In the absence of organic solvent and phase-transfer reagent, the catalytic oxidation of cyclohexene to adipic acid with aqueous 30% hydrogen peroxide can be achieved in the presence of tungstic acid/acidic organic additive. When the molar ratio of tungstic acid∶acidic organic additive∶cyclohexene∶hydrogen peroxide was 1∶1∶40∶176 (tungstic acid, 2.5 mmol) and the tungstic acid/resorcinol used as catalyst, the isolated yield of adipic acid was up to 90.9% for 8 h. If the tungstic acid alone was used as catalyst, the isolated yield of adipic acid was only 72.1% and the purity of product was low. With sulfosalicylic acid, oxalic acid or salicylic acid used as additives, the isolated yield of adipic acid increased with increasing reaction time, but after 6 h, it did not increase obviously. The yield and purity of adipic acid were very high when the amount of sulfosalicylic acid was 2.5 mmol in the reaction medium. Tungstic acid/sulfosalicylic acid catalyst can be reused five times and the isolated yield of adipic acid was still 80.5% in the fifth time.

Key words: cyclohexene, tungstic acid, adipic acid, hydrogen peroxide, catalytic oxidation