Ethers features of the structure. Esters: chemical properties and applications. Classification and composition of esters

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

where R and R" are hydrocarbon radicals (in the complex esters of formic acid, R is a hydrogen atom).

Nomenclature and isomerism. The names of esters are derived from the name of the hydrocarbon radical and the name of the acid, in which the suffix -am is used instead of the ending -ova, for example:

Esters are characterized by three types of isomerism:

1. The isomerism of the carbon chain begins at the acid residue with butanoic acid, at the alcohol residue - with propyl alcohol, for example, ethyl butyrate is isomeric with ethyl isobutyrate, propyl acetate and isopropyl acetate.
2. Isomerism of the position of the ester group --CO--O--. This type of isomerism begins with esters containing at least 4 carbon atoms, such as ethyl acetate and methyl propionate.
3. Interclass isomerism, for example propanoic acid is isomeric to methyl acetate.

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. Esters of lower carboxylic acids and alcohols are volatile, water-insoluble liquids. Many of them have a pleasant smell. So, for example, butyl butyrate smells like pineapple, isoamyl acetate smells like pear, etc.

Esters of higher fatty acids and alcohols - waxy substances, odorless, insoluble in water.

Chemical properties of esters. 1. The reaction of hydrolysis, or saponification. Since the esterification reaction is reversible, therefore, in the presence of acids, the reverse hydrolysis reaction proceeds:

The hydrolysis reaction is also catalyzed by alkalis; in this case, hydrolysis is irreversible, since the resulting acid with alkali forms a salt:

2. Addition reaction. Esters containing an unsaturated acid or alcohol in their composition are capable of addition reactions.
3. Recovery reaction. The reduction of esters with hydrogen leads to the formation of two alcohols:

4. The reaction of the formation of amides. Under the action of ammonia, esters are converted into acid amides and alcohols:

17. Structure, classification, isomerism, nomenclature, production methods, physical properties, Chemical properties amino acids

Amino acids (aminocarbomic acids) -- organic compounds, the molecule of which simultaneously contains carboxyl and amine groups.

Amino acids can be considered as derivatives of carboxylic acids in which one or more hydrogen atoms are replaced by amine groups.

Amino acids - colorless crystalline substances, highly soluble in water. Many of them have a sweet taste. All amino acids are amphoteric compounds, they can exhibit both acid properties, due to the presence in their molecules of the carboxyl group --COOH, and the main properties due to the amino group --NH2. Amino acids interact with acids and alkalis:

NH2 --CH2 --COOH + HCl > HCl * NH2 --CH2 --COOH (glycine hydrochloride salt)

NH 2 --CH 2 --COOH + NaOH > H 2 O + NH 2 --CH 2 --COONa (glycine sodium salt)

Due to this, solutions of amino acids in water have the properties of buffer solutions, i.e. are in a state of internal salts.

NH 2 --CH 2 COOH N + H 3 --CH 2 COO -

Amino acids can usually enter into all reactions characteristic of carboxylic acids and amines.

Esterification:

NH 2 --CH 2 --COOH + CH 3 OH > H 2 O + NH 2 --CH 2 --COOCH 3 (glycine methyl ester)

An important feature of amino acids is their ability to polycondensate, leading to the formation of polyamides, including peptides, proteins, nylon, and capron.

Peptide formation reaction:

HOOC --CH2 --NH --H + HOOC --CH2 --NH2 > HOOC --CH2 --NH --CO --CH2 --NH2 + H2O

The isoelectric point of an amino acid is the pH value at which the maximum proportion of amino acid molecules has a zero charge. At this pH, the amino acid is the least mobile in an electric field, and this property can be used to separate amino acids as well as proteins and peptides.

A zwitterion is an amino acid molecule in which the amino group is represented as -NH 3 +, and the carboxy group is represented as -COO? . Such a molecule has a significant dipole moment at zero net charge. It is from such molecules that the crystals of most amino acids are built.

Some amino acids have multiple amino groups and carboxyl groups. For these amino acids, it is difficult to speak of any particular zwitterion.

Most amino acids can be obtained during the hydrolysis of proteins or as a result of chemical reactions:

CH 3 COOH + Cl 2 + (catalyst) > CH 2 ClCOOH + HCl; CH 2 ClCOOH + 2NH 3 > NH 2 --CH 2 COOH + NH 4 Cl

March 5, 2018

Esters are usually called compounds obtained by the reaction of esterification from carboxylic acids. In this case, the OH- is replaced from the carboxyl group by the alkoxy radical. As a result, esters are formed, the formula of which is in general view written as R-COO-R".

