10.5. Complex ethers. Fats

Esters- functional derivatives of carboxylic acids,
in the molecules of which the hydroxyl group (-OH) is replaced by an alcohol residue (- OR)

Esters of carboxylic acids - compounds with a general formula.

R–COOR", where R and R" are hydrocarbon radicals.

Esters of saturated monobasic carboxylic acids have the general formula:

Physical properties:

· Volatile, colorless liquids

Poorly soluble in water

More often with a pleasant smell

Lighter than water

Esters are found in flowers, fruits, berries. They determine their specific smell.
They are an integral part of essential oils (about 3000 ef.m. are known - orange, lavender, rose, etc.)

Esters of lower carboxylic acids and lower monohydric alcohols have a pleasant smell of flowers, berries and fruits. Esters of higher monobasic acids and higher monohydric alcohols are the basis of natural waxes. For example, beeswax contains an ester of palmitic acid and myricyl alcohol (myricyl palmitate):

CH 3 (CH 2) 14 –CO–O–(CH 2) 29 CH 3

Aroma. Structural formula.	Ester name
Apple	Ethyl ether 2-methylbutanoic acid
Cherry	Formic acid amyl ester
Pear	Acetic acid isoamyl ester
A pineapple	Butyric acid ethyl ester (ethyl butyrate)
Banana	Acetic acid isobutyl ester (Isoamyl acetate also smells like a banana)
Jasmine	Acetic benzyl ether (benzylacetate)

Short names of esters are built on the name of the radical (R ") in the alcohol residue and the name of the RCOO group - in the acid residue. For example, ethyl ester of acetic acid CH 3 COO C 2 H 5 called ethyl acetate.

Application

· As fragrances and odor intensifiers in the food and perfumery (manufacturing of soap, perfumes, creams) industries;

· In the production of plastics, rubber as plasticizers.

plasticizers – substances that are introduced into the composition of polymeric materials to impart (or increase) elasticity and (or) plasticity during processing and operation.

Application in medicine

In the late 19th and early 20th centuries, when organic synthesis was taking its first steps, many esters were synthesized and tested by pharmacologists. They became the basis of such drugs as salol, validol, etc. As a local irritant and analgesic, methyl salicylate was widely used, which has now been practically superseded by more effective drugs.

Obtaining esters

Esters can be obtained by reacting carboxylic acids with alcohols ( esterification reaction). The catalysts are mineral acids.

The esterification reaction under acid catalysis is reversible. The reverse process - the splitting of an ester by the action of water to form a carboxylic acid and an alcohol - is called ester hydrolysis.

RCOOR " + H 2 O ( H +) ↔ RCOOH + R "OH

Hydrolysis in the presence of alkali proceeds irreversibly (because the resulting negatively charged carboxylate anion RCOO does not react with the nucleophilic reagent - alcohol).

This reaction is called saponification of esters(by analogy with the alkaline hydrolysis of ester bonds in fats in the production of soap).

Fats, their structure, properties and applications

"Chemistry everywhere, chemistry in everything:

In everything we breathe

In everything we drink

Everything we eat."

In everything we wear

People have long learned to isolate fat from natural objects and use it in everyday life. Fat burned in primitive lamps, illuminating the caves of primitive people, grease was smeared on skids, along which ships were launched. Fats are the main source of our nutrition. But malnutrition, a sedentary lifestyle leads to overweight. Desert animals store fat as a source of energy and water. The thick fat layer of seals and whales helps them swim in the cold waters of the Arctic Ocean.

Fats are widely distributed in nature. Along with carbohydrates and proteins, they are part of all animal and plant organisms and form one of the main parts of our food. Sources of fats are living organisms. Among the animals are cows, pigs, sheep, chickens, seals, whales, geese, fish (sharks, codfish, herring). From the liver of cod and shark, fish oil is obtained - a medicine, from herring - fats used to feed farm animals. Vegetable fats are most often liquid, they are called oils. Fats of plants such as cotton, flax, soybeans, peanuts, sesame, rapeseed, sunflower, mustard, corn, poppy, hemp, coconut, sea buckthorn, dogrose, oil palm and many others are used.

Fats perform various functions: building, energy (1 g of fat gives 9 kcal of energy), protective, storage. Fats provide 50% of the energy required by a person, so a person needs to consume 70-80 g of fat per day. Fats make up 10–20% of a healthy person's body weight. Fats are an essential source of fatty acids. Some fats contain vitamins A, D, E, K, hormones.

Many animals and humans use fat as a heat-insulating shell, for example, in some marine animals, the thickness of the fat layer reaches a meter. In addition, in the body, fats are solvents for flavors and dyes. Many vitamins, such as vitamin A, are soluble only in fats.

