Chemical ionization mass spectrometry of benzoyl peroxide: A radical aromatic substitution resulting in biphenylcarboxylic acid in the gas phase

A radical aromatic substitution resulting in biphenylcarboxylic acid is inferred for the decomposition of benzoyl peroxide from the chemical ionization and collision‐induced dissociation mass spectra. The thermolysis of benzoyl peroxide gives rise to a benzoyloxy radical, which undergoes rapid decarboxylation and hydrogen ion leading to phenyl radical and benzoic acid, respectively. Attack of the resulting phenyl radical on the benzoic acid results in biphenylcarboxylic acid. On the other hand, the phenyl radical s a hydrogen atom to yield benzene, which is then subjected to the attack of a benzoyloxy radical, affording phenyl benzoate. This substitution reaction rather than the recombination of benzoyloxy and phenyl radicals is found to be responsible for the formation of phenyl benzoate under the present conditions.