The structure of the ester group

Polarity chemical bonds in ester molecules is similar to the polarity of bonds in carboxylic acids. The main difference is the absence of a mobile hydrogen atom, in place of which a hydrocarbon residue is placed. However, the electrophilic center is located on the carbon atom of the ester group. But the carbon atom of the alkyl group connected to it is also positively polarized.

Electrophilicity, and hence the chemical properties of esters, are determined by the structure of the hydrocarbon residue that has taken the place of the H atom in the carboxyl group. If the hydrocarbon radical forms a conjugated system with the oxygen atom, then the reactivity increases markedly. This happens, for example, in acrylic and vinyl esters.

Physical Properties

Most esters are liquid or crystalline substances with a pleasant aroma. Their boiling point is usually lower than those of similar values. molecular weights carboxylic acids. This confirms the decrease in intermolecular interactions, and this, in turn, is explained by the absence of hydrogen bonds between neighboring molecules.

However, just like the chemical properties of esters, the physical ones depend on the structural features of the molecule. More precisely, on the type of alcohol and carboxylic acid from which it is formed. On this basis, esters are divided into three main groups:

Fruit esters. They are formed from lower carboxylic acids and the same monohydric alcohols. Liquids with characteristic pleasant floral-fruity odors.
Waxes. They are derivatives of higher (number of carbon atoms from 15 to 30) acids and alcohols having one functional group each. These are plastic substances that soften easily in the hands. The main component of beeswax is myricyl palmitate C 15 H 31 COOS 31 H 63, and Chinese - ceryl ester of cerotinic acid C 25 H 51 COOS 26 H 53. They are insoluble in water, but soluble in chloroform and benzene.
Fats. Formed from glycerol and medium and higher carboxylic acids. Animal fats, as a rule, are solid under normal conditions, but melt easily when the temperature rises (butter, lard, etc.). Vegetable fats are characterized by a liquid state (linseed, olive, soybean oils). The fundamental difference in the structure of these two groups, which affects the differences in the physical and chemical properties of esters, is the presence or absence of multiple bonds in the acid residue. Animal fats are glycerides of unsaturated carboxylic acids, and vegetable fats are saturated acids.

Chemical properties

Esters react with nucleophiles, resulting in substitution of the alkoxy group and acylation (or alkylation) of the nucleophilic agent. If there is an α-hydrogen atom in the structural formula of the ester, then ester condensation is possible.

1. Hydrolysis. Acid and alkaline hydrolysis is possible, which is the reverse reaction of esterification. In the first case, the hydrolysis is reversible, and the acid acts as a catalyst:

R-COO-R "+ H 2 O<―>R-COO-H + R "-OH

Basic hydrolysis is irreversible and is usually called saponification, and sodium and potassium salts of fatty carboxylic acids are called soaps:

R-COO-R" + NaOH ―> R-COO-Na + R"-OH

2. Ammonolysis. Ammonia can act as a nucleophilic agent:

R-COO-R "+ NH 3 ―> R-CO-NH 2 + R"-OH

3. Interesterification. This chemical property of esters can also be attributed to the methods of their preparation. Under the action of alcohols in the presence of H + or OH - it is possible to replace the hydrocarbon radical combined with oxygen:

R-COO-R" + R""-OH ―> R-COO-R"" + R"-OH

4. Reduction with hydrogen leads to the formation of molecules of two different alcohols:

R-СО-OR "+ LiAlH 4 ―> R-СΗ 2 -ОH + R"OH

5. Combustion is another typical reaction for esters:

2CΗ 3 -COO-CΗ 3 + 7O 2 \u003d 6CO 2 + 6H 2 O

6. Hydrogenation. If there are multiple bonds in the hydrocarbon chain of an ether molecule, then hydrogen molecules can be attached to them, which occurs in the presence of platinum or other catalysts. So, for example, it is possible to obtain solid hydrogenated fats (margarine) from oils.

The use of esters

Esters and their derivatives are used in various industries. Many of them dissolve various organic compounds well, are used in perfumery and food industry, for the production of polymers and polyester fibers.

