A proposed free radical mechanism of this microwave assisted direct oxidation is depicted in scheme
2. Upon microwave irradiation, TBHP is broken down into t-butoxide and hydroxyl radicals.
Abstraction of a hydrogen radical from toluene gives a benzyl radical that combines with a hydroxyl
radical to yield benzyl alcohol. Further oxidation could lead to benzaldehyde (or its hydrate) then
benzoic acid. In fact, if we limited the amount of TBHP to 4 equivalents, tiny amount of benzaldehyde
was detected in the 1HNMR spectra of the reaction mixture.