Preparation of Insoluble Bis(2-bromoacetyl)biphenyl via a Photoultrasound Enhanced Continuous Flow Reaction

In continuous multiphase flow photochemical reactions, the generation of insoluble materials can significantly reduce the efficiency of material and light energy transfer between interfaces due to numerous interfaces within the hybrid system. The problem of solids blocking pipelines further compounds this issue. This study presents the design and construction of an optical-ultrasonic coupled continuous flow reactor to synthesize the insoluble α-bromoketone (4,4′-bis(2-bromoacetyl)biphenyl) is continuously produced in situ for synthesis, eliminating the need for large quantities of toxic bromine. A flowing cooling medium enhanced the ultrasound power transfer and eliminated the thermal effects of the ultrasound and light sources under TR = 2.1 min, T = 20 °C, and a flow cooling medium thickness of 1.5 cm. The reactants were converted to 92.4% and yielded up to 90.2%, significantly better than the batch reactor results. The experimental results show that the product particles are reduced considerably under ultrasound, eliminating the blockage. Free radical capture experiments investigated the stepwise bromination mechanism, kinetic parameters were calculated, and the reaction rate expressions derived from the basic steps were consistent with the kinetic model. These findings provide valuable insights into the reaction process, contributing to a more comprehensive understanding.