Ethyl acetate. It is used as a solvent for nitrocellulose, cellulose acetate and other polymers, for the manufacture and dissolution of varnishes. Due to its pleasant aroma, it is used in the food and perfume industries.

Butyl acetate. Also used as a solvent, but already polyester resins.

Vinyl acetate (CH 3 -COO-CH=CH 2). It is used as the basis of a polymer necessary in the preparation of adhesives, varnishes, synthetic fibers and films.

Malonic ether. Due to its special chemical properties, this ester is widely used in chemical synthesis to obtain carboxylic acids, heterocyclic compounds, aminocarboxylic acids.

Phthalates. Esters of phthalic acid are used as plasticizers for polymers and synthetic rubbers, and dioctyl phthalate is also used as a repellent.

Methyl acrylate and methyl methacrylate. Easily polymerized with the formation of organic glass sheets resistant to various influences.

Derivatives of carboxylic or inorganic acids, in which the hydrogen atom in the hydroxyl group is replaced by a radical, are called esters. Usually the general formula of esters is denoted as two hydrocarbon radicals attached to a carboxyl group - C n H 2n + 1 -COO-C n H 2n + 1 or R-COOR '.

Nomenclature

The names of esters are made up of the names of the radical and acid with the suffix "-at". For example:

CH3COOH- methyl formate;
HCOOCH 3- ethyl formate;
CH 3 COOC 4 H 9- butyl acetate;
CH 3 -CH 2 -COO-C 4 H 9- butylpropionate;
CH 3 -SO 4 -CH 3- dimethyl sulfate.

The trivial names of the acid that is part of the compound are also used:

S 3 H 7 COOS 5 H 11- amyl ester of butyric acid;
HCOOCH 3- methyl ester of formic acid;
CH 3 -COO-CH 2 -CH (CH 3) 2- isobutyl ester of acetic acid.

Rice. 1. Structural formulas of esters with names.

Classification

Esters are divided into two groups depending on their origin:

esters of carboxylic acids- contain hydrocarbon radicals;
esters of inorganic acids- include the rest of mineral salts (C 2 H 5 OSO 2 OH, (CH 3 O)P(O)(OH) 2 , C 2 H 5 ONO).

The most diverse esters of carboxylic acids. Their physical properties depend on the complexity of the structure. Esters of lower carboxylic acids - volatile liquids with a pleasant aroma, higher - solids. These are poorly soluble compounds floating on the surface of the water.

Types of esters of carboxylic acids are shown in the table.

*View*	*Description*	*Examples*
fruit esters	Liquids whose molecules contain no more than eight carbon atoms. They have a fruity aroma. Composed of monohydric alcohols and carboxylic acids	CH 3 -COO-CH 2 -CH 2 -CH (CH 3) 2- isoamyl ester of acetic acid (smell of pear); C 3 H 7 -COO-C 2 H 5- ethyl ester of butyric acid (smell of pineapple); CH 3 -COO-CH 2 -CH- (CH 3) 2- isobutyl ester of acetic acid (banana smell).
	Liquid (oils) and solids containing from nine to 19 carbon atoms. Composed of glycerol and residues of carboxylic (fatty) acids	Olive oil - a mixture of glycerin with residues of palmitic, stearic, oleic, linoleic acids
	Solids with 15-45 carbon atoms	CH 3 (CH 2) 14 -CO-O- (CH 2) 29 CH 3-myricyl palmitate

Rice. 2. Wax.

Esters of carboxylic acids are the main component of aromatic essential oils found in fruits, flowers, and berries. Also included in beeswax.

Rice. 3. Essential oils.

Receipt

Esters are obtained in several ways:

esterification reaction of carboxylic acids with alcohols:
CH 3 COOH + C 2 H 5 OH → CH 3 COOC 2 H 5 + H 2 O;
reaction of carboxylic acid anhydrides with alcohols:
(CH 3 CO) 2 O + 2C 2 H 5 OH → 2CH 3 COOC 2 H 5 + H 2 O;
the reaction of salts of carboxylic acids with halocarbons:
CH 3 (CH 2) 10 COONa + CH 3 Cl → CH 3 (CH 2) 10 COOCH 3 + NaCl;
addition reaction of carboxylic acids to alkenes:
CH 3 COOH + CH 2 \u003d CH 2 → CH 3 COOCH 2 CH 3 + H 2 O.

