Nomenclature and isomerism. Soaps and detergents

The main constituent part of animal and vegetable fats are esters of trihydric alcohol - glycerol and fatty acids, called glycerides(acylglycerides). Fatty acids are found not only in glycerides, but also in most other lipids.

The variety of physical and chemical properties of natural fats is due to the chemical composition of fatty acids of glycerides. Fat triglycerides contain various fatty acids. Moreover, depending on the type of animal or plant from which the fats are obtained, the fatty acid composition of triglycerides is different.

The composition of glycerides of fats and oils consists mainly of high molecular weight fatty acids with the number of carbon atoms 16.18, 20.22 and higher, low molecular weight with the number of carbon atoms 4, 6 and 8 (butyric, caproic and caprylic acids). The number of acids isolated from fats reaches 170, but some of them are still insufficiently studied and information about them is very limited.

Natural fats contain saturated (saturated) and unsaturated (unsaturated) fatty acids. Unsaturated fatty acids can contain double and triple bonds. The latter are very rare in natural fats. As a rule, natural fats contain only monobasic carboxylic acids with an even number of carbon atoms. Dibasic acids are isolated in small amounts in some waxes and fats exposed to oxidizing agents. The overwhelming majority of fatty acids in fats have an open chain of carbon atoms. Branched-chain acids are rare in fats. Such acids are found in some waxes.

Fatty acids of natural fats are liquid or solid, but fusible substances. High molecular weight saturated acids are solid, most of the unsaturated fatty acids of normal structure are liquid substances, and their positional and geometric isomers are solid. The relative density of fatty acids is less than one and they are practically insoluble in water (with the exception of low molecular weight). In organic solvents (alcohol, ethyl and petroleum ethers, benzene, carbon disulfide, etc.) they dissolve, but with an increase in molecular weight, the solubility of fatty acids decreases. Hydroxy acids are practically insoluble in petroleum ether and cold gasoline, but they are soluble in ethyl ether and alcohol.

Of great importance in the refining of oils and in soap making is the reaction of interaction of caustic alkalis and fatty acids - the reaction of neutralization. The action of sodium or potassium carbonate on fatty acids also produces an alkaline salt or soap with the release of carbon dioxide. This reaction takes place during the cooking of soap during the so-called carbonate saponification of fatty acids.

Fatty acids of natural fats, with rare exceptions, belong to the class of monobasic aliphatic carboxylic acids having the general formula RCOOH. In this formula, R is a hydrocarbon radical that can be saturated, unsaturated (of varying degrees of unsaturation) or contain a group - OH, COOH - carboxyl. Based on X-ray structural analysis, it has now been established that the centers of carbon atoms in the chain of fatty acid radicals are spatially located not in a straight line, but in a zigzag pattern. In this case, the centers of all carbon atoms of saturated acids are located on two parallel straight lines.

The length of the hydrocarbon radical of fatty acids affects their solubility in organic solvents. For example, the solubility at 20 ° C in 100 g of anhydrous ethyl alcohol of lauric acid is 105 g, myristic acid is 23.9 g, and stearic acid is 2.25 g.

Fatty acid isomerism. Isomerism is understood as the existence of several chemical compounds of the same composition and the same molecular weight, but differing in physical and chemical properties. There are two main types of isomerism: structural and spatial (stereoisomerism).

Structural isomers differ in the structure of the carbon chain, the arrangement of double bonds and the arrangement of functional groups.

Examples of structural isomers are compounds:

a) different in structure of the carbon chain: normal butyric acid CH 3 CH 2 CH 2 COOH; isobutyric acid

b) different in the arrangement of double bonds: oleic acid CH 3 (CH 2) 7 CH = CH (CH 2) 7 COOH; petroselinic acid CH 3 (CH 2) 10 CH = CH (CH 2) 4 COOH; vaccenic acid CH 3 (CH 2) 5 CH = CH (CH 2) 8 COOH.

Spatial isomers, or stereoisomers, with the same structure, differ in the arrangement of atoms in space. This type of isomers includes geometric (cis and trans isomers) and optical. Examples of spatial isomers are:

a) geometric isomers: oleic acid having the cis form

transformed elaidic acid

b) optical isomers:

lactic acid CH 3 CHONSOOH;

glyceraldehyde CH 3 ONSNONSNO;

ricinoleic acid CH3 (CH 2) 5 CHONCH 2 CH = CH (CH 2) 7 COOH.

