Preparation.
1. Esterification. Esters are most easily prepared by the interaction of acids and alcohols in presence of conc. H2SO4. Thus
\(C_3COOH +HOC_2H_5 \xrightarrow [or\,dry\,HCl\,gas]{conc.\,H_2SO_4} \underset {Ethyl\,acetate}{CH_3COOC_2H_5}\)
2. By the action of acetyl chloride or acetic anhydride on ethanol.
3. By the action of ethyl halide on silver acetate.
\(\underset {Silver\,acetate}{CH_3COOAg}+BrC_2H_5 \longrightarrow CH_3COOC_2H_5+AgBr\)
4. Methyl esters can be prepared by the action of diazomethane on carboxylic acids.
RCOOH + CH2N2 → RCOOCH3 + N2
5. By the condensation of acetaldehyde in presence of aluminium ethoxide (Tischenko reaction).
\(2CH_3CH \xrightarrow [Tischeno\,reaction]{Al(OC_2H_5)_3} CH_3COOC_2H_5\)
Properties.
It is a colourless sweet smelling liquid. There is no intermolecular hydrogen bonding in esters, hence their m.p. and b.p. are low as compared to those of the corresponding carboxylic acids.
1. Hydrolysis in presence of acid. It is a reversible reaction.
\(\underset {Ethyl\,acetate}{CH_3COOC_2H_5}+H_2O \,\,\overset{H^ +}{\rightleftharpoons} \,\, \underset {Acetic\,Acid}{CH_3COOH}+ \underset {Ethanol}{C_2H_5OH}\)
2. Hydrolysis in presence of base (saponification). It is an irreversible reaction.
Since alkali (sod. or pot.) salts of higher fatty acids (stearic, palmitic, etc.) are soaps, alkaline hydrolysis of esters is often called saponification.
3. Ammonolysis (splitting by ammonia).
\(CH_3COOC_2H_5 +NH_3 \longrightarrow \underset {Acetamide}{CH_3CONH_2}+C_2H_5OH\)
4. Reduction may be done by means of sodium and alcohol (Bouveault Blanc reduction), lithium aluminium hydride or by hydrogen gas in presence of copper chromite as catalyst at 200-300°C under pressure.
\(CH_3COOC_2H_5 +4[H]\,or\, 2H_2 \longrightarrow \underset {Ethanol\,(2\,moles)}{CH_3CH_2OH +C_2H_5OH}\)
5. Reaction with phosphorus pentachloride.
\(CH_3COOC_2H_5 +PCl_5 \longrightarrow \underset {Acetyl\,chloride}{CH_3COCl}+ \underset {Ethyl,chloride}{C_2H_5Cl+POCl_3}\)
6. Claisen condensation.
Claisen condensation may be defined as the condensation of a molecule of ester with a molecule of aldehyde, ketone or ester in the presence of sodium ethoxide (C2H5OH + Na) to give B-keto ester provided at least one of the constituents has at least one a-hydrogen atom.
\(\underset {Ethyl\,acetate\,(2,moles)}{CH_3COOC_2H_5+HCH_2COOC_2H_5}\,\, \xrightarrow[(-C_2H_5OH)]{C_2H_5ONa}\)
\(\underset {Acetoacetic\,ester\,(Ethyl\,acetoacetate)}{CH_3COCH_2COOC_2H_5}\)
7. Reaction with Grignard reagent forms acetone or t-butyl alcohol depending upon the amount of the Grignard reagent.
Recall that esters of formic acid give secondary alcohols on treatment with excess of Grignard reagents.
Uses. Ethyl acetate is used
(i) in the preparation of artificial perfumes and essences.
(ii) as a solvent for oils, fats, gums, varnishes, etc.
(iii) for the treatment of skin diseases.