Properties

The chemical properties of esters are due to the -COOH functional group. The main properties of esters are described in the table.

Esters are used in cosmetology, medicine, food industry as flavors, solvents, fillers.

What have we learned?

From the topic of the 10th grade chemistry lesson, we learned what esters are. These are compounds containing two radicals and a carboxyl group. Depending on the origin, they may contain residues of mineral or carboxylic acids. Esters of carboxylic acids are divided into three groups: fats, waxes, fruit esters. These are poorly soluble substances in water with a low density and a pleasant aroma. Esters react with alkalis, water, halogens, alcohols and ammonia.

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Esters are thermally unstable: when heated up to 200 - 250 o C they decompose into much more stable carboxylic acids and alkenes, For example:

If the first carbon atom of the alcohol part of the ester has a branch, then two different alkenes are obtained, and each of them can be obtained in the form of two cis- and trance- isomers:

Esters can be hydrolyzed in acidic, neutral and alkaline environments. The reaction is reversible and its rate depends on the concentration of the added strong acid. Kinetic curves, ie time-concentration curves, have a descending exponent for ester and the same ascending exponent for alcohol and carboxylic acid. Below is a graph for the hydrolysis reaction in general form:

If acid is not added, then an autocatalytic process is observed: hydrolysis at first proceeds very slowly, but at the same time carboxylic acid is formed - the catalyst and the process accelerates, and after a while its speed drops again and the concentration of the ester reaches equilibrium. This equilibrium concentration, other things being equal, does not differ in any way from the equilibrium concentration obtained by catalysis with strong acids. However, the time to reach half-life (t 1/2 ) much bigger:

Under the action of alkalis, esters are also “hydrolyzed”, but here the alkali is not a catalyst, but a reagent:

Esters enter into an interesterification reaction with both alcohols and acids:

In order to shift the equilibrium towards the formation of the target ester, alcohol - the initial reagent is taken in a large excess. When interesterification with acid is taken in a large excess of it.

The esters react with ammonia and amines. The equilibrium in these reactions is very strongly shifted towards the formation of amides and alkylamides of acids: an excess of ammonia or amine is not needed (!!!)

Esters can be oxidized with strong oxidizing agents in an acidic environment. Apparently, hydrolysis first occurs and only the alcohol formed in this case is actually oxidized. For example:

Esters can be reduced to alcohols with sodium metal in an alcohol medium. The reaction was proposed in 1903 and studied in detail in 1906 by the French chemists Bouvot and Blanc, and bears their name. For example:

In two steps, esters can be reduced to alcohols using complex metal hydrides. In the first stage, in the case of using sodium tetrahydroborate, boric acid ester and sodium alcoholate are obtained, in the second they are hydrolyzed to alcohols:

In the case of using lithium tetrahydroaluminate, aluminum and lithium alcoholates are obtained in the first stage, and in the second they are also hydrolyzed to alcohols:

Title of the topic or topic section	page no.
Complex ethers. Definition.
Esters classification
Esters nomenclature
Isomerism of esters
Interfunctional ester isomers
Electronic and spatial structure of esters on the example of methyl acetate
Methods for obtaining esters
Obtaining esters by the interaction of carboxylic acids with alkenes.
Obtaining esters by the interaction of carboxylic acids with alkynes.
Obtaining esters by the interaction of alkynes, carbon monoxide and alcohols.
Obtaining esters by the interaction of carboxylic acids and alcohols is an esterification reaction.
Obtaining esters by interaction of chlorine (halogen) anhydrides of carboxylic acids and alcohols.
Obtaining esters by the interaction of acid halides with alcoholates.
Obtaining esters by the interaction of anhydrides of carboxylic acids and alcohols.
Obtaining esters by the interaction of anhydrides of carboxylic acids with alcoholates
Obtaining esters by the interaction of anhydrides and halides of carboxylic acids with phenols.
Obtaining esters by the interaction of anhydrides and halides of carboxylic acids with phenolates (naphtholates).
Obtaining esters by the interaction of salts of carboxylic acids and halide alkyls
Preparation of esters from other esters by acid transesterification reactions
Obtaining esters from other esters by reactions of interesterification with alcohol.
Obtaining esters from ethers by reacting them with carbon monoxide
Physical properties, applications and biomedical significance of esters
Physical properties of esters
The ratio of esters to light
Aggregate state of esters
The dependence of the melting and boiling points of esters on the number of carbon atoms in them and on the structure. Table No. 1
The dependence of the boiling points of esters on the structure of the radical of their alcohol part. Table number 2
Solubility and Solubility of Esters
Solubility of esters in water, ethanol and diethyl ether at 20 o C. Table No. 3
Solubility of esters in relation to varnishes and paints, as well as to inorganic salts
The smell of esters.
The smell of esters, their use, natural occurrence and toxic properties. Table No. 4
Medico-biological significance of esters
Formulas of esters - medicinal biologically active drugs
Chemical properties of esters
Thermal decomposition of esters into carboxylic acids and alkenes
Hydrolysis of esters in an acidic medium. Kinetic curves.
Hydrolysis of esters in water. Kinetic curves of autocatalysis.
The reaction of esters with alkalis. Kinetic curves.
Transesterification reaction of esters with alcohols and acids.
The reaction of esters with ammonia and amines is the production of acid amides.
Oxidation reaction of esters with strong oxidizing agents in an acidic medium.
Recovery reaction of esters to alcohols according to Bouvot and Blanc
The reaction of the reduction of esters to alcohols using complex metal hydrides
Content

