CHEMICAL-IONIZATION MASS-SPECTROMETRY OF BENZOYL PEROXIDE - A RADICALAROMATIC-SUBSTITUTION RESULTING IN BIPHENYLCARBOXYLIC ACID IN THE GAS-PHASE

A radical aromatic substitution resulting in biphenylcarboxylic acid i s inferred for the decomposition of benzoyl peroxide from the chemical ionization and collision-induced dissociation mass spectra. The therm olysis of benzoyl peroxide gives rise to a benzoyloxy radical, which u ndergoes rapid decarboxylation and hydrogen abstraction leading to phe nyl radical and benzoic acid, respectively. Attack of the resulting ph enyl radical on the benzoic acid results in bipbenylcarboxylic acid. O n the other hand, the phenyl radical abstracts a hydrogen atom to yiel d benzene, which is then subjected to the attack of a benzoyloxy radic al, affording phenyl benzoate. This substitution reaction rather than the recombination of benzoyloxy and phenyl radicals is found to be res ponsible for the formation of phenyl benzoate under the present condit ions.