Aromatic hydroxylation. Part V. Photoinduced oxidation of some benzenoid compounds by trialkyl phosphite esters and oxygen

Abstract

The hydroxylation of aromatic compounds by use of trialkyl phosphite and oxygen is initiated either by light or the thermolysis of benzoyl peroxide. The phenolic product distribution and the relative reactivities of the substrates suggest that the hydroxylating species is an electrophilic radical. A correlation of the partial rate factors for meta- and para-substitution by the Hammett–Brown method gives a ρ value of –1·26. A mechanism is suggested in which the aromatic compound is co-oxidised with the trialkyl phosphite by a free-radical process. The rate-determining step in the hydroxylation is the addition of the radical to aromatic nucleus.