Some animals (more often waterfowl) use fats to lubricate their own muscle fibers.

Fats increase the effect of food satiety, as they are digested very slowly and delay the onset of hunger .

The history of the discovery of fats

Back in the 17th century. German scientist, one of the first analytical chemists Otto Tachenius(1652-1699) first suggested that fats contain a "hidden acid".

In 1741 a French chemist Claude Joseph Geoffrey(1685-1752) discovered that when soap (which was prepared by boiling fat with alkali) was decomposed with acid, a mass was formed that was greasy to the touch.

The fact that glycerin is included in the composition of fats and oils was first discovered in 1779 by the famous Swedish chemist Carl Wilhelm Scheele.

For the first time, the chemical composition of fats was determined at the beginning of the last century by a French chemist Michel Eugene Chevreul, the founder of the chemistry of fats, the author of numerous studies of their nature, summarized in a six-volume monograph "Chemical studies of bodies of animal origin".

1813 E. Chevreul established the structure of fats, thanks to the reaction of hydrolysis of fats in an alkaline medium. He showed that fats consist of glycerol and fatty acids, and this is not just a mixture of them, but a compound that, by adding water, decomposes into glycerol and acids.

Synthesis of fats

In 1854, the French chemist Marcelin Berthelot (1827–1907) carried out an esterification reaction, that is, the formation of an ester between glycerol and fatty acids, and thus synthesized fat for the first time.

General formula of fats (triglycerides)

Fats - esters of glycerol and higher carboxylic acids. The common name for these compounds is triglycerides.

Fat classification

Animal fats contain mainly glycerides of saturated acids and are solids. Vegetable fats, often referred to as oils, contain glycerides of unsaturated carboxylic acids. These are, for example, liquid sunflower, hemp and linseed oils.

Natural fats contain the following fatty acids

Saturated: stearic (C 17 H 35 COOH) palmitic (C 15 H 31 COOH) Oily (C 3 H 7 COOH)	COMPOSED ANIMALS FAT
Unsaturated : oleic (C 17 H 33 COOH, 1 double bond) linoleic (C 17 H 31 COOH, 2 double bonds) linolenic (C 17 H 29 COOH, 3 double bonds) arachidonic (C 19 H 31 COOH, 4 double bonds, less common)	COMPOSED vegetal FAT

Fats are found in all plants and animals. They are mixtures of full esters of glycerol and do not have a distinct melting point.

· Animal fats(mutton, pork, beef, etc.), as a rule, are solids with a low melting point (fish oil is an exception). Residues predominate in solid fats rich acids.

· Vegetable fats - oils (sunflower, soybean, cottonseed, etc.) - liquids (exception - coconut oil, cocoa bean oil). Oils contain mostly residues unsaturated (unsaturated) acids.

Chemical properties of fats

1. Hydrolysis, or saponification , fat occurs under the action of water, with the participation of enzymes or acid catalysts (reversibly), in this case, an alcohol is formed - glycerol and a mixture of carboxylic acids:

or alkalis (irreversible). Alkaline hydrolysis produces salts of higher fatty acids called soaps. Soaps are obtained by hydrolysis of fats in the presence of alkalis:

Soaps are potassium and sodium salts of higher carboxylic acids.

2. Hydrogenation of fats – the conversion of liquid vegetable oils into solid fats is of great importance for food purposes. The product of the hydrogenation of oils is solid fat (artificial lard, salomas). Margarine- edible fat, consists of a mixture of hydrogenated oils (sunflower, corn, cottonseed, etc.), animal fats, milk and flavorings (salt, sugar, vitamins, etc.).

This is how margarine is obtained in industry:

Under the conditions of the oil hydrogenation process (high temperature, metal catalyst), some of the acidic residues containing C=C cis bonds are isomerized into more stable trans isomers. The increased content of trans-unsaturated acid residues in margarine (especially in cheap varieties) increases the risk of atherosclerosis, cardiovascular and other diseases.

The reaction for obtaining fats (esterification)

The use of fats

Fats are food. The biological role of fats

Animal fats and vegetable oils, along with proteins and carbohydrates, are one of the main components of normal human nutrition. They are the main source of energy: 1 g of fat when fully oxidized (it takes place in cells with the participation of oxygen) provides 9.5 kcal (about 40 kJ) of energy, which is almost twice as much as can be obtained from proteins or carbohydrates. In addition, fat reserves in the body practically do not contain water, while protein and carbohydrate molecules are always surrounded by water molecules. As a result, one gram of fat provides almost 6 times more energy than one gram of animal starch - glycogen. Thus, fat should rightly be considered a high-calorie "fuel". Basically, it is spent to maintain the normal temperature of the human body, as well as to work various muscles, so even when a person does nothing (for example, sleeps), he needs about 350 kJ of energy every hour to cover energy costs, about the same power has an electric 100 - watt bulb.

