Kinetic studies of the uncatalysed and catalysed hydrolysis of some N - carbobenzoxy amino acid p - nitrophenyl esters

Abstract

Because of the difficulties encountered by Main L.Main; 'Kinetic Studies of Amino Acid Ester Hydrolysis.' M.Sc.Thesis.Victoria Universiy of Wellington.1966 in measuring and interpreting the spontaneous hydrolysis of active amino acid esters, the uncatalysed hydrolysis of the N-protected, N-carbobenzoxy glycine and other amino acid p-nitrophenyl esters was investigated. The protection of the amino group eliminated the problem of catalysis by absorbed carbon dioxide, and enabled determination of lyate species. In addition, a study was made of the influence of (a) the α-substituent, and (b) temperature in the hydrolysis of these N-carbobenzoxy esters. The hydrolysis of N-carbobenzoxy glycine p-nitrophenyl ester is catalysed by (1) imidazole (2) o-mercaptobenzoic acid, and (3) cysteine. Each of the hydrolysis reactions displayed a first-order dependence on the catalyst concentration. pH-rate studies of the imidazole and o-mercaptobenzoic acid catalysed reactions revealed that free imidazole and the mercaptide dianion were the catalytically active species. The reactions (1) and (3) proceed via nucleophilic pathways involving the formation and decomposition of (1) an N-acylimidasole (case (1)) (2) a thioester (case (3)) as intermediate species.