Catalytic oxidation of o-xylene

Oxidation of o-xylene to phthalic anhydride over V2O5-TiO2 catalyst has been studied in order to detect the intermediates of this conversion. The oxidation of alcohols such as o-methylbenzyl alcohol and o-xylene-α,α′-diol yields the same compounds as those obtained from the hydrocarbon in the same conditions, whereas oxidation of o-toluic acid yields mainly the lactone, phthalide. Moreover, a competitive oxidation of inactive o-methylbenzyl alcohol, and o-xylene (methyl-14C) results in the formation of o-tolualdehyde, phthalide, and phthalic anhydride, having different specific radioactivities, and demonstrates that different reaction paths are involved. A mechanism is proposed in which the selective incorporation of oxygen occurs after abstraction of one hydrogen atom so as to produce a surface alcoholate ion, whereas degradation into maleic anhydrides and carbon oxides arises from substitution of hydrogen atoms of the aromatic nucleus by oxygen.