Continuous-flow synthesis of (E)-2-Hexenal intermediates using a two-stage microreactor system

Abstract

A flow synthesis method of (E)-2-hexenal intermediates by employing a two-stage microreactor system was reported as an example of autothermal Prins-type reaction. The continuous flow technology not only overcame the low efficiency of batch reactions, it also met the demand for high selectivity and required less consumption of reactants. Temperature monitors of a micro-mixer and a reaction tube covered by thick thermal insulation materials provided an apparent reaction enthalpy of −112 kJ·mol−1 for the generations of hexenal intermediates and by-products. A two-stage reaction platform was therefore developed to enable efficient control of the reaction temperature, which was from 20 °C and 110 °C. Under optimized operating conditions, the yield of (E)-2-hexenal intermediates reached 72%, with a space time yield of 273 kg·h−1 L−1, which was over 1200 times that of a traditional batch reactor with dripping fed reactants. The final yield of (E)-2-hexenal was maintained at 72% after hydrolysis of the intermediates.