To provide the body with energy in adverse conditions, fat reserves are created in it, which are deposited in the subcutaneous tissue, in the fatty fold of the peritoneum - the so-called omentum. Subcutaneous fat protects the body from hypothermia (especially this function of fat is important for marine animals). For thousands of years, people have been doing hard physical work, which required a lot of energy and, accordingly, enhanced nutrition. Only 50 g of fat is enough to cover the minimum daily human need for energy. However, with moderate physical activity, an adult should receive slightly more fat from food, but their amount should not exceed 100 g (this gives a third of the calorie content of a diet of about 3000 kcal). It should be noted that half of these 100 g is found in food in the form of so-called hidden fat. Fats are found in almost all foods: in small quantities they are even in potatoes (there are 0.4%), in bread (1–2%), and in oatmeal (6%). Milk usually contains 2-3% fat (but there are also special varieties of skimmed milk). Quite a lot of hidden fat in lean meat - from 2 to 33%. Hidden fat is present in the product in the form of individual tiny particles. Fats in almost pure form are lard and vegetable oil; in butter about 80% fat, in ghee - 98%. Of course, all the above recommendations for fat consumption are averages, they depend on gender and age, physical activity and climatic conditions. With excessive consumption of fats, a person quickly gains weight, but we should not forget that fats in the body can also be synthesized from other products. It is not so easy to “work off” extra calories through physical activity. For example, jogging 7 km, a person spends about the same amount of energy as he receives by eating just one hundred-gram bar of chocolate (35% fat, 55% carbohydrates). Physiologists have found that with physical activity, which is 10 times higher than usual, a person who received a fat diet was completely exhausted after 1.5 hours. With a carbohydrate diet, a person withstood the same load for 4 hours. This seemingly paradoxical result is explained by the peculiarities of biochemical processes. Despite the high "energy intensity" of fats, obtaining energy from them in the body is a slow process. This is due to the low reactivity of fats, especially their hydrocarbon chains. Carbohydrates, although they provide less energy than fats, "allocate" it much faster. Therefore, before physical activity, it is preferable to eat sweet rather than fatty foods. An excess of fats in food, especially animal fats, also increases the risk of developing diseases such as atherosclerosis, heart failure, etc. There is a lot of cholesterol in animal fats (but we should not forget that two-thirds of cholesterol is synthesized in the body from non-fat foods - carbohydrates and proteins).

It is known that a significant proportion of the fat consumed should be vegetable oils, which contain compounds that are very important for the body - polyunsaturated fatty acids with several double bonds. These acids are called "essential". Like vitamins, they must be supplied to the body in finished form. Of these, arachidonic acid has the highest activity (it is synthesized in the body from linoleic acid), the least activity is linolenic acid (10 times lower than linoleic acid). According to various estimates, the daily human need for linoleic acid ranges from 4 to 10 g. Most of all linoleic acid (up to 84%) is in safflower oil, squeezed from safflower seeds, an annual plant with bright orange flowers. A lot of this acid is also found in sunflower and nut oils.

According to nutritionists, a balanced diet should contain 10% polyunsaturated acids, 60% monounsaturated (mainly oleic acid) and 30% saturated. It is this ratio that is ensured if a person receives a third of the fats in the form of liquid vegetable oils - in the amount of 30–35 g per day. These oils are also found in margarine, which contains 15 to 22% saturated fatty acids, 27 to 49% unsaturated fatty acids, and 30 to 54% polyunsaturated fatty acids. By comparison, butter contains 45–50% saturated fatty acids, 22–27% unsaturated fatty acids, and less than 1% polyunsaturated fatty acids. In this respect, high-quality margarine is healthier than butter.

Must be remembered!!!

Saturated fatty acids negatively affect fat metabolism, liver function and contribute to the development of atherosclerosis. Unsaturated (especially linoleic and arachidonic acids) regulate fat metabolism and are involved in the removal of cholesterol from the body. The higher the content of unsaturated fatty acids, the lower the melting point of the fat. The calorie content of solid animal and liquid vegetable fats is approximately the same, but the physiological value of vegetable fats is much higher. Milk fat has more valuable qualities. It contains one third of unsaturated fatty acids and, remaining in the form of an emulsion, is easily absorbed by the body. Despite these positive qualities, only milk fat should not be consumed, since no fat contains an ideal composition of fatty acids. It is best to consume fats of both animal and vegetable origin. Their ratio should be 1:2.3 (70% animal and 30% vegetable) for young people and middle-aged people. The diet of older people should be dominated by vegetable fats.

