Kinetics and mechanism of hydrolysis of 4-phenylallophanates

Abstract

The kinetics of hydrolysis of aryl and alkyl 4-phenylallophanates to phenylurea and phenol or alchol are studied. Acid–base catalysis, deuterium solvent isotope effects, and entropy of activation provide good evidence for a changeover in mechanism from E1cB for aryl allophanates to B_Ac2 for alkyl esters. The parameters of the Hammett and Yukawa–Tsuno relationships for aryl esters and the non-linear Brönsted correlation with the pK_a values of the leaving groups are in good agreement with the proposed mechanisms.