Esters are the products of substitution of hydrogen atoms of the hydroxyl group of carboxylic and mineral acids by a carbon radical. There are mono-, di- and polyesters. For monobasic acids there are monoesters, dibasic and polybasic acids - full and acid esters. The name of the ester consists of the name of the acid and alcohol involved in its formation. For the name of ethers, trivial or historical nomenclature is often used. According to the IUPAC nomenclature, the names of the esters are formed as follows: they take the name of the alcohol in the form of a radical, add the name of the acid as a hydrocarbon and the end-oat. For example, the structural formulas of esters (isomers and metamers) corresponding to the molecular formula C4H802 are called according to different nomenclatures as follows: propyl formate (propyl methanoate), isopropyl formate (isopripyl methanoate), ethyl acetate (ethyl ethanoate), melpropionate (methyl propanoate).
Getting esters . These compounds are widespread in nature. Thus, homologous low-molecular and medium carboxylic acid esters are part of the essential oils of many plants (for example, acetic isoamyl ether, or “pear essence”, which is part of pears and many flowers), and glycerol and higher fatty acid esters are the chemical basis of all fats and oils. Some esters are synthetically prepared.
The esterification reaction occurs as a result of the interaction of carboxylic (and mineral) acids with alcohols. A strong mineral acid acts as a catalyst (H2S04 is most often used). The catalyst activates the carboxylic acid molecule .
The rate of the esterification reaction also depends on which carbon atom the OH group is associated with (primary, secondary or tertiary), on the chemical nature of the acid and alcohol, and also on the structure of the hydrocarbon chain that is associated with the carboxyl.
Hydrolysis of esters . The hydrolysis (saponification) of esters is a reverse esterification reaction. She walks slowly. If a mixture of mineral acids or alkalis is added to the reaction mixture, its speed increases. Saponification with alkalis occurs a thousand times faster than acids. Esters are hydrolyzed in an alkaline environment, and ethers in an acidic environment.
When esters with alcohols are heated in the presence of sulfate acid or alcoholates (in an alkaline environment), alkoxy groups are exchanged. In this case, a new ether is formed, and alcohol, which used to be a part of the ether molecule as residues, returns to the reaction medium.
Esters : reduction reaction. Reducers are most often aluminum hydrates of lithium, sodium in boiling alcohol. The high resistance of esters to the action of various oxidizing agents is used in chemical synthesis or analysis to protect alcohol and phenolic groups.
Esters: main representatives. Ethyl ethanoate (ethyl acetate) is obtained through the esterification of acetate acid and ethanol ( sulfate acid catalyst ). Ethyl ethanoate is used as a solvent for cellulose nitrate in the production of smokeless powder, photo and film films, and a component of fruit essences for the food industry.
Isoamylethanoate (acetic isoamyl ether, “pear essence”) is readily soluble in ethanol, diethyl ether. Obtained by esterification of acetate acid and isoamyl alcohol. Isoamylmethylbutanoate is used as an aromatic component in perfumes and as a solvent.
Isoamyl valerate ("apple" essence, isovalerianovoyloisoamyl ether) is obtained by the esterification of isovalerianic acid and isoamyl alcohol. The specified ether is used as a fruit essence in the food industry.