RELATION BETWEEN THERMAL AND PHOTOCHEMICAL HYDROLYSES OF DIAZONIUM SALTS

In the presence of chloride ion, aryl chlorides as well as phenols result from the photolysis of arane-diazonium salts in aqueous solution, as in the thermal reaction. Benzenediazonium ion in aqueous sodium chloride yields just as much chlorobenzene in the photolysis as it does thermally at the same temperature, but others (p-CH3C6H4N2+, pCIC6H4N2+) give a significantly higher yield of the chloride photochemically than thermally. A similarity but not identity of product-determining steps is indicated. When p-CH3C6H415N+≡N and p-CH3OC6-H415N+≡N are exposed to light insufficient to complete the photolysis, the residual diazonium salt is in part rearranged to Ar+N15≡N, and the relative extents of rearrangement to hydrolysis are significantly more than in the corresponding dark hydrolysis. There are major uncertainties in the photochemical mechanism, but it can be unequivocally concluded that there is no single intermediate common to the photochemical and thermal reactions. © 1969, American Chemical Society. All rights reserved.