slightly ethoxylated alkyl phenols, as expressed by the general formula below.
RC 6 H 4 -O (CH 2 CH 2 O) n H
Figure: Structural Formula of Alkyl Phenol Ethoxylate.
Sulfated alkylphenol ethoxylates are used in toilet soap preparations, but have more effective use in mild domestic liquid detergent preparations.
phosphates
Phosphates are phosphoric acid based ester surfactants and form a very uniform group of anionic surfactants. The structural formula of the esters and diesters of phosphoric acid is given below.
RO-PO 3 - M +
Figure: General Formula of Phosphoric Acid Esters Based Surfactants.
Here the group R is usually a long chain alcohol or phenol. These substances can be obtained as free acids (M = H) or sodium or amine salts. In fact, they exist as a mixture of mono- and dibasic phosphates. Because of their low foaming properties, good solubility in water and many organic solvents and alkali hydrolysis resistant, it is stated that in some applications the same chemical structure has superior properties than sulfates and sulphonates. However; It is known that their performance as detergent is in many cases lower. The most common disadvantage of phosphate esters is that they are more expensive than sulfate and sulfonates. Wide solubility and activity limits of phosphoric acid esters in dry cleaning formulations,
Variation can be created to improve the properties of the alkyl phosphate surfactants, and a polyoxyethylene chain can be added between the alkyl and phosphate ester groups in the structure of the molecule. Such substances are known to acquire mild anionic character with slightly more common properties with nonionic analogues.
Alkyl phosphates and anionic surfactants based on alkyl ether phosphate are generally obtained by reaction of fatty alcohol or alcohol ethoxylate with a phosphorous agent such as phosphorus pentaoxide (P 4 O 10 ). A mixture of mono- and diesters of phosphoric acid is obtained as the reaction product. The ratio of this mixture depends on the rate of reactants and the amount of water in the reaction mixture. This reaction is given below.
He o
6 R-OH + P 4 O 10 2 ROP-OH + ROPOR OH OH
All commercial phosphate surfactants include both mono- and diesters of phosphoric acid. Proportional amounts of these vary from manufacturer to manufacturer. The physicochemical properties of alkyl phosphate surfactants depend on the ratio of esters. Phosphorus oxychloride (POCl 3 ) is also used as a phosphoring agent in the production of alkyl phosphates. When using phosphorus oxychloride, a mixture of mono- and diesters of phosphoric acid is obtained.
Fosfate surfactants are used in the metal industry and their anticorrosive properties are used. In addition, these substances are used as emulsifiers in plant protection preparations. Undiluted products are sold in the form of light colored, almost odorless, viscous liquid or soft wax. They are generally used as wetting, emulsifying, dissolving, dispersing, anti-corrosion, textile lubricant and antistatic protection agent. The products are used in dry cleaning detergents, anhydrous household cleaning detergents and cosmetic products, as emulsifiers in polymerization and in the composition of metal cutting or lubricating liquid.
ANNEX 1
CATIONIC SURFACE ACTIVE SUBSTANCES
Cationic surfactants constitute the third largest class of surfactants. Although it has some important exceptions, it is generally not compatible with anionics in terms of load character. Cationic surfactants with hydrolytic stability have high water toxicity. They are generally absorbed very strongly on many surfaces and are mainly used for in situ surface modification purposes.
Cationic surfactants have also increased their commercial importance due to the bacteriostatic properties detected in 1938. From this date; Although they do not have as much use as anionic substances in terms of economic value and total production amounts, hundreds of commercial products from cationic substances have been placed on the market. Today, cationic surfactants play an important role in cosmetic products as antiseptic agents, general fungicides and germites and in many chemical applications. II. Many new application areas for cationic surfactants have been developed since World War II. These surfactants are rather called specialty chemicals. Compared to other anionic and nonionic surfactants, it has an 8% share in the total surfactant market. However; With the emergence of new areas of use for these surfactants and the increased special requirements expected from surfactants, the economic significance of cationic surfactants is expected to increase in the future.
If the source of hydrophobic groups (R) in cationic surfactants is derived from natural oils such as coconut or tallow, the hydrophobic group varies in both chain length and degree of unsaturation of the alkyl chain. When the hydrophobic group is obtained from petrochemical sources; Differences can occur in terms of the components that make up the molecule, their molecular weights, their branching, cyclic impurities, and the location of ring-binding structures in aromatic derivatives.
