Direct and Sensitized Photolyses of O- (p-Anisoyl)-N, N-dibenzylhydroxylamineSubstituent, Deuterium Isotope and Heavy Atom Effects on the lmine-Forming Radical Elimination

Abstract

The direct photolysis of O-(p-anisoy1)-N, N-dibenzylhydroxylamine (1a) in polar and nonpolar solvents was found to give N-benzylidenebenzylamine (2a) and P-anisic acid (3a) in a 1: 1 stoichiometry without leading to anisole (4a). The results of triplet-quenching experiments show that the photolysis proceeds preferentially through the excited singlet tate. An analysis of substituent and deuterium isotope effects on the quantum yields for the reaction of la provides strong evidence that 4a is derived from decarboxylation of the anisoyloxyl radical escaped from the triplet cage but not from the singlet, and that in the latter cage hydrogen abstraction forming the elimination products 2a and 3a and recombina tion affording the starting 1a occur exclusively. On the other hand, intersystem crossing of the triplet anisoyloxyl-dibenzylaminyl radical pair intermediate was demonstrated to inherently take place in a high efficiency, based on a kinetic consideration of internal heavy-atom effects on the triplet -sensitized photolysis of 1a in acetonitrile.