Jean P. Calmon

Kinetics and mechanism of hydrolysis of O-aryl N-phenylthiocarbamates

In kinetic studies of the hydrolysis ofaseries of O-aryl N-phenylthiocarbamates, evidence for the formation of phenyl isothiocyanate is a decisive argument for an E1cB mechanism. The high value of the Hammett parameter (ρ 3.0) and the positive value of the entropy of activation (ΔS‡+ 10.8 cal mol–1 K–1) are discussed as mechanistic criteria which can be used to establish the occurrence of an EIcB mechanism when the intermediate cannot be isolated.

Kinetics and mechanisms of decarboxylation of 4-phenylallophanate anions

The decarboxylation of a series of 4-phenylallophanate anions has been studied as a function of pH and buffer concentration. A changeover in mechanism is revealed from Hammett and Bronsted correlations, entropy values, and solvent isotope effects. A concerted mechanism in acid and neutral media is proposed, whereas in basic media the results may be explained by a spontaneous decomposition or by a cyclic reaction with involvement of a molecule of water.