Pure cationic surfactants such as cetyltrimethylammonium bromide (CTAB) are used extensively in basic surface activity physicochemistry research. Such research has led to major advances in understanding the basics of the behavior principles of surfactants. However, due to the significant differences in composition and purity between commercial and research quality materials, one should not overlook the effects of such differences in the behavior of a particular surfactant in a specific application.
Vegetable and animal oils were the only raw material source for cationic surfactants until the introduction of flat chain and petroleum-based products. All these substances can be regarded as oil amine derivatives containing one, two or three alkyl chains attached directly or indirectly to a cationic nitrogen group. The most important classes of these cationic surfactants are amine salts, quarterner ammonium compounds and amine oxides.
The vast majority of cationic surfactants are based on the cationic charge-bearing nitrogen atom. Both amine and quarterner ammonium based products are common. Amines function as surfactants in protonated state. Therefore, they are not used at high pH. On the other hand, quarterner ammonium compounds, that is, quats are not sensitive to pH. Non-quarterner cationics are also much more sensitive to polyvalent anions. As mentioned earlier, ethoxylated amines have the characteristic properties of both cationics and nonionics. The figure below shows the structures of typical cationic surfactants. The surfactant reported as the ester quat in this way represents a new environmentally friendly surfactant. These have largely replaced dialkyl quats as textile softening agents. The basic synthesis procedure for non-ester guarterner ammonium surfactants is done through nitrile. A fatty acid is reacted with ammonia at high temparature to give the appropriate nitrile. This nitrile is subsequently hydrogenated to the primary amine using cobald or nickel catalyst.
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ NH 3 +
Fatty amine salts
/ \ / \ / \ / \ / \ / \ / \ / \ / \ NH 2+ / \ / \ NH 3 +
Fat diamine salts
 |
/ \ / \ / \ / \ / \ / \ / \ / \ / \ N +
Alkyl "quat"
-H 2 O H 2
R-COOH + NH 3 RC Ξ N R-CH 2 NH 2 Secondary amines can either be obtained directly from nitrites or they occur from a primary reaction with a two-step reaction. Ammonia must be continuously evacuated from the reaction medium to support secondary amine formation on a single-step path, believed to continue over an intermediate.
RC Ξ N + R-CH 2 NH 2 + 2H 2 → (R-CH 2 ) 2 NH + NH 3
Primary amines can be converted to long chain 1,3-diamines by cyanoethylation.
H 2
R-CH 2 NH 2 + CH 2 = CHCN R-CH 2 NH (CH 2 ) 2 CN R-CH 2 NH (CH 2 ) 3 NH 2Primary and secondary long chain alkyl amines can be methylated to tertiary amines by reaction with formaldehyde under reducing conditions.
(R-CH 2 ) 2 NH + HCHO + H 2 (R-CH 2 ) 2 NCH 3Ethylene oxide can also be used as the alkylating agent to convert primary or secondary amines into tertiary amines. General structural formulas of these tertiary amines are given below.
R-CH 2 –N (CH 2 CH 2 OH) 2 and (R-CH 2 ) 2 NCH 2 CH 2 OH
Quarterner ammonium compounds are usually prepared from tertiary amines by reaction with a suitable alkylating agent such as methyl chloride, methyl bromide and dimethyl sulfate. These alkylating agents are taken into account in the selection of the counter ion of the surfactant.
(R-CH 2 ) 2 NCH 3 + CH 3 Cl (R-CH 2 ) 2 N + (CH 3 ) 2 Cl -Ester-containing quarterner ammonium surfactants, ie ester quats, are produced by esterification of a fatty acid (or fatty acid derivative) with an amino alcohol. This process is followed by N-alkylation as described above.
This process is described in the same manner as triethanol amine as amine alcohol and dimethyl sulfate as methylization agent.
H 2 O (CH 3 ) 2 SO 4
2R-COOH + N (CH 2 CH 2 OH) 3 (R-COOCH 2 CH 2 ) 2 NCH 2 CH 2 OH (R-COOCH 2 CH 2 ) 2 N + CH 2 CH 2 OH CH 3 SO 4
l
CH 3
Cationic surfactants have two important classes depending on the differences in the structure of the nitrogen-containing group. The first consists of alkyl nitrogen compounds such as at least one long chain alkyl group and simple ammonium salts containing one or more amine hydrogen, and quarterner ammonium compounds where all amine hydrogen is replaced with organic radicals. The substituents of amines can be either long or short chain alkyls, alkylaryls or aryls. The counter ion may be structures such as halide, sulfate and acetate. The second category includes heterocyclic substances characterized by pridinium, morpholinium and imidazolinium derivatives. Other cationic functional groups may be present, but their use is less than the other two main groups.
