Abstract
Although the hydrolysis of carboxylic esters in acid or in alkaline media usually takes place by mechanism I, there has become available, during recent years, ample evidence that mechanism II does also occur, especially when the alkyl group R 11 has strong electron-releasing properties. [mathematical equation] Mechanism II, which implies the liberation of the carbonium cation, R 11, during some stage of the reaction, can be observed in the case of optically active esters by the racemisation of the products of the reaction. It has been shown that the optically pure hydrogen phthalic esters of certain substituted allyl alcohols, when submitted by hydrolysis with only a slight excess of alkali, yield the partly racemised alcohols; but when larger proportions of alkali are used optically pure alcohols are obtained (Arcus and Kenyon, J.C.S, 1938, 1912). The most complete demonstration of mechanism II has been provided in the case of optically active p-methoxybenzhydryl hydrogen phthalate the powerful electron-release of the p-methoxyl group causing the ester to dissociate with great ease (Balfe, Doughty, Kenyon and Poplett, J.C.S, 1942, 605). In the present investigation it has been shown that the following secondary alcohols and their derivatives react chiefly by mechanism II: 1. -Naphthylanisyl carbinol. 2. p-Methyl p-methoxy benzhydrol. 3. p-Isoproply-p-methoxybenzhdyrol. 4. -Naphthyl-o-methoxyphenyl carboninol. -Naphthylanisyl carbinol has been resolved into its (+) and (-) forms by the fractional crystallisation of alkalcidal salts of its hydrogen phthalic and hydrogen succinic esters. The hydrogen lysis of these optically active acid esters, when carried out under suitable experimental conditions, has been shown to proceed by alkyl-oxygen fission. This receives strong confirmation from the other reactions of the optically active carbinol and its esters, in all of which mechanism II is the usual mode of reaction. The reactions of the esters of p-methyl-p-methoxybenzhdrol, p-iso-propyl-p-methoxybenzhydrol, and a-naphthyl-o-methoxyphenyl carbonil are similar to those of the esters of ?-naphthylanisyl carbonil and alkyl-oxygen fission may also be assumed in the reactions of these compounds.