The kinetics and mechanism of aminolysis of isothiocyanates

Abstract

A study of the kinetics of aminolysis of p-nitrophenyl isothiocyanate by n-butylamine, benzylamine, dibenzylamine, p-anisidine, m-toluidine, N-methylaniline, and p-chloroaniline in diethyl ether and iso-octane as solvents has shown that many of the reactions involve kinetic terms that are second order in amine. The detailed behaviour reveals that aminolysis occurs via an intermediate of amine–isothiocyanate (1:1) stoicheiometry which undergoes subsequent prototropic rearrangement catalysed by a second amine molecule. Added carboxylic acids inhibit aminolysis by strong bases by their removal as inactive amine–acid (1 : 2) complexes, but with bases with which they form only a negligible amount of complex, acids can catalyse the aminolysis, probably by their effect on the prototropic rearrangement. Added thioureas (products) have negligible catalytic effects in the presence of an excess of amine. Our results and conclusions are similar to findings for the aminolysis of isocyanates in water.