Reactions of substituted 1,3-diphenyltriazenes with phenyl isocyanates. Catalysis and substituent effects

Abstract

Reactions of phenyl isocyanate with 12 monosubstituted and 15 symmetrical disubstituted 1,3-diphenyltriazanes have been studied in tetrahydrofurane at 25°C. The found rate constants correlate with the Hammett substituent constants, the slopes being - 1.206 and - 1.682 in case of the monosubstituted and the disubstituted compounds, respectively. Under conditions of pseudomonomolecular reaction catalysis by the products and that by the catalysts used in reactions of isocyanates with amines or hydroxy compounds have not been observed. Rates of reactions of 6 substituted phenyl isocyanates with the parent 1,3-diphenyltriazane have also been measured. In this case the found rate constants correlate with the Hammett substituent constants, the slope being +1.038. The results indicate that the reaction involves rate limiting formation of a six-membered cyclic complex which successively undergoes only a rapid reorganization of electrons.