All of these optical isomers have asymmetric (active) carbon marked with an asterisk.

Optical isomers rotate the plane of polarization of light by the same angle in opposite directions. Most of the natural fatty acids have no optical isomerism.

In natural fats that have not undergone oxidative processes, unsaturated fatty acids are mainly cisconfigured. The geometric cis and trans isomers of unsaturated fatty acids differ significantly in their melting points. Cisisomers melt at a lower temperature than trans isomers. This is clearly illustrated by the reaction of cis-transconversion of liquid oleic acid into solid elaidic acid (melting point 46.5 ° C). This hardens the fat.

The same transformation occurs with erucic acid, which transforms into a solid trans-isomer - brassidic acid (melting point 61.9 ° C), as well as ricinoleic acid, which transforms into a trans isomer - racinelaidic acid (melting point 53 ° C).

Polyunsaturated fatty acids (linoleic, linolenic) do not change their consistency during this reaction.

In natural fats that have not undergone oxidative processes, the following main homologous groups of fatty acids are found:

1. Saturated (saturated) monobasic acids.

2. Unsaturated (unsaturated) monobasic acids with one, two, three, four and five double bonds.

3. Saturated (limiting) hydroxy acids.

4. Unsaturated (unsaturated) hydroxy acids with one double bond.

5. Dibasic saturated (saturated) acids.

6. Cyclic acids.

Esters can be considered as derivatives of acids in which the hydrogen atom in the carboxyl group is replaced by a hydrocarbon radical:

Nomenclature.

Esters are named after acids and alcohols, the residues of which are involved in their formation, for example H-CO-O-CH3 - methyl formate, or methyl formic acid; - ethyl acetate, or ethyl acetate.

Methods of obtaining.

1. Interaction of alcohols and acids (esterification reaction):

2. Interaction of acid chlorides and alcohols (or alkali metal alcoholates):

Physical properties.

Esters of lower acids and alcohols are liquids lighter than water, with a pleasant odor. Only esters with the lowest number of carbon atoms are soluble in water. Esters are well soluble in alcohol and distil ether.

Chemical properties.

1. Hydrolysis of esters is the most important reaction of this group of substances. Hydrolysis by water is a reversible reaction. To shift the equilibrium to the right, alkalis are used:

2. Reduction of esters with hydrogen leads to the formation of two alcohols:

3. Under the action of ammonia, esters are converted into acid amides:

Fats. Fats are mixtures of esters formed by the trihydric alcohol glycerol and higher fatty acids. General fat formula:

where R - radicals of higher fatty acids.

Most often, the composition of fats includes the saturated acids palmitic and stearic and unsaturated acids oleic and linoleic

Getting fats.

At present, only the production of fats from natural sources of animal or vegetable origin is of practical importance.

Physical properties.

Fats formed by saturated acids are solids, and unsaturated ones are liquid. All are very poorly soluble in water, well soluble in diethyl ether.

Chemical properties.

1. Hydrolysis, or saponification of fats occurs under the action of water (reversible) or alkalis (irreversible):

Alkaline hydrolysis produces higher fatty acid salts called soaps.

2. Hydrogenation of fats is the process of adding hydrogen to the residues of unsaturated acids that make up fats. In this case, the residues of unsaturated acids pass into the residues of saturated acids, and the fats from liquid to solid.

Of the most important nutrients - proteins, fats and carbohydrates - fats have the highest energy reserves.

Chapter 30. COMPLEXES. FATS

Soaps and detergents. Sodium and potassium salts of higher fatty acids are called soaps, because they have good detergent properties. Sodium salts form the basis of solid soaps, while potassium salts form the basis of liquid soaps. They are obtained by boiling tallow or vegetable oil with sodium or potassium hydroxide - hence the old name for alkaline hydrolysis of fats - "saponification". The cleansing (washing) properties of soap are explained by the wetting ability of soluble salts of higher fatty acids, i.e. soap anions have an affinity for both greasy dirt and water. The anionic carboxy group has an affinity for water: it is hydrophilic. The hydrocarbon chain of a fatty acid has an affinity for fatty contaminants. It represents the hydrophobic end of the soap molecule. This end dissolves in a drop of dirt, resulting in its transformation and transformation into a micelle. Removal of "foamy" micelles from the contaminated surface is achieved by washing it with water.