Fats not only participate in metabolic processes, but are also stored in reserve (mainly in the abdominal wall and around the kidneys). Fat reserves provide metabolic processes, keeping proteins for life. This fat provides energy during physical exertion, if there is little fat in the diet, as well as in severe illness, when due to reduced appetite, it is not enough supplied with food.

Abundant consumption of fat with food is harmful to health: it is stored in large quantities in reserve, which increases body weight, sometimes leading to disfigurement of the figure. Its concentration in the blood increases, which, as a risk factor, contributes to the development of atherosclerosis, coronary heart disease, hypertension, etc.

EXERCISES

1. There is 148 g of a mixture of two organic compounds of the same composition C 3 H 6 O 2. Determine the structure of these values ​​and their mass fractions in the mixture, if it is known that one of them, when interacting with an excess of sodium bicarbonate, releases 22.4 l (N.O.) of carbon monoxide ( IV), and the other does not react with sodium carbonate and an ammonia solution of silver oxide, but when heated with an aqueous solution of sodium hydroxide, forms an alcohol and an acid salt.

Solution:

It is known that carbon monoxide ( IV ) is released when sodium carbonate reacts with acid. There can be only one acid of composition C 3 H 6 O 2 - propionic, CH 3 CH 2 COOH.

C 2 H 5 COOH + N aHCO 3 → C 2 H 5 COONa + CO 2 + H 2 O.

According to the condition, 22.4 liters of CO 2 were released, which is 1 mol, which means there were also 1 mol of acid in the mixture. The molar mass of the starting organic compounds is: M (C 3 H 6 O 2) \u003d 74 g / mol, therefore 148 g is 2 mol.

The second compound upon hydrolysis forms an alcohol and an acid salt, which means it is an ester:

RCOOR' + NaOH → RCOONa + R'OH.

The composition of C 3 H 6 O 2 corresponds to two esters: ethyl formate HSOOS 2 H 5 and methyl acetate CH 3 SOOSH 3. Esters of formic acid react with an ammonia solution of silver oxide, so the first ester does not satisfy the condition of the problem. Therefore, the second substance in the mixture is methyl acetate.

Since the mixture contained one mole of compounds with the same molar mass, their mass fractions are equal and amount to 50%.

Answer. 50% CH 3 CH 2 COOH, 50% CH 3 COOCH 3 .

2. The relative vapor density of the ester with respect to hydrogen is 44. During the hydrolysis of this ester, two compounds are formed, the combustion of equal amounts of which produces the same volumes of carbon dioxide (under the same conditions). Give the structural formula of this ether.

Solution:

The general formula of esters formed by saturated alcohols and acids is C n H 2 n About 2 . The value of n can be determined from the hydrogen density:

M (C n H 2 n O 2) \u003d 14 n + 32 = 44 . 2 = 88 g/mol,

whence n = 4, that is, the ether contains 4 carbon atoms. Since the combustion of alcohol and the acid formed during the hydrolysis of the ester releases equal volumes of carbon dioxide, the acid and alcohol contain the same number of carbon atoms, two each. Thus, the desired ester is formed by acetic acid and ethanol and is called ethyl acetate:

CH 3 -		O-S 2 H 5

Answer. Ethyl acetate, CH 3 COOS 2 H 5 .

________________________________________________________________

3. During the hydrolysis of an ester, the molar mass of which is 130 g / mol, acid A and alcohol B are formed. Determine the structure of the ester if it is known that the silver salt of the acid contains 59.66% silver by weight. Alcohol B is not oxidized by sodium dichromate and easily reacts with hydrochloric acid to form alkyl chloride.

Solution:

An ester has the general formula RCOOR ‘. It is known that the silver salt of the acid, RCOOAg , contains 59.66% silver, therefore the molar mass of salt is: M (RCOOAg) \u003d M (A g )/0.5966 = 181 g/mol, whence M (R ) \u003d 181- (12 + 2. 16 + 108) \u003d 29 g / mol. This radical is ethyl, C 2 H 5 , and the ester was formed by propionic acid: C 2 H 5 COOR '.

The molar mass of the second radical is: M (R ') \u003d M (C 2 H 5 COOR ') - M (C 2 H 5 COO) \u003d 130-73 \u003d 57 g / mol. This radical has the molecular formula C 4 H 9 . By condition, alcohol C 4 H 9 OH is not oxidized Na 2 C r 2 About 7 and easy to react with HCl therefore, this alcohol is tertiary, (CH 3) 3 SON.

