Synthesis of benzaldehyde by swern oxidation of benzyl alcohol in a continuous flow microreactor system

Abstract

Preparation of benzaldehyde by Swern oxidation of benzyl alcohol was carried out in a continuous flow microreactor system. Dimethyl sulfoxide (Me 2 SO) was used as oxidizing agent and oxalyl chloride or p-toluenesulfonyl (p-TsCl) chloride was used as the activating agent. Benzyl alcohol was oxidized to benzaldehyde by the Me 2 SO-activating agent mixture in the continuous flow microreactor system. The optimized reaction conditions of the Swern oxidation were as follows: oxalyl chloride was used as the activating agent; the mole ratio of Me 2 SO, oxalyl chloride, and benzyl alcohol was 4:2:1; the flow rate of Me 2 SO was 1.5 mL/min; the reaction temperature was 15 ◦ C; length of delay loop was 1.5 m; a Caterpillar Split-Recombine Micro Mixer was used; and all of the experiments were completed at atmospheric pressure. The yield of benzaldehyde can reach 84.7% with selectivity of 98.5%. Due to the small reactor volume and short residence times, the Swern oxidation of benzyl alcohol in a continuous flow microreactor system can be operated at nearly room temperature (5–19 ◦ C) instead of –70 ◦ C in a batch reaction, with residence time of reactants in microreactors in milliseconds instead of several hours in a batch reaction.