Oxidation of dibenzyl ether with nitric acid to benzaldehyde in continuous-flow microreactors

Abstract

As an important chemical, benzaldehyde (BzH) can be synthesized by oxidizing dibenzyl ether (DBE) with nitric acid (HNO₃). This is an environmentally friendly and chlorine-free production process, but it has problems such as intense in situ gas generation, low space–time yield and safety issues. This study developed a safe and efficient continuous-flow synthesis method using a packed-bed microreactor. Five critical parameters including reaction residence time, glass bead particle size, temperature, oxidant concentration, and initiator dosage were systematically investigated. Under optimal conditions (T = 85 °C, d = 104.5 μm, HNO₃ eq. = 3 and NaNO₂ eq. = 0.009), the conversion of DBE and the yield of BzH reached 80.11% and 96.35% after 17.92 min. The space–time yield was twice that of capillary microreactors and 40 times that of batch reactors. The reasons for in situ gas production in capillary microreactors and its negative impacts were explored. A kinetic model was developed, providing significant theoretical insights and practical value for better understanding the oxidation process and optimizing the process parameters.