Studies of the Cage Effect of Solvent. I. Photolysis of Azomethane in n-Hexane

Abstract

Abstract Azomethane in n-hexane solution has been decomposed by irradiation of 366 mμ over the temperature range −75 to 80°C, in order to study the effect of the solvent cage on the photolysis. The main products have been found to be nitrogen, methane and ethane. The yield of methane increases, but that of ethane, which amounts to 88% of nitrogen at −75°C, decreases with the rise in temperature. The addition of styrene as a scavenger for methyl radicals in an increasing amount suppresses the formation of methane almost completely, while that of ethane is not affected, indicating that ethane is exclusively formed by the cage combination of an azomethane molecule. The formation of methane is explained by the abstraction of the hydrogen atom from a solvent molecule by methyl radicals that have escaped the original cage. The material balance represented as ((1/2)CH4+C2H6)/N2 is nearly 100% below room temperature, but it falls off slightly at higher temperatures; this may be ascribed to addition reactions of methyl radicals. The quantum yield of photolysis is apparently smaller than unity and falls off with a lowering of the temperature; this probably arises from the cage recombination of the initially formed pair of radicals CH3N2 and CH3, though the former radical is very short-lived.