Thus, the desired ester is formed by propionic acid and tert-butanol and is called tert-butyl propionate:

		CH 3
C 2 H 5 —	C-O-	C-CH3
		CH 3

Answer . tert-butyl propionate.

________________________________________________________________

4. Write two possible formulas for a fat that has 57 carbon atoms in a molecule and reacts with iodine in a ratio of 1:2. The composition of fat contains residues of acids with an even number of carbon atoms.

Solution:

General formula for fats:

where R, R', R "- hydrocarbon radicals containing an odd number of carbon atoms (another atom from the acid residue is part of the -CO- group). Three hydrocarbon radicals account for 57-6 = 51 carbon atoms. It can be assumed that each of the radicals contains 17 carbon atoms.

Since one fat molecule can attach two iodine molecules, there are two double bonds or one triple bond for three radicals. If two double bonds are in the same radical, then the fat contains a residue of linoleic acid ( R \u003d C 17 H 31) and two stearic acid residues ( R' = R "= C 17 H 35). If two double bonds are in different radicals, then the fat contains two oleic acid residues ( R \u003d R ' \u003d C 17 H 33 ) and a stearic acid residue ( R "= C 17 H 35). Possible fat formulas:

CH 2 - O - CO - C 17 H 31 CH - O - CO - C 17 H 35 CH 2 - O - CO - C 17 H 35

CH 2 - O - CO - C 17 H 33 CH - O - CO - C 17 H 35 CH - O - CO - C 17 H 33

________________________________________________________________

5.

________________________________________________________________

TASKS FOR INDEPENDENT SOLUTION

1. What is an esterification reaction.

2. What is the difference in the structure of solid and liquid fats.

3. What are the chemical properties of fats.

4. Give the reaction equation for the production of methyl formate.

5. Write the structural formulas of two esters and an acid having the composition C 3 H 6 O 2 . Name these substances according to the international nomenclature.

6. Write the equations for esterification reactions between: a) acetic acid and 3-methylbutanol-1; b) butyric acid and propanol-1. Name the ethers.

7. How many grams of fat was taken if it took 13.44 liters of hydrogen (n.o.) to hydrogenate the acid formed as a result of its hydrolysis.

8. Calculate the mass fraction of the yield of the ester formed when 32 g of acetic acid and 50 g of propanol-2 are heated in the presence of concentrated sulfuric acid, if 24 g of the ester is formed.

9. For the hydrolysis of a fat sample weighing 221 g, it took 150 g of sodium hydroxide solution with a mass fraction of alkali of 0.2. Suggest the structural formula of the original fat.

10. Calculate the volume of a potassium hydroxide solution with an alkali mass fraction of 0.25 and a density of 1.23 g / cm 3, which must be spent to carry out the hydrolysis of 15 g of a mixture consisting of ethyl ester of ethanoic acid, propyl ester of methanoic acid and methyl ester of propanoic acid.

VIDEO EXPERIENCE

1. What reaction underlies the preparation of esters:
a) neutralization	b) polymerization
c) esterification	d) hydrogenation
2. How many isomeric esters correspond to the formula C 4 H 8 O 2:
a) 2

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 formic acid methyl ester; - ethyl acetate, or ethyl ester of acetic acid.

Ways to get.

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 smell. Only esters with the smallest number of carbon atoms are soluble in water. Esters are readily soluble in alcohol and distyl ether.

Chemical properties.

1. Hydrolysis of esters is the most important reaction of this group of substances. Hydrolysis under the action of water is a reversible reaction. Alkalis are used to shift the equilibrium to the right:

2. The 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 formula for fats:

where R - radicals of higher fatty acids.

The most common fats are saturated palmitic and stearic acids and unsaturated oleic and linoleic acids.

Getting fat.

Currently, only obtaining fats from natural sources of animal or vegetable origin is of practical importance.

physical properties.

Fats formed by saturated acids are solids, and unsaturated fats are liquid. All are very poorly soluble in water, 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 salts of higher fatty acids 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 turn into residues of saturated acids, and fats from liquids turn into solids.

Of the most important nutrients - proteins, fats and carbohydrates - fats have the largest energy reserve.

Esters- functional derivatives of carboxylic acids,
in the molecules of which the hydroxyl group (-OH) is replaced by an alcohol residue (-OR)

Esters of carboxylic acids – compounds with the general formula

R–COOR",where R and R" are hydrocarbon radicals.

Esters of saturated monobasic carboxylic acids have the general formula:

Physical properties:

Volatile, colorless liquids

Poorly soluble in water

More often with a pleasant smell

Lighter than water

Esters are found in flowers, fruits, berries. They determine their specific smell.
They are an integral part of essential oils (about 3000 ef.m. are known - orange, lavender, rose, etc.)

