LIQUID-PHASE OXIDATION OF p-CYMENE: NATURE OF INTERMEDIATE HYDROPEROXIDES AND RELATIVE ACTIVITY OF THE ALKYL GROUPS

A study has been made of the liquid-phase oxidation of p-cymene with elemental oxygen using emulsion and photochemical procedures with the object of determining (a) the nature of the resulting hydroperoxides and their decomposition products, and (b) the relative activity of the methyl and isopropyl side chains.The following compounds have been shown to be present in the emulsion oxidation product: 2-p-tolyl-2-propyl hydroperoxide, 2-p-tolyl-2-propanol, p-isopropylbenzyl alcohol, p-methylacetophenone, cumic acid, p-(α-hydroperoxyisopropyl) benzoic acid, p-(α-hydroxyisopropyl) benzoic acid, and p-acetyl-benzoic acid. The two hydroperoxides have been isolated and characterized. By chromatographic separation of the carboxylic acids and fractional distillation of the alcohols formed by lithium aluminum hydride reduction of all other products, the relative susceptibility of the methyl and isopropyl groups to oxidative attack has been shown to be 1:4.In the photochemical oxidation, hydroperoxide decomposition was very small and the product was shown to consist of 20% p-isopropylbenzyl hydroperoxide and 80% of 2-p-tolyl-2-propyl hydroperoxide. The relative extent of oxidative attack at the two positions was therefore identical in the two oxidations.