In pyridinium and other heterocyclic amine surfactants, their surfactant properties are provided by alkyl groups used to quarternize the amine. As a difference to this approach; to directly attach the surfactant long alkyl (or fluoroalkyl) group to the heterocyclic ring and quarternize the nitrogen with a short chain alky halide. General structural formulas of cationic surfactants are given below.
R- (CH 2 ) 5 NH + R'X - and R- (CH 2 ) 5 N + R ' 2 X -
The R groups in these formulas refer to the long chain hydrophobic group and the R 'groups refer to the short chain alkyl or hydroxyalkyl chain.
Some types of amphoteric surfactants, where nitrogen covalently bonds to anionic groups (eg - CH 2 CH 2 SO 3 - ) or potentially anionic (eg COOH) groups, are also classified as cationic surfactants in some sources.
Nitrogen-based compounds make up the vast majority of cationic surfactants. However, phosphonium, sulfonium and sulfoxonium surfactants are also available.
The first two of these are produced by treating trialkyl phosphine or dialkyl sulfur separately with alkyl chloride. This process is as shown below in phosphonium surfactants.
R 3 P + R ' X R 3 P + - R ' X - Sulfoxonium surfactants are obtained by hydrogen peroxide oxidation of sulfonium salts.
Due to the very different properties of cationic surfactants, their economic importance has increased in recent years. Many cationic surfactants are biologically active substances, as they have the ability to kill or inhibit microorganisms. They also have an important place in the textile industry as softeners, waterproofing agents and dye fixers.
CATIONICACTIVE SPECIES
Alkyltrimethylammonium chlorides (ATMAC) and smaller amounts of alkyltrimethylammonium bromides (ATMAB); They are mainly used in formulations of cosmetics, such as conditioners, hair dyes and other hair and personal care products. Hydrophobic alkyl chains of alkyltrimethylammonium chlorides (ATMAC) and alkyltrimethylammonium bromides (ATMAB) are normally linear. The structures of these surfactants are given below.
Figure… .: Structural Formula of Alkyltrimethylammonium Chloride and Bromide.
Here; R usually represents an alkyl chain of 12-18 carbon atoms and either a C1 - or Br - as X - counter ion .
2. Dialkyldimethylammonium salts
Dialkyldimethylammonium clumps (DADMAC) are used as antistatic agents in cosmetics including hair creams and hair coloring products. In addition; Dialkyldimethylammonium clumps (DADMAC) are used as biocides in industrial cleaning agents and to a lesser extent in the content of general purpose household cleaning agents. The alkyl chains of dialkyldimethylammonium clumps (DADMAC) are normally linear. However; Dialkyldimethylammonium clurches (DADMAC) with at least a single branched alkyl chain are also used. The structures of dialkyldimethylammonium clusters (DADMAC) are given below.
Figure… .. Structure of dialkyldimethylammonium cleavages (DADMAC).
Here; R usually represents an alkyl chain of 10-16 carbon atoms.
3. Alkyldimethylbenzylammonium salts :
Alkyldimethylbenzylammonium clumps (ADMBAC) and bromides (ADMBAB); They are used in cosmetics containing hair creams and hair dye products. In addition to its use as surfactants and antistatic agents, alkyldimethylbenzylammonium compounds function as biocides in various cosmetic and detergent products. When alkyldimethylbenzylammonium clumps (ADMBAC) are added to general purpose and special purpose cleaning agents, their biocidal properties are used. The structures of alkyldimethylbenzylammonium clumps (ADMBAC) are given as follows.
Figure…. The structure of the alkyldimethylbenzylammonium chloride (ADMBAC).
Here; R usually represents a linear alkyl chain of 8-18 carbon atoms and either a Cl - or Br - as X - counter ion .