The structure of the ester group

The polarity of chemical bonds in ester molecules is similar to the polarity of bonds in carboxylic acids. The main difference is the absence of a mobile hydrogen atom, in place of which a hydrocarbon residue is placed. However, the electrophilic center is located on the carbon atom of the ester group. But the carbon atom of the alkyl group connected to it is also positively polarized.

Physical Properties

Most esters are liquid or crystalline substances with a pleasant aroma. Their boiling point is usually lower than that of similar molecular weight carboxylic acids. This confirms the decrease in intermolecular interactions, and this, in turn, is explained by the absence of hydrogen bonds between neighboring molecules.

Fruit esters. They are formed from lower carboxylic acids and the same monohydric alcohols. Liquids with characteristic pleasant floral-fruity odors.
Waxes. They are derivatives of higher (number of carbon atoms from 15 to 30) acids and alcohols having one functional group each. These are plastic substances that soften easily in the hands. The main component of beeswax is myricyl palmitate C 15 H 31 COOS 31 H 63, and Chinese - ceryl ester of cerotinic acid C 25 H 51 COOS 26 H 53. They are insoluble in water, but soluble in chloroform and benzene.
Fats. Formed from glycerol and medium and higher carboxylic acids. Animal fats, as a rule, are solid under normal conditions, but melt easily when the temperature rises (butter, lard, etc.). Vegetable fats are characterized by a liquid state (linseed, olive, soybean oils). The fundamental difference in the structure of these two groups, which affects the differences in the physical and chemical properties of esters, is the presence or absence of multiple bonds in the acid residue. Animal fats are glycerides of unsaturated carboxylic acids, and vegetable fats are saturated acids.

Chemical properties

1. Hydrolysis. Acid and alkaline hydrolysis is possible, which is the reverse reaction of esterification. In the first case, the hydrolysis is reversible, and the acid acts as a catalyst:

R-COO-R "+ H 2 O<―>R-COO-H + R "-OH

Basic hydrolysis is irreversible and is usually called saponification, and sodium and potassium salts of fatty carboxylic acids are called soaps:

R-COO-R" + NaOH ―> R-COO-Na + R"-OH

2. Ammonolysis. Ammonia can act as a nucleophilic agent:

R-COO-R "+ NH 3 ―> R-CO-NH 2 + R"-OH

R-COO-R" + R""-OH ―> R-COO-R"" + R"-OH

4. Reduction with hydrogen leads to the formation of molecules of two different alcohols:

R-СО-OR "+ LiAlH 4 ―> R-СΗ 2 -ОH + R"OH

5. Combustion is another typical reaction for esters:

2CΗ 3 -COO-CΗ 3 + 7O 2 \u003d 6CO 2 + 6H 2 O

The use of esters

Butyl acetate. Also used as a solvent, but already polyester resins.

Vinyl acetate (CH 3 -COO-CH=CH 2). It is used as the basis of a polymer necessary in the preparation of adhesives, varnishes, synthetic fibers and films.

Malonic ether. Due to its special chemical properties, this ester is widely used in chemical synthesis to obtain carboxylic acids, heterocyclic compounds, aminocarboxylic acids.