Reaction XCVI.—Hydrolysis of Esters to Acids

Reaction XCVI. Hydrolysis of Esters to Acids. (A., 186, 161 204, 127 215, 26 Ann. Rep., 1930, 146.)—When esters are heated with water, hydrolysis occurs, but does not go to completion, the reaction being reversible. 

however, aqueous or alcoholic caustic alkali is used, by combining with the acid as formed, it shifts the equilibrium point of the reaction, and almost complete hydrolysis occurs. This reaction could also have been dealt with under Chapter XIII, since alcohols are simultaneously formed however, the hydrolysis is more usually undertaken to obtain the acid. Other special cases of hydrolysis have been dealt with elsewhere (see Reaction LXVII.). The general method of procedure will be clear from the following. 

20 gms. (1 mol.) of ethyl acetate (see p. 256) are refluxed with 80 gms. (excess) of 25% aqueous caustic potash for 1 hour, until the layer of ester has disappeared, and the mixture no longer smells of it. The whole is then distilled to 100° ethyl alcohol can be separated from the distillate by addition of anhydrous potassium carbonate. The residue in the flask is neutralised with dilute sulphuric acid and evaporated to dryness on a water bath. The solid residue is powdered and distilled with 50 gms. of cone, sulphuric acid to 130°, and the distillate fractionated between 115° and 120°. 

Cooling in ice until solidification takes place, and subsequently draining away the still-liquid portion, gives crystals of glacial acetic acid. 

20 gms. of diethyl-ethylmalonate (see p. 137) are gradually added to 50 gms. (excess) of 50% aqueous caustic potash in a flask fitted with a reflux condenser, and cooled in water. The mixture so obtained is heated on a water bath with shaking until, after a vigorous reaction, complete liquefaction has occurred (1 hour). The liquid is cooled, diluted with an equal volume of water, acidified with cone, hydrochloric acid, and ex- 

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