Indirect Electrooxidation (an Ex-Cell Method) of Alkylbenzenes by Recycle Use of (NH4)2Ce(NO3)6 in Various Solvent Systems

Article abstract of DOI:10.1021/jo00348a007

Indirect electrooxidation (an ex-cell method) of the side chain of alkylbenzenes has been performed by recycle use of (NH4)2Ce(NO3)6 (CAN) in various solvent systems.The side-chain oxidation of p-methoxytoluene (1) with CAN in methanol proceeds smoothly, yielding anisaldehyde (3, 94percent), while use of aqueous methanol or acetic acid resulted in a mixture of 3 and the dimeric product 4 (19-35percent) along with complex products (28-47percent).Electrooxidation of the recovered cerium(III) salts was perfomed smoothly in methanol by passing 1.1-1.2 F/mol of electricity to give a reddish methanol solution of CAN, which can be used for the next oxidation of 1.The repeated use of CAN over 10 times produced the desired 3 in over 90percent yields.Similarly, the oxidation of alkylbenzenes, bearing p-methoxy group, gave the corresponding side-chain-oxidized products.In contrast, p-tert-butyltoluene (9e) could be oxidized by heating with CAN in aqueous 50percent acetic acid at 85-90 deg C to give p-tert-butylbenzaldehyde in over 90percent yield.The regeneration of CAN after the oxidation of 9e was also accomplished by electrolysis in the aqueous 50percent acetic acid system.The reaction mechanisms in connection with the nature of CAN in various solvent systems are discussed.