4. Alkyl Ester Ammonium Salts:
In the last 10 years, alkyl ester ammonium salts have largely replaced dialkyldimethylammonium salts as a fabric softener in domestic surfactant use. Alkyl ester ammonium salts are quarterner ammonium compounds containing one or more rather two weak ester-bound structures to the molecular structure. This group of cationic surfactants consists of at least three different types of esters. These;
a) N-Methyl-N, N-bis [2 - (C 16-18 -acryloxy) ethyl] -N - (2-hydroxyethyl) ammonium methosulfate ester ester quat (EQ).
b) N, N, N-trimethyl-N- [ 1,2-di- (C 16-18 acyloxy) propyl] ammonium diesterquat (DEQ).
c) Diethyl ester dimethylammonium chloride (DEEDMAC) (Di- (tallow acid) ester of Di-2-hydroxyethyl dimethylammonium chloride).
Structures of alkyl ester ammonium salts are given as follows.
NONIONIC SURFACE ACTIVE SUBSTANCES
Surfactants that do not form charged particles when they dissolve or disperse in the aqueous environment, which depend on whether they have hydrophilic tendencies, whether they bond hydrogen with water molecules, are called "nonionic surfactants". They are formed by the combination of a long hydrophobic alkyl group and a high polarity neutral group or groups. The water-soluble group should have enough polarity to hold hydrophobic groups in the aqueous solution.
The chemical structure of nonionic surfactants has some advantages among other surfactants. Due to their electrically neutral structure, they show useful properties in chemical mixtures. This feature enables them to show less sensitivity to electrolytes in a chemical system. These surfactants offer high flexibility in synthesis processes, which is achieved by careful control of the size of the hydrophilic group during polymerization .
Nonionic surfactants have very compatible physical properties, which creates a wide range of applications for them. In response to market needs, a wide variety of nonionic surfactants have been developed in recent years. In addition to the previous conventional conventional ethoxylates, nonionic surfactants such as glycerol esters, amine oxides, acetylenic alcohol derivatives, silicones, fluorocarbons and carbohydrate derivatives have found useful use in a variety of end-user industries, from agricultural application chemicals to textiles. These; They can be regarded as nonionic surfactant types with particular properties.
Nonionic surfactants differ chemically from both cationics and anionic surfactants. Because in reality the molecules are uncharged. The molecule is formed from some other water-soluble molecule part, rather than a hydrophilic group charged part. Traditionally in nonionic surfactants, the hydrophilic group is polyoxy ethylene chains, and this poly (ethylene oxide) portion gives the molecule water-soluble properties. These polymers used in nonionic surfactants are typically 10-100 units long. Nonionic surfactants are two groups in terms of chemical structure. These;
a) Containing a polyether group,
b) Containing a polyhydroxyl group.
A large part of the nonionic surfactants group consists of polyether groups and the polar group consists of the oxyethylene unit formed by the polymerization of ethylene oxide. In fact, the "poly" prefix is a false definition here. While some surfactants, such as dispersers, have longer oxyethylene chains, the number of oxy ethylene units in the polar chain in these surfactants is between 5-10. Ethoxylation is usually carried out in alkaline conditions. Any substance containing an active hydrogen can be ethoxylated. The most commonly used starting materials are fatty alcohols, alkyl phenols, fatty acids and fatty amines. Esters, such as triglyceride oils, can be ethoxylated by a process involving alkali ester hydrolysis followed by ethoxylation of the acid and alcohol formed in the process. After this process, partial condensation of ethoxylated groups is performed. Castor oil ethoxylates used in animal feed applications are an interesting example of triglyceride-based surfactants.
The most important groups that provide water solubility in nonionic surfactants are polyols and ether bonds. In addition, nonionic surfactants can also contain hydrophilic ester and amide bonds in their structures. Nonionic polyether based surfactants; In the substrate expressed with RXH, when R is a long hydrocarbon chain and X is a bonded group such as -O- or -COO-, it is the structural structure obtained by its interaction with ethylene oxide.
RXH + nH 2 C ---- CH 2 RX (OCH 2 CH 2 ) n H HE IS
This reaction is called "ethoxylation reaction". Chain length of oxyethylene; It is regulated by both the properties of RXH and ethoxylation conditions. The two most common classes of nonionic surfactants that carry the poly (ethylene oxide) unit as the hydrophilic group are alcohol ethoxylates and alkyl phenol ethoxylates. The figure below ………. In acol ethoxylates and the structure of alkyl phenol ethoxylates are schematized.
Figure… .. Akol ethoxylates and the chemical structure of Alkyl Phenol ethoxylates. The poly (ethylene oxide) chain forms the head of the water-soluble surfactant molecule.
