METHYLTHIO GROUP MIGRATION IN THE ACID-CATALYZED HYDROLYSIS OF S-METHYL PHENYLDIAZOTHIOACETATE - KINETICS AND MECHANISM OF THE REACTION

The acid-catalyzed hydrolysis of S-methyl phenyldiazothioacetate, C6H5C(=N2)COSCH3, in aqueous solution at 25-degrees-C was found to occur with the hydronium ion isotope effect k(H)+/k(D)+ = 3.08 and to give a Bronsted relation, based on carboxylic acid catalysts, whose exponent is alpha = 0.70. This is taken to mean that the reaction occurs by rate-determining proton transfer to the diazo carbon atom. The principal product of the reaction, however, is alpha-(methylthio)-alpha-phenylacetic acid, C6H5CH(SCH3)-CO2H, which must be formed by 1,2-shift of the methylthio group. An argument is presented which suggests that this shift is accompanied by a rate acceleration and that it consequently must take place in the rate-determining step of the reaction.