Esters: general characteristics and application

Esters - products of replacement of hydrogen atoms of the hydroxyl group of carboxylic acids and mineral carbon radical.Distinguish mono-, di-, and polyesters.For monobasic acids exist mono, di- and polybasic acids - total and acid esters.The name consists of the title ester acid and alcohol involved in its formation.For the names of esters often use a trivial or historical range.According to the IUPAC name of esters formed as follows: take the name of a radical alcohol, add the name of both hydrocarbon and acid end -oat.For example, esters of structural formulas (isomers and metamers) corresponding to the molecular formula S4N802, according to various nomenclatures referred to as: propilformiat (propilmetanoat) izopropilformiat (izopripilmetanoat), ethyl acetate (etiletanoat) melpropionat (methylpropanoate).

Getting esters .These compounds are widely distributed in nature.For example, esters of low molecular weight and secondary carboxylic acids of the homologous series are part of the essential oils of many plants (eg uksusnoizoamilovy ether, or "pear essence," which is part of the pears and many colors), and esters of glycerol and higher fatty acids - the chemical basis of all fatand oils.Some esters are prepared synthetically.

esterification reaction takes place by the interaction of carboxylic (and mineral) acids with alcohols.As the catalyst is very strong mineral acid (often used H2S04).The catalyst activates the carboxylic acid molecule.

esterification reaction rate also depends on the carbon atom with which is associated an OH group (primary, secondary or tertiary), the chemical nature of the acid and alcohol, as well as the structure of the hydrocarbon chain, which is linked with the carboxyl.

ester hydrolysis .The hydrolysis reaction (saponification) esters - esterification reaction is the reverse.It takes it slow.If added to the reaction mixture, the mixture of mineral acids or alkalis, its velocity increases.Saponification alkalies occurs a thousand times faster than the acid.The esters are hydrolyzed in an alkaline medium, and ethers - in acidic.When heated

esters with alcohols in the presence of acid sulphate or alcoholates (alkaline medium) alkoxy exchange occurs.This forms a new ester, and the reaction medium is returned alcohol, which previously was in the form of residues in the ester molecule.

Esters : the reduction reaction.Reducing most often aluminum hydride, lithium, sodium in boiling alcohol.Esters of high resistance to the action of different oxidants used in chemical synthesis or analysis to protect alcoholic and phenolic groups.

Esters: main representatives.Ethyl ethanoate (acetate ester) was obtained by the esterification reaction of ethanol and acetate acid catalyst (acid sulphate).Ethyl ethanoate is used as a solvent of cellulose nitrate in the production of smokeless gunpowder, and photographic film, fruit essences component for the food industry.

Izoamiletanoat (uksusnoizoamilovy ether, "pear essence") is highly soluble in ethanol, ethyl ether.Acetate acid obtained by esterification of isoamyl alcohol.Izoamilmetilbutanoat used as a flavor component in perfumery and as a solvent.

Izoamilizovaleriat ("apple" essence, izovalerianovoizoamilovy ether) is prepared by esterification of isovaleric acid and isoamyl alcohol.Said ester is used as a fruit essences in the food industry.