Nonionic surfactants are liquid and solid waxes. Due to their properties, they change some important properties of the loaded surfactant. When they are at the same concentration as the charged surfactant, they further reduce the surface tension and give a lower CMC value. This is because; The electrical impulse that occurs between the polar groups of charged surfactants located either in the interface or in the micelles is not caused by nonionic surfactants that absorb more easily in the interface and cluster in the micelle. If the polyoxy ethylene groups in these surfactants are transferred to an organic compound with any reactive hydrogen, the organic substance can be dissolved. Dissolution of polyoxy ethylene solubilized product -CH 2 CH 2 -O-CH 2 CHPolyoxy, such as 2 -O-, is bound to ether bonds in the ethylene chain. Also; The hydrophilic strength of a polyoxy ethylene (-CH 2 CH 2 O-) is approximately one methylene (-CH 2-) is equal to the hydrophobic force of the unit. The solubility of polyoxy ethylene surfactants in water decreases with increasing temperature. It appears that the solution becomes cloudy at a temperature called cloud point. This event; It is due to the decrease in the degree of hydration or the growth of the micelle size at temperatures higher than the cloud point and occurs as a second phase. At temperatures lower than the cloud point, most nonionic surfactants are water miscible. The cloud point of the nonionic surfactant depends on the structure of the hydrophobic group and the number of oxyethylene units, charged surfactants such as anionic surfactant in the medium. To absorb longer hydrophobe chains into water, an excess oxyethylene unit is required in the solution. For example, the n-decyl chain is water-soluble with three oxyethylene units, and four oxyethylene units are needed for the same chain, which is water miscible at room temperature. Dissolution in the n-hexadecyl chain occurs in 5-6 units.
In environments with high sodium ions, the solubility of polyoxyethylene decreases. However, HCl and Ca ++ ions increase solubility, that is, it is not affected by hard water. Nonionic surfactants dissolve iodine in aqueous solution and reduce the toxic effect on human but do not weaken biological activity. Polyoxyethylene surfactants. They give moderate foam.
Examples of polyhydroxyl (polyol) based surfactants are sucrose esters, sorbitan esters, alkyl glycosides and polyglycerol esters. The most recently considered species is actually a combination of polyol and polyether surfactants. Polyol surfactants can also be ethoxylated. Fatty acid esters of sorbitan and similar ethoxylated products are the most common example. During production, the five-membered ring structure of the sorbitan is created by dehydration of sorbitol. Sorbitan ester surfactants are edible products and are therefore used in food and drug applications.
Another class of nonionic surfactants are alkyl polyglycosides. For at least the past 20 years, these have been recognized as new generation nonionic surfactants. In these molecules, the hydrophilic group is sugar, in which case the molecule is polysaccharide. But these are also made up of disaccharides, trisaccharides, maltose and various other sugars.
Figure…: Structures of alkyl polyglycosides; the structure of an alkyl glycoside and a glucose ester.
Although these are called polyglycosides; They usually contain only one or two sugar groups on the chain.
Sorbitan esters are also commercially important surfactants of this group. Moderate harsh conditions are required for their synthesis. For example, synthesis conditions such as 225-250 ° C are used in an acid catalyst.
Acetylenic glycols, namely surfactants containing acetylenic bonds and hydroxyl groups located centrally at adjacent carbon atoms, constitute a special type of hydroxyl-based surfactant that has found use as anti-foaming agents, especially in coating applications. Figure 1.7. shows the structures of the most commonly used non-ionic surfactants. Fatty acid ethoxylates are particularly complex mixtures of high amounts of polyethylene glycol and fatty acid as a by-product. The only major type of non-ionic surfactant is fatty alcohol ethoxylates. These are used in liquid and powder detergents as well as in industrial applications. These are particularly useful for stabilizing O / W emulsions. Oil alcohol ethoxylates pH:
Ethoxylation Reactions:
Ethoxylation reaction; The substrate itself, by basic or acidic catalysis, or amine, is the reaction of ethylene oxide with basic substrates. In ethoxylation with basic catalyst, the base is directed to the RXH substrate first. RXH alkyl phenol will form strong nucleophile and ethylene phenoxide formed with the base. NaOH, NaOCH 3 and KOH are used as the base . The base used is usually 0.005-0.05 molds per mole of hydrophobic material.
Figure
Figure
If ethylene oxide is added, alkoxide containing two oxyethylene are obtained. The polyoxy ethylene chain can be extended as desired.
