Intermediates in the decomposition of aliphatic diazo-compounds. Part XI. Mechanistic studies on the reaction of diphenylmethylene with amines in solution

Abstract

The kinetics and products of thermal decomposition of diphenyldiazomethane in acetonitrile containing n- and t-butylamines have been investigated. It is established that the principal product, N-(diphenylmethyl)butylamine is formed by reaction of the primary amine with diphenylmethylene. In the formation of the secondary amine, the absence of an intermolecular hydrogen isotope effect, determined from the ratio of yields from reactions with butylamine and NN-dideuteriobutylamine, and the substantial value of the intramolecular isotope effect, obtained from the radioactivity of the secondary amine produced from N-tritiated butylamine, are shown to be consistent with initial attack of the singlet carbene on the nitrogen atom of the amine followed by rearrangement of the resulting ylide rather than a hydrogen-abstraction–recombination mechanism. The latter mechanism for reaction of the triplet carbene has been detected by CIDNP studies, the intermediate radical pair giving rise to diphenylmethane as well as the secondary amine, but both in small amounts. The prinicpal product arising from the triplet carbene is, however, tetraphenylethane, and comparison of the inter- and intra-molecular isotope effects on its formation suggest that conversion of the singlet state of diphenylmethylene into the triplet may be irreversible under these reaction conditions.