Esterification, in absence of special catalysts

Because of its acidity any carboxylic acid must catalyse its own esterification, so that esters can be produced merely by heating together the acid and the alcohol. Indeed, strongly acidic carboxylic acids such as formic, oxalic, and pyruvic acid pass into their esters simply when heated with an alcohol and this method assumes preparative importance when the instability of the carboxylic acid in presence of mineral acids excludes the use of the latter as catalyst for the esterification. 

The yield of ester can be raised appreciably by continuous removal of the water produced. If neither of the reactants boils at a lower temperature than water, the latter can be removed merely by distillation, as in the preparation of triglycerides from glycerol and a relatively involatile higher fatty acid or in the preparation of pentyl pyruvate. According to Simon794 the latter ester is obtained in 99% yield by heating pyruvic acid and the equivalent amount of pentyl alcohol in a water-pump vacuum, provided that after equilibrium has become established the water formed is slowly distilled off. 

Benzyl phenylacetate Phenylacetic acid (1 mole) and benzyl alcohol (2 moles) are heated in a round-bottomed flask (500 ml) under a descending condenser so that a mixture of benzyl alcohol and water distils over. The upper, aqueous, layer of the distillate is removed and the benzyl alcohol is returned to the flask. After 1-1.5 days the reaction is complete, 1 mole of water having distilled off. The mixture is finally fractionated in a vacuum, yielding benzyl phenylacetate, b.p. 270°/166 mm, in a 95% yield. 

Continuous removal of the product water by azeotropic distillation after addition of a carrier such as benzene, toluene, xylene, or a halogenated aliphatic solvent leads to rapid esterification ( azeotropic esterification ) and usually also to high yields. The course of the reaction can be followed directly from the amount of water liberated the apparatus used for this purpose (a water separator) is well known. 

Thielepape795 removed the product water from the azeotropic mixture by allowing the distillate to drop into an extraction thimble filled with calcium carbide before the organic phase was returned to the reaction mixture. 

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