Esters of lower carboxylic acids and lower monohydric alcohols have a pleasant smell of flowers, berries and fruits. Esters of higher monobasic acids and higher monohydric alcohols are the basis of natural waxes. For example, beeswax contains an ester of palmitic acid and myricyl alcohol (myricyl palmitate):

CH 3 (CH 2) 14 –CO–O–(CH 2) 29 CH 3

Aroma. Structural formula.	Ester name
Apple	Ethyl ether 2-methylbutanoic acid
Cherry	Formic acid amyl ester
Pear	Acetic acid isoamyl ester
A pineapple	Butyric acid ethyl ester (ethyl butyrate)
Banana	Acetic acid isobutyl ester (at isoamyl acetate also smells like a banana)
Jasmine	Acetic benzyl ether (benzyl acetate)

Short names of esters are built on the name of the radical (R ") in the alcohol residue and the name of the RCOO group - in the acid residue. For example, ethyl ester of acetic acid CH 3 COO C 2 H 5 called ethyl acetate.

Application

· As fragrances and odor intensifiers in the food and perfumery (manufacturing of soap, perfumes, creams) industries;

· In the production of plastics, rubber as plasticizers.

Plasticizers - substances that are introduced into the composition of polymeric materials to impart (or increase) elasticity and (or) plasticity during processing and operation.

Application in medicine

At the end of the 19th - beginning of the 20th century, when organic synthesis was taking its first steps, many esters were synthesized and tested by pharmacologists. They became the basis of such drugs as salol, validol, etc. As a local irritant and analgesic, methyl salicylate was widely used, which has now been practically superseded by more effective drugs.

Obtaining esters

Esters can be obtained by reacting carboxylic acids with alcohols ( esterification reaction). The catalysts are mineral acids.

Video "Obtaining acetic ethyl ether"

Video "Obtaining boron ethyl ether"

The esterification reaction under acid catalysis is reversible. The reverse process - the splitting of an ester by the action of water to form a carboxylic acid and an alcohol - is called ester hydrolysis.

RCOOR" + H2O (H+)↔ RCOOH + R"OH

Hydrolysis in the presence of alkali proceeds irreversibly (because the resulting negatively charged carboxylate anion RCOO does not react with the nucleophilic reagent - alcohol).

This reaction is called saponification of esters(by analogy with the alkaline hydrolysis of ester bonds in fats in the production of soap).

The most important representatives of esters are fats.

Fats, oils

Fats- these are esters of glycerol and higher monoatomic. The common name for such compounds is triglycerides or triacylglycerols, where acyl is a carboxylic acid residue -C(O)R. The composition of natural triglycerides includes residues of saturated acids (palmitic C 15 H 31 COOH, stearic C 17 H 35 COOH) and unsaturated acids (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH). Higher carboxylic acids, which are part of fats, always have an even number of carbon atoms (C 8 - C 18) and an unbranched hydrocarbon residue. Natural fats and oils are mixtures of glycerides of higher carboxylic acids.

The composition and structure of fats can be reflected by the general formula:

Esterification- the reaction of the formation of esters.

The composition of fats can include residues of both saturated and unsaturated carboxylic acids in various combinations.

Under normal conditions, fats containing residues of unsaturated acids in their composition are most often liquid. They are called oils. Basically, these are fats of vegetable origin - linseed, hemp, sunflower and other oils (with the exception of palm and coconut oils - solid under normal conditions). Less common are liquid fats of animal origin, such as fish oil. Most natural fats of animal origin under normal conditions are solid (fusible) substances and contain mainly residues of saturated carboxylic acids, such as mutton fat.
The composition of fats determines their physical and chemical properties.

Physical properties of fats

Fats are insoluble in water, do not have a clear melting point, and expand significantly when melted.

The aggregate state of fats is solid, this is due to the fact that fats contain residues of saturated acids and fat molecules are capable of dense packing. The composition of oils includes residues of unsaturated acids in cis - configuration, therefore, dense packing of molecules is impossible, and the state of aggregation is liquid.

Chemical properties of fats

Fats (oils) are esters and are characterized by ester reactions.

It is clear that for fats containing residues of unsaturated carboxylic acids, all reactions of unsaturated compounds are characteristic. They decolorize bromine water, enter into other addition reactions. The most important reaction in practical terms is the hydrogenation of fats. Solid esters are obtained by hydrogenation of liquid fats. It is this reaction that underlies the production of margarine, a solid fat from vegetable oils. Conventionally, this process can be described by the reaction equation:

All fats, like other esters, undergo hydrolysis:

Hydrolysis of esters is a reversible reaction. In order to form hydrolysis products, it is carried out in an alkaline environment (in the presence of alkalis or Na 2 CO 3). Under these conditions, the hydrolysis of fats proceeds reversibly, and leads to the formation of salts of carboxylic acids, which are called. fats in an alkaline environment are called saponification of fats.

