Esters are a class of compounds widely distributed in nature. The simple ester tend to have pleasant odors.
In many cases although not exclusively so the characteristic flavors and fragrances of flowers and fruits are due to compounds with the ester functional group. An exception is the case of the essential oils.
Esters hydrolyzed by boiling water slowly to carboxylic acids and phenols. The hydrolysis is accelerated in the presence of mineral acid on alkali.
The formation of esters is known as esterification.
The esterification of carboxylic acids with alcohols is a kind of nucleophilic acyl substitution. The first step is the protonation of the carbonyl oxygen, which activates the carbonyl group towards nucleophilic addition of the alcohol.
The above mechanism is supported by the using isotopically labeled methanol (CH3O18H) with acetic acid to give methyl acetate (having labeled oxygen) and water not containing any isotopic oxygen.
Esters of phenols are prepared by reversible acylation of phenols with acyl chloride or anhydrides rather than the reaction with carboxylic acid in which all the steps are reversible.→ Read More
Esters react with alcohols in the presence of an acid catalyst to undergo exchange of alcohol resides i.e., alkoxy parts. The equilibrium mixture consists of the reactants and a new ester and a new alcohol. The reaction involves nucleophilic acyl substitution of the alkoxy group of the ester with the alkoxy group of the alcohol and is known as trans esterification.
Esters react with ammonia and amines to form amides
The acyl group of the ester is reduced with LiAlH4 (but not with NaBH4) to a primary alcohol.
Catalytic hydrogenation of esters to alcohols is not easy unlike that of aldehydes and ketones. The reaction requires high temperature and pressure. The catalyst used is a mixture of oxides known as copper chromite. The alkoxy part of the ester gives the corresponding alcohol as by product.
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