In the so-called tough water containing Ca 2+ and Mg 2+ ions, the detergency of soap decreases, since, interacting with calcium and magnesium ions, soaps form insoluble calcium and magnesium salts, for example:

As a result, the soap forms flakes on the surface of the water instead of foam and is wasted. They are deprived of this disadvantage synthetic detergents(detergents), representing by myself sodium salts various sulfonic acids general formula:

Common synthetic detergents (detergents) are alkylbenzenesulfonates:

True, the widespread use of synthetic detergents (washing powders) creates its own problems. A typical laundry detergent contains approximately 70% synthetic detergent and approximately 30% inorganic phosphates. Phosphates remove soluble calcium salts. Unfortunately, these phosphates end up in wastewater, which is discharged into streams, rivers, lakes or oceans. Phosphates are a breeding ground for certain algae. This leads to a strong overgrowth of cyanobacteria, especially in enclosed bodies of water, for example, in lakes.

Among the functional derivatives of carboxylic acids, a special place is occupied by esters- compounds representing carboxylic acids, in which the hydrogen atom in the carboxyl group is replaced by a hydrocarbon radical. General formula of esters

An ester molecule consists of an acid residue (1) and an alcohol residue (2).

The names of esters are derived from the name of the hydrocarbon radical and the name of the acid, in which the suffix "at" is used instead of the ending "-oic acid", for example:

Esters are often named after the residues of acids and alcohols of which they are composed. So, the esters considered above can be called: ethyl acetate, croton methyl ether.

Esters are characterized by three types of isomerism: 1. Isomerism carbon chain, begins with an acid residue with butanoic acid, with an alcohol residue with propyl alcohol, for example:

2. Isomerism ester grouping provisions - CO – O–. This type of isomerism begins with esters, the molecules of which contain at least 4 carbon atoms, for example:

3. Interclass isomerism, For example:

For esters containing unsaturated acid or unsaturated alcohol, two more types of isomerism are possible: isomerism of the position of the multiple bond and cis-trans isomerism .

Nomenclature and isomerism

An ester molecule consists of an acid residue (1) and an alcohol residue (2).

The names of esters are derived from the name of the hydrocarbon radical and the name of the acid, in which the suffix "at" is used instead of the ending "-oic acid", for example:

Esters are often named after the residues of acids and alcohols of which they are composed. So, the esters considered above can be called: ethyl acetate, croton methyl ether.

Esters are characterized by three types of isomerism: 1. Isomerism carbon chain, begins with an acid residue with butanoic acid, with an alcohol residue with propyl alcohol, for example:

2. Isomerism ester grouping provisions - CO – O–. This type of isomerism begins with esters, the molecules of which contain at least 4 carbon atoms, for example:

3. Interclass isomerism, For example:

For esters containing unsaturated acid or unsaturated alcohol, two more types of isomerism are possible: isomerism of the position of the multiple bond and cis-trans isomerism .

Physical properties

Esters of lower carboxylic acids and alcohols are volatile, slightly soluble or practically water-insoluble liquids. Many of them have nice smell. So, for example, HCOOC 2 H 5 - the smell of rum, HCOOC 5 H 11 - cherries, HCOOC 5 H 11 -iso - plums, СН 3 СООС 5 Н 11 -iso - pears, С 3 Н 7 СООС 2 Н 5 - apricot, С 3 Н 7 СООС 4 Н 9 - pineapple, С 4 Н 9 СООС 5 Н 11 - apples, etc.

Esters generally have a lower boiling point than their corresponding acids. For example, stearic acid boils at 232 ° C, and methyl stearate at 215 ° C. This is explained by the fact that there are no hydrogen bonds between the ester molecules.

Esters of higher fatty acids and alcohols are waxy substances, odorless, insoluble in water, readily soluble in organic solvents. For example, beeswax is mainly myricyl palmitate (C 15 H 31 COOC 31 H 63)

Chemical properties

1. Hydrolysis or saponification reaction.

Reaction esterification is reversible, therefore, in the presence of acids, a reverse reaction will occur, called hydrolysis, as a result of which the original fatty acids and alcohol are formed:

The hydrolysis reaction is accelerated by the action of alkalis; in this case, hydrolysis is irreversible:

since the resulting carboxylic acid forms a salt with alkali:

2. Addition reaction.

Esters containing unsaturated acid or alcohol are capable of addition reactions. For example, in catalytic hydrogenation, they add hydrogen.