When fats are saponified, glycerol and soaps are formed - sodium and potassium salts of higher carboxylic acids:

Saponification- alkaline hydrolysis of fats, obtaining soap.

Soaps- mixtures of sodium (potassium) salts of higher limiting carboxylic acids (sodium soap - solid, potassium - liquid).

Soaps are surfactants (abbreviated as surfactants, detergents). The detergent effect of soaps is due to the fact that soaps emulsify fats. Soaps form micelles with pollutants (conditionally, these are fats with various inclusions).

The lipophilic part of the soap molecule dissolves in the pollutant, while the hydrophilic part is on the surface of the micelle. Micelles are charged with the same name, therefore they repel each other, while the pollutant and water turn into an emulsion (practically, this is dirty water).

Soap also occurs in water, which creates an alkaline environment.

Soaps cannot be used in hard and sea water, as the resulting calcium (magnesium) stearates are insoluble in water.

If the initial acid is polybasic, then the formation of either full esters is possible - all HO groups are replaced, or acid esters - partial substitution. For monobasic acids, only full esters are possible (Fig. 1).

Rice. one. EXAMPLES OF ESTERS based on inorganic and carboxylic acids

Esters nomenclature.

The name is created as follows: first, the R group attached to the acid is indicated, then the name of the acid with the suffix "at" (as in the names of inorganic salts: carbon at sodium, nitr at chromium). Examples in fig. 2

Rice. 2. NAMES OF ESTERS. Fragments of molecules and their corresponding fragments of names are highlighted in the same color. Esters are usually thought of as reaction products between an acid and an alcohol, for example, butyl propionate can be thought of as the reaction product of propionic acid and butanol.

If one uses the trivial ( cm. TRIVIAL NAMES OF SUBSTANCES) the name of the starting acid, then the word “ether” is included in the name of the compound, for example, C 3 H 7 COOC 5 H 11 is the amyl ester of butyric acid.

Classification and composition of esters.

Among the studied and widely used esters, the majority are compounds derived from carboxylic acids. Esters based on mineral (inorganic) acids are not so diverse, because the class of mineral acids is less numerous than carboxylic acids (the variety of compounds is one of the hallmarks of organic chemistry).

When the number of C atoms in the initial carboxylic acid and alcohol does not exceed 6–8, the corresponding esters are colorless oily liquids, most often with a fruity odor. They form a group of fruit esters. If an aromatic alcohol (containing an aromatic nucleus) is involved in the formation of an ester, then such compounds, as a rule, have a floral rather than a fruity odor. All compounds of this group are practically insoluble in water, but readily soluble in most organic solvents. These compounds are interesting for their wide range of pleasant aromas (Table 1), some of them were first isolated from plants and later synthesized artificially.

Tab. one. SOME ESTERS, with a fruity or floral aroma (fragments of the starting alcohols in the formula of the compound and in the name are in bold type)
Ester Formula	Name	Aroma
CH 3 SOO C 4 H 9	Butyl acetate	pear
C 3 H 7 COO CH 3	Methyl butyric acid ester	apple
C 3 H 7 COO C 2 H 5	Ethyl butyric acid ester	pineapple
C 4 H 9 COO C 2 H 5	Ethyl	crimson
C 4 H 9 COO C 5 H 11	Isoamil isovaleric acid ester	banana
CH 3 SOO CH 2 C 6 H 5	Benzyl acetate	jasmine
C 6 H 5 SOO CH 2 C 6 H 5	Benzyl benzoate	floral

With an increase in the size of the organic groups that make up the esters, up to C 15–30, the compounds acquire the consistency of plastic, easily softened substances. This group is called waxes and is generally odorless. Beeswax contains a mixture of various esters, one of the components of the wax, which was able to isolate and determine its composition, is myricyl ester of palmitic acid C 15 H 31 COOC 31 H 63 . Chinese wax (a product of the isolation of cochineal - insects of East Asia) contains ceryl ester of cerotinic acid C 25 H 51 COOS 26 H 53. In addition, waxes contain both free carboxylic acids and alcohols, including large organic groups. Waxes are not wetted by water, soluble in gasoline, chloroform, benzene.

