Intermediates in the decomposition of aliphatic diazo-compounds. Part 15. Radical cations in the decomposition of diazodiphenylmethane by copper(II) perchlorate and by tris(p-bromophenyl)ammoniumyl perchlorate

Abstract

The kinetics and products of the decomposition of diazodiphenylmethane by copper(II) perchlorate and by tris-(p-bromophenyl)ammoniumyl perchlorate in acetonitrile solvent have been investigated. The similarity of the two reactions suggests that both the copper and the ammoniumyl salt act as initiators of a chain decomposition in which the chain carriers are radical cations. E.s.r. studies of reaction mixtures in other solvents, notably n-heptyl cyanide, indicate that two different radical cations are formed during the reaction; one, detectable at low temperatures, is believed to be the radical cation formed by simple removal of one electron from the diazoalkane by the initiator, and the other is shown to be the radical cation of benzophenone azine, one of the products of the reaction. In acetonitrile as solvent the major reaction product is tetraphenylethylene, but the ratio of this olefin to benzophenone azine changes from solvent to solvent and in some cases depends upon whether or not oxygen is present. The addition of water to acetonitrile leads to changes in the rate of decomposition of the diazo-compound with both initiators which indicate progressive, and at water concentrations greater than about 0.3M almost total, incursion of a perchloric acid-catalysed decomposition pathway involving rate-limiting formation of diphenylmethyl cations. This has been confirmed by measurement of the kinetic deuterium isotope effect of replacing the added water by deuterium oxide.