Esters: general characteristics and application

Esters are products of the replacement of hydrogen atoms of the hydroxyl group of carboxylic and mineral acids with a carbon radical. There are mono-, di- and polyesters. For monobasic acids there are monoesters, dibasic and polybasic acids - complete and acid esters. The name of the ether consists of the name of the acid and alcohol involved in its formation. For the names of ethers, trivial or historical nomenclature is often used. According to the nomenclature of IUPAC, the names of the esters are formed as follows: take the name of alcohol as a radical, add the name of the acid as a hydrocarbon and the ending -at. For example, the structural formulas of esters (isomers and metamers), corresponding to the molecular formula C4H802, are named for different nomenclatures: propyl formate (propylmethanoate), isopropyl formate (isopropylmethanoate), ethyl acetate (ethyl etanoate), melpropionate (methyl propanoate).

Preparation of esters . These compounds are widely distributed in nature. Thus, esters of low molecular and medium carboxylic acids of the homologous series are part of the essential oils of many plants (for example, acetic isoamyl ether or "pear essence", which is part of pears and many colors), and esters of glycerol and higher fatty acids are the chemical basis of all fats And oils. Some esters are obtained synthetically.

The esterification reaction occurs as a result of the interaction of carboxylic (and mineral) acids with alcohols. The catalyst is a strong mineral acid (most often H2S04). The catalyst activates the carboxylic acid molecule .

The rate of the esterification reaction also depends on the carbon atom of the OH group (primary, secondary or tertiary), the chemical nature of the acid and alcohol, and the structure of the hydrocarbon chain that is bonded to the carboxyl.

Hydrolysis of esters . The reaction of hydrolysis (saponification) of esters is a reversible reaction of esterification. It passes slowly. If a mixture of mineral acids or alkalis is added to the reaction mixture, its rate increases. Saponification by alkalis occurs a thousand times faster than acids. Esters are hydrolyzed in alkaline medium, and ethers - in acidic.

When the esters are heated with alcohols in the presence of sulfate acid or alkoxides (in an alkaline medium), alkoxy groups are exchanged. At the same time, a new ether is formed, and alcohol is returned to the reaction medium, which previously was in the form of residues in the composition of the ether molecule.

Esters : the reaction of reduction. Reducers are most often lithium aluminum hydrides, sodium in boiling alcohol. The high resistance of esters to the action of various oxidants is used in chemical synthesis or analysis to protect alcohol and phenolic groups.

Esters: main representatives. Ethylethanoate (acetic ethyl ether) is obtained from the esterification reaction of acetate acid and ethanol ( sulfate acid catalyst ). Ethyl ethoate is used as a solvent for cellulose nitrate in the production of smokeless powder, photo and film, a component of fruit essences for the food industry.

Isoamylethanoate (acetic isoamyl ether, "pear essence") is readily soluble in ethanol, diethyl ether. It is obtained by esterification of acetate acid and isoamyl alcohol. Isoamylmethylbutanoate is used as an aromatic component in perfumery and as a solvent.

The isoamyl isovalerate ("apple" essence, isovalerian isoamyl ether) is obtained by the esterification reaction of isovaleric acid and isoamyl alcohol. This ether is used as a fruit essence in the food industry.