The mechanism of photochemical reactions in solution. Part I. The ultraviolet photolysis of diphenylacetylene

Abstract

The ultraviolet photolysis of dilute solutions of diphenylacetylene in hexane containing dissolved oxygen has been investigated. The main product of the reaction is benzoic acid. Benzene, hexylhydroperoxide, and 2- and 3- hexyl benzoates are also formed. The reactive intermediate is thought to be the benzoyloxy-radical formed by the addition of a molecule of oxygen to a molecule of diphenylacetylene in its triplet excited state. Photoaddition of a further molecule of oxygen to this intermediate and subsequent breakdown of the resulting molecule forms two benzoyloxy-radicals. The observed products may be formed from the benzoyloxy-radicals by abstraction of hydrogen from the solvent or by elimination of carbon dioxide followed by hydrogen abstraction by the resulting phenyl radicals. The effect of photosensitisers, quenchers, and a change of solvent on the reaction have been studied.