Figure
Since the phenol is more acidic than the first ethoxymer, the reaction will continue as above. The reaction will be present only in suitable reaction conditions as the phenoxide ion as follows. Different reactivity between alkoxides slows down the incorporation of ethylene oxide initially, and accelerates the more reactive alkoxide ethoxylation reaction.
Figure
If RXH is a long chain primary or secondary alcohol, similarly ethoxylated alcohol will be obtained. Long chain alcohols are obtained from the previously described ethylene telomerization, hydroformulation process and reduction of oils. Primary alcohols are less acidic than polyoxy ethylene derivatives. Alcohol-compatible alkoxide and its derivatives have very close nucleophilicity. Therefore, they can be ethoxylated with basic catalysts.
Secondary alcohols behave differently. It is important to obtain secondary alcohol raw material for nonionics. N 2 5% O 2 with the air oxidation of 165 o C and boric acid C 10-15 are derived from n-paraffin.
Figure
R and R 'are n-alkyl groups.
Nonionic Products:
Nonionic surfactants are divided into four subgroups.
- Alkyl phenol ethoxylates
- Aliphatic alcohol ethoxylates
- Carboxylic esters
- Carboxylic amides
The most commonly used of alkyl phenol ethoxylates are nonyl- and dodecyl-phenoxy poly (oxyethylene) ethanol. Elements of this group are propylene dimer, trimer, tetramer or more branched phenols. Branched alkyl groups have been replaced by linear alkyl groups in recent years. The aromatic character of ethoxylated C 8-12 alkyl phenols is weaker. They are dull yellow or colorless liquids. As their polyoxyethylene content increases, their viscosity increases. Their solubility in water increases as the amount of polyoxyethylene increases. To be fully miscible with water, they must contain 60% by weight of polyoxyethylene. Surface activity activities do not change in hard water.
Usage areas of polyoxyethylene alkyl phenols depending on their polyoxyethylene content;
- Alkyl phenols containing 20-40% polyoxy ethylene as an antifoam in surfactant solution
- Alkyl phenols containing 40-60% polyoxy ethylene as oil-soluble detergents, dispersants and emulsifiers
- Alkyl phenols with 60-70% polyoxyethylene content are used as auxiliary agents in textile processes and cleaners, as pulp production and as emulsifiers in acidic and basic media cleaners.
- Alkyl phenols containing 70-80% polyoxy ethylene, high temperature resistant wetting and cleaning agent, emulsifier for oil and waxes
- Alkyl phenols with 80-95% polyoxy ethylene content are used as stabilizers in synthetic rubber, emulsifying in vinyl acetate and acrylic polymerization, as coloring auxiliary.
The hydrophobes of ethoxylated aliphatic alcohols arestraight chain alcohols in theC 12-18 range and contain 1-50 moles of ethylene oxide. Undiluted products vary from liquid to wax depending on the ethylene content. They are dull yellow. As polyoxyethylene increases, there is slight coloration, and water solubility increases. The content of 65-70% polyoxyethylene provides complete mixing with water at room temperature. Solubility in aliphatic solvent is more than polyoxy ethylene alkyl phenols.
The ethoxylation rates of primary alcohols are higher than those of alkyl phenols. Also, the rate of ethoxylation of alcohols is primary> secondary> tertiary.
Carboxylic esters are compounds that contain polyol, polyoxy ethylene or both groups in the hydrophobic group. Glycerin fatty acid esters, mono or di glyceride of saturated or unsaturated fatty acids, increase the aggregation of all other soluble surfactants. Theyhave a melting point between25-85 ° C and 1-mono-glycerides melt at higher temperatures than 2-glycerides.
Ethoxylated natural oils and waxes are also nonionic. The most used oil as raw material is castor oil, to a lesser extent, lanolin derivatives are also used. Castor oil contains high amounts of esterified rikin oleic acid. Ethoxylation at 60-70% takes place by alkaline catalysis. The product formed is water soluble.
Ethoxylated castor oil is hydrophilic emulsifier, dispersing and lubricant. It is used as an auxiliary agent in the processing of leather products.
Lanolin alcohols are made from oil from raw sheep wool. They are a mixture of cholestrol, isocollestrol and other high alcohols.
Polyethylene derivatives of fatty acid esters are produced as mono or di ester. Production is done by changing the molecular weight of the polyethylene: fatty acid ratio or acid esterified polyglycol. They are liquid or wax based on their polyethylene content. They generally have softening and lubricating properties. The content of 60% polyoxy ethylene by weight stabilizes the saturated fatty acids in the water at room temperature and reduces the surface tension.
