Thermal decomposition of diazodiphenylmethane catalysed by sulphur compounds in the presence of oxygen

Abstract

Thermal decomposition at 80 °C of diazodiphenylmethane in oxygen-saturated chlorobenzene in the presence of sulphur compounds (5)–(8) affords tetraphenylethylene, benzophenone, benzophenone azine, as well as small amounts of bisdiphenylmethyl ether. Kinetic and product studies indicate that chain decomposition of the diazoalkane takes place in the presence of sulphides (5)–(8), in competition with unimolecular decomposition leading to diphenylcarbene. Evidence has been obtained that the extent of the chain reaction increases linearly with increasing the concentration of added sulphide and is somewhat dependent on the nature of the sulphur compounds (5)–(8), which appear to exert only a catalytic effect. Addition of n-butanol to chlorobenzene leads to increase in the rate of the chain process at low alcohol concentrations (0.1–0.5M) with formation of large amounts of diphenylmethyl n-butyl ether and suppression of tetraphenylethylene, but no occurrence of the chain decomposition reaction is observed at alcohol concentrations > ca. 5.0M. Results are rationalized in terms of reaction of the initially formed diphenylcarbene with oxygen and sulphides (5)–(8), affording some species capable of acting as initiator of the chain decomposition of the diazoalkane, in which the chain carrier might be the diazoalkane radical cation, Ph₂CN₂⁺˙