Aroyl peroxides. Part 7. The effects of additives on the thermolysis of aroyl peroxides in arenes and the elimination of possible complications in the measurement of partial rate factors for phenylation

Abstract

Competitive homolytic arylation of arenes has been carried out under conditions in which biaryl formation is maximised. Improved yields of biaryl were obtained with o-chloroanil, nitro- and nitroso-compounds, and transition metal salts; nitrosobenzene, pentafluoronitrosobenzene, copper(II) benzoate, and iron(III) benzoate caused nearly theoretical yields of biaryl and aroic acid. Partial rate factors, measured under such conditions, are free from uncertainties arising from the selective removal of σ-complexes by side-processes such as dimerisation. The possibility that arenes form complexes with aryl radicals or their precursors as a necessary part of the selection process between substrate molecules was not confirmed in studies of the application of the additivity principle and of the multiplication rule, and of variation in the relative concentration of the two competing arenes. The absence of any discrepancies indicates that the measured partial rate factors are not influenced by such putative complex formation. The mechanism of action of these catalysts has been investigated.