They are obtained by esterification of ethylene oxide and fatty acid or polyethylene glycol and fatty acid with acid catalyst.
Anhydrosorbitol fat esters are not strong hydrophilic groups, they are insoluble in water, but are quite well soluble in fatty acids.
Figure
They are obtained by direct esterification of sorbitol from fatty acids with acid catalyst at 225-250 o C. Ethoxylation can be applied to the esters to provide better hydrophilic property.
Carboxylic amides: mono and di ethanol are produced as amine condensates.
A mole of an alkanol amine such as di ethanol amine and 1 mole of fatty acid are mixed and heated, an exothermic reaction produces 90% 1/1, (amine / acid) super, 7% non-convertable ethanol amine.
They do not have cleaning properties, they only disperse in water and dissolve in detergent solution. Therefore, they are found in anionic detergents as strong foam controllers and thickeners.
Zwitter Ionic Surfactants:
Zwitter ionic surfactants contain groups with two different charges. While the positively charged of these groups is mostly ammonium, negatively charged groups may have been obtained from a variety of sources, but the most commonly used are carboxylates. Although Zwitter ionics are generally known as “amphoteres”, as mentioned earlier, these terms do not have exactly the same meanings. When going from low pH to high pH regions, while an amphoteric surfactant has a net cationic charge, they go from here towards the zwitter ionic and net anionic charge, but the surfactant has a zwitter ionic charge only in a certain pH range.
The literally varying loads of amphoteric surfactants affect pH, such as soaping, wetting and detergent properties. All these features are closely related to the pH of the solution. The physicochemical behavior of this type of surfactant at the isoelectric point is generally similar to that of nonionic surfactants. A slow change (transition) between cationic and anionic charges is observed below and above the isoelectric point.
N-alkyl derivatives of simple amino acids such as glycine (NH 2 CH 2 COOH), Betaine ((CH 3 ) 2 NCH2COOH) and aminopropionic acid (NH 2 CH 2 CH 2 COOH) form a common type of zwitter ionic surfactants. Although they are usually derived from amino acids, a long chain amine and an acrylic acid derivative or sodium chloroacetate compounds can also react to form one and two carbon structures, respectively, between the nitrogen and carboxyl groups. As an example; The reaction of alkyldimethyl amine and sodium monochloroacetate can yield a typical betaine surfactant.
CH 3 CH 3
│ │
RN + ClCH 2 COO - Na + RN + -CH 2 COO + NaCl │ │
CH 3 CH 3
Amidobetaines are synthesized analogously from an amidoamine.
CH 3 CH 3
│ │
RCONH (CH 2 ) 3 -N + ClCH 2 COO - Na + RCONH (CH 2 ) 3 -N + -CH 2 COO - + NaCl │ │
CH 3 CH 3
Another common type of Zwitter ionic surfactants are imidazoline compounds obtained by reacting fatty acids with chloroacetate with aminoethylethanolamine. There may be some confusion in the scientific nomenclature of this type of surfactant; because these products are generally thought to contain an imidazoline ring, but according to information from recent studies, the five-membered ring synthesis is broken down in the second step of the reaction. A typical reaction is shown as follows:
R-COOH + H 2 NCH 2 CH 2 NH CH 2 CH 2 OH Zwitter ionic surfactants are characterized by their excellent dermatological properties. Also, their damage to eye tissues is low, so they are used in the production of shampoos and other cosmetics. Because they do not have any net charge, they are used successfully in high electrolyte formulations, showing similarity with nonionic surfactants. These are traditionally used to formulate alkaline cleaners. Examples of typical zwitter ionic surfactants are given in Figure 1.11, and general information about such surfactants is given in Table 1.7. Amine oxide surfactants - or, more accurately, N-oxides of tertiary amines - are sometimes classified as zwitter ionic, sometimes nonionic, and sometimes cationic. They have a formal charge separation in nitrogen and oxygen atoms. The basic behavior of these structures is like nonelectrolytes, but at low pH or in an environment with anionic surfactants, they capture a proton from cationic conjugated acids. A salt of 1: 1 structure is present in highly surfactant form in the form of anionic surfactant-protonated aminoxide and its salt. Aminoxides are obtained by oxidation of a suitable tertiary amine with hydrogen peroxide.
N + -CH 2 COO - Betaine
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