Preparation of p-isopropylbenzaldehyde (p-cuminal) by direct electrochemical oxidation of p-isopropyltoluene (p-cymene) in methanolic medium

The direct anodic oxidation of p-isopropyltoluene (p-cymene) in methanolic solutions gives in part the p-isopropylbenzaldehyde dimethyl acetal, which produces the p-isopropylbenzaldehyde (p-cuminal) by hydrolysis in sulfuric acid medium. Since several parallel reactions are possible, we have investigated, in an undivided cell equipped with a magnetic stirrer, the influence of the following parameters on the p-cuminal production: nature of the solvent, nature of the supporting electrolyte, nature of the anode, initial p-cymene concentration, anodic current density, amount of electricity supplied to the system and temperature. For the optimum conditions, the conversion of p-cymene was higher than 95% and the p-cuminal selectivity was 58-59%:. We have also investigated the production of p-cuminal in two electrochemical cells transposable on a large scale. The former was a reactor equipped with a cylindrical graphite anode and the latter was an electrochemical cell equipped with a how-through reticulated vitreous carbon anode. In these cases, we observed that the p-cuminal production increases with either the rate of stirring or the flow rate of the electrolyte. (C) 2001 Elsevier Science Ltd. All rights reserved.