Continuous oxidation of toluene derivatives to aromatic aldehydes in an umbrella-shaped microchannel reactor

In an umbrella-shaped microchannel reactor, the continuous selective aerobic oxidation of toluene derivatives to aromatic aldehydes over a Co/Mn/Br catalytic system using acetic acid/water as the solvent was studied. Taking the oxidation of p-nitrotoluene (PNT) to p-nitrobenzaldehyde (PNBD) as a model, the effects of the Co²⁺(Mn²⁺) amount, ratio of Co²⁺, Mn²⁺ and Br⁻, reaction temperature, reaction pressure, oxygen flow rate, residence time and water content on the reaction were systematically investigated. Under the optimized reaction conditions, an 11.8% conversion could be achieved with a good selectivity of 67.1% to PNBD, significantly superior to the results obtained in a kettle reactor. In addition, various toluene derivatives could be tolerated by the present reaction process. This aerobic oxidation over the microchannel reaction technology has the features of an easy-to-operate process and easily controlled reaction parameters, providing an economical and environmentally friendly protocol for the synthesis of aromatic aldehydes.