3. Recovery reaction.

The reduction of esters with hydrogen leads to the formation of two alcohols:

4. Reaction of amide formation.

Under the action of ammonia, esters are converted to acid amides and alcohols:

The mechanism of the esterification reaction. Consider, as an example, the preparation of ethyl ester of benzoic acid:

Catalytic action sulfuric acid is that it activates the carboxylic acid molecule. Benzoic acid is protonated at the oxygen atom of the carbonyl group (the oxygen atom has a lone pair of electrons, due to which a proton is attached). Protonation leads to the conversion of a partial positive charge on the carbon atom of the carboxyl group into a full one, to an increase in its electrophilicity. Resonant structures (in square brackets) show the delocalization of the positive charge in the formed cation. The alcohol molecule, due to its lone pair of electrons, is attached to the activated acid molecule. The proton from the remainder of the alcohol moves to the hydroxyl group, which in this case turns into a "well-leaving" group H 2 O. After that, a water molecule is split off with a simultaneous release of a proton (catalyst return).

Esterification– reversible process. The direct reaction is the formation of an ester, the reverse is its acid hydrolysis. In order to shift the equilibrium to the right, it is necessary to remove water from the reaction mixture.

Fats and oils

Among the esters, a special place is occupied by natural esters - fats and oils, which are formed by the trihydric alcohol glycerol and higher fatty acids with an unbranched carbon chain containing an even number of carbon atoms. Fats are found in plant and animal organisms and play an important biological role. They serve as one of the energy sources of living organisms, which is released during the oxidation of fats. General fat formula:

where R ", R" ", R" "" are hydrocarbon radicals.

Fats are "simple" and "mixed". The composition of simple fats contains the remains of the same acids (ie R "= R" "= R" ""), the composition of mixed fats contains different ones.

The following fatty acids are most commonly found in fats:

Alkane acid

Butyric acid CH 3 - (CH 2) 2 -COOH

Caproic acid CH 3 - (CH 2) 4 -COOH

Caprylic acid CH 3 - (CH 2) 6 -COOH

Capric acid CH 3 - (CH 2) 8 -COOH

Lauric acid CH 3 - (CH 2) 10 -COOH

Myristic acid CH 3 - (CH 2) 12 -COOH

Palmitization acid CH 3 - (CH 2) 14 -COOH

Stearic acid CH 3 - (CH 2) 16 -COOH

Arachidic acid CH 3 - (CH 2) 18 -COOH

Alkenes acid

Oleic acid

Alkadiene acid

Linoleic acid

Alcatriene acid

Linolenic acid

Natural fats are a mixture of ethers and mixed esters.

According to their state of aggregation at room temperature, fats are divided into liquid and solid. The aggregate state of fats is determined by the nature of the fatty acids. Solid fats, as a rule, are formed by saturated acids, liquid fats (often called oils) - unsaturated. The higher the fat content, the higher the fat melting point. It also depends on the length of the fatty acid hydrocarbon chain; the melting point increases with the length of the hydrocarbon radical.

The composition of animal fats predominantly includes saturated acids, while vegetable fats contain unsaturated ones. Therefore, animal fats are usually solids, and vegetable fats are most often liquid (vegetable oils).

Fats are soluble in non-polar organic solvents (hydrocarbons, their halogen derivatives, diethyl ether) and insoluble in water.

1. Hydrolysis, or saponification of fats occurs under the action of water (reversible) or alkalis (irreversible):

Alkaline hydrolysis produces higher fatty acid salts called soaps.

2. Hydrogenation of fats is called the process of adding hydrogen to the residues of unsaturated acids that make up fats. In this case, the residues of unsaturated acids pass into the residues of saturated acids, and fats from liquid to solid:

3. Liquid fats (oils containing oleic, linoleic and linolenic acids), interacting with atmospheric oxygen, are able to form solid films - "Crosslinked polymers". Such oils are called "drying oils". They serve as the basis for natural drying oils and paints.

4. During long-term storage under the influence of moisture, air oxygen, light and heat, fats acquire an unpleasant odor and taste. This process is called "Rancid". Unpleasant smell and taste are caused by the appearance of products of their conversion in fats: free fatty acids, hydroxyacids, aldehydes and ketones.

Fats play an important role in human and animal life. They are one of the main sources of energy for living organisms.

Fats are widely used in the food, cosmetic and pharmaceutical industries.

Chapter 31. CARBOHYDRATES (SUGAR)

Carbohydrates are natural organic compounds with the general formula C m (H 2 O) n ( t, n> 3). Carbohydrates are classified into three large groups: monosaccharides, oligosaccharides and polysaccharides.