The third group is fats. Unlike the previous two groups based on ROH monohydric alcohols, all fats are esters formed from the trihydric alcohol glycerol HOCH 2 -CH (OH) -CH 2 OH. Carboxylic acids, which are part of fats, as a rule, have a hydrocarbon chain with 9-19 carbon atoms. Animal fats (cow butter, lamb, lard) are plastic, fusible substances. Vegetable fats (olive, cottonseed, sunflower oil) are viscous liquids. Animal fats mainly consist of a mixture of stearic and palmitic acid glycerides (Fig. 3A, B). Vegetable oils contain glycerides of acids with a slightly shorter carbon chain: lauric C 11 H 23 COOH and myristic C 13 H 27 COOH. (like stearic and palmitic are saturated acids). Such oils can be stored in air for a long time without changing their consistency, and therefore are called non-drying. In contrast, linseed oil contains unsaturated linoleic acid glyceride (Fig. 3B). When applied in a thin layer to the surface, such an oil dries out under the action of atmospheric oxygen during the polymerization of double bonds, and an elastic film is formed that is insoluble in water and organic solvents. On the basis of linseed oil, natural drying oil is made.

Rice. 3. GLYCERIDES OF STEARIC AND PALMITIC ACID (A AND B)- components of animal fat. Linoleic acid glyceride (B) is a component of linseed oil.

Esters of mineral acids (alkyl sulfates, alkyl borates containing fragments of lower alcohols C 1–8) are oily liquids, esters of higher alcohols (starting with C 9) are solid compounds.

Chemical properties of esters.

The most typical for esters of carboxylic acids is the hydrolytic (under the action of water) cleavage of the ester bond; in a neutral medium, it proceeds slowly and noticeably accelerates in the presence of acids or bases, because H+ and HO– ions catalyze this process (Fig. 4A), with hydroxide ions acting more efficiently. Hydrolysis in the presence of alkalis is called saponification. If we take an amount of alkali sufficient to neutralize all the acid formed, then complete saponification of the ester occurs. Such a process is carried out on an industrial scale, and glycerol and higher carboxylic acids (С15–19) are obtained in the form of alkali metal salts, which are soaps (Fig. 4B). The fragments of unsaturated acids contained in vegetable oils, like any unsaturated compounds, can be hydrogenated, hydrogen is added to double bonds, and compounds similar to animal fats are formed (Fig. 4B). In this way, solid fats are obtained in industry based on sunflower, soybean or corn oil. Margarine is made from vegetable oil hydrogenation products mixed with natural animal fats and various food additives.

The main method of synthesis is the interaction of a carboxylic acid and an alcohol, catalyzed by an acid and accompanied by the release of water. This reaction is the opposite of that shown in Fig. 3A. In order for the process to go in the right direction (ester synthesis), water is distilled (distilled off) from the reaction mixture. Special studies using labeled atoms made it possible to establish that during the synthesis, the O atom, which is part of the resulting water, is detached from the acid (marked with a red dotted frame), and not from alcohol (an unrealized variant is highlighted with a blue dotted frame).

Esters of inorganic acids, for example, nitroglycerin, are obtained according to the same scheme (Fig. 5B). Instead of acids, acid chlorides can be used; the method is applicable to both carboxylic (Fig. 5C) and inorganic acids (Fig. 5D).

The interaction of salts of carboxylic acids with haloalkyls RCl also leads to esters (Fig. 5D), the reaction is convenient because it is irreversible - the released inorganic salt is immediately removed from the organic reaction medium in the form of a precipitate.

The use of esters.

Ethyl formate HCOOS 2 H 5 and ethyl acetate H 3 COOS 2 H 5 are used as solvents for cellulose varnishes (based on nitrocellulose and cellulose acetate).

Esters based on lower alcohols and acids (Table 1) are used in the food industry to create fruit essences, and esters based on aromatic alcohols are used in the perfume industry.

Polishes, lubricants, impregnating compositions for paper (waxed paper) and leather are made from waxes, they are also part of cosmetic creams and medicinal ointments.

Fats, together with carbohydrates and proteins, make up a set of food products necessary for nutrition, they are part of all plant and animal cells, in addition, accumulating in the body, they play the role of an energy reserve. Due to the low thermal conductivity, the fat layer well protects animals (especially marine ones - whales or walruses) from hypothermia.

Animal and vegetable fats are raw materials for the production of higher carboxylic acids, detergents, and glycerin (Fig. 4), which is used in the cosmetics industry and as a component of various lubricants.

Nitroglycerin (Fig. 4) is a well-known drug and explosive, the basis of dynamite.

On the basis of vegetable oils, drying oils are made (Fig. 3), which form the basis of oil paints.

Sulfuric acid esters (Fig. 2) are used in organic synthesis as alkylating agents (introducing an alkyl group into the compound), and phosphoric acid esters (Fig. 5) are used as insecticides, as well as additives to lubricating oils.

Mikhail Levitsky