Monosaccharides are carbohydrates that cannot be hydrolyzed to form simpler carbohydrates.

Oligosaccharides are condensation products of a small number of monosaccharides, for example, sucrose - C 12 H 22 O 11. Polysaccharides (starch, cellulose) are formed by a large number of monosaccharide molecules.

Monosaccharides

Nomenclature and isomerism

The simplest monosaccharide is glyceraldehyde, C 3 H 6 O 3:

The remaining monosaccharides, according to the number of carbon atoms, are subdivided into tetroses (C 4 H 8 O 4), pentoses (C 5 H 10 O 5) and hexose (C 6 H 12 O 6). The most important hexoses are glucose and fructose. All monosaccharides are bifunctional compounds, which include an unbranched carbon skeleton, several hydroxyl groups and one carbonyl group. Monosaccharides with an aldehyde group are called aldoses and with a keto group - ketosis . Below are the structural formulas of the most important monosaccharides:

All of these substances contain three or four asymmetric carbon atoms, so they exhibit optical activity and can exist as optical isomers. The sign in brackets in the name of the carbohydrate denotes the direction of rotation of the plane of polarization of light: (-) denotes left-handed rotation, (+) - right-handed rotation. The letter D in front of the rotation sign means that in all these substances the asymmetric carbon atom farthest from the carbonyl group has the same configuration (i.e., the direction of bonds with substituents) as glyceraldehyde, the structure of which is given above. Opposite carbohydrates belong to the L-row:

Note that the D- and L-row carbs are mirror images of each other. Most natural carbohydrates are D-series.

It was found that in the crystalline state, monosaccharides exist exclusively in cyclic forms. For example, solid glucose is usually in the α-pyranose form. When dissolved in water, α-glucopyranose is slowly converted to other tautomeric forms until equilibrium is established. This is a kind of ring-chain tautomeric system.

Isomers are compounds that have an identical chemical composition, but a different molecular structure. Isomerization of fats and oils can occur in several ways:

Isomerism by position in triglncerida. This type of isomerism is a rearrangement of fatty acids in a glycerol molecule. This rearrangement usually occurs during transesterification, but can also occur during thermal exposure. Changing the position of the fatty acid in triglceride can affect crystal shape, melting characteristics, and lipid metabolism in the body.

Isomerism of the state. Unsaturated fatty acids can be isomerised in acidic or alkaline environments, as well as when exposed to high temperatures by migration of the double bond from positions 9 and 12 to others, for example, positions 9 and 10, 10 and 12 or 8 and 10. Nutritional value when transported double bond pa the new position is lost, fatty acids cease to be essential.

Spatial isomerism, a double bond can have two configurations: cis- or trans-form. Natural fats and oils usually contain cis-n-isomers of fatty acids, which are the most reactive and require relatively little energy to convert to trans isomers. Trans isomers are characterized by tighter molecular packing, allowing them to behave like saturated fatty acids with a high melting point. From the point of view of nutritional hygiene, trans fatty acids are considered analogs of saturated fatty acids, both types of compounds can cause an increase in LDL cholesterol in the circulatory system. 7ryang-zhnrnye acids are formed at very high temperatures, mainly during hydrogenation, and to a lesser extent - during deodorization. The content of / lryans-isomers in hydrogenated soybean and rapeseed oils can reach 55%, the isomers are represented mainly by trans-elaidic (C,.,) Acid, since almost all linolenic (C1v.3) and linoleic (C, x 2) acids hydrogenated to fatty acids C) K |. Isomerism due to thermal exposure, especially affecting linolenic

18 "h) acid and, to a lesser extent, on the fatty acid Clg 2, depends on the temperature and duration of exposure. In order for the formation of tRNC isomers not to exceed 1%, the deodorization temperature should not exceed 240 ° C, the duration of treatment is 1 hour, higher temperatures can> be used with shorter exposure times.

Conjugated linoleic fatty acids (CLA). CLA is a natural isomer of linoleic acid (C | R 2), in which two double bonds are conjugated and located at carbon atoms 9 and 11 or 10 and 12, with a possible combination of cis and trans isomers. CI.A is usually a producer. is an anaerobic bacteria of the rumen of cattle during biohydrogenation. Modern international medical research has shown that CLA may have health-promoting properties such as anti-tumor 1 and anti-atherogenic 2.