(46e) Poly-L-Leucine Catalysed Chalcone Epoxidation in a Microstructured Peek REACTOR

The poly-L-leucine catalysed epoxidation of chalcone, which allows access to highly enantioselective chalcone epoxides, was investigated using organic solutions of hydrogen peroxide as the oxidation agent. The reaction system comprises of two processes, deprotonation of hydrogen peroxide and epoxidation. A suitable continuous tubular reaction protocol was previously established for this reaction system, achieving a conversion of 88.4 % and enantioselectivity of 88.8 %. Mixing was found to be critical due to the low diffusivity of the polymeric catalyst. In this work, a microstructured PEEK reactor with a footprint of 110 mm x 85 mm and production rate of ~ 0.5 g/day was designed and evaluated. The reactor consists of two micromixer-reactor configurations in series for the deprotonation and epoxidation reactions, with 30 minutes and 16 minutes residence times respectively. A staggered herringbone mixer design was selected for enhancing the mixing in the microstructured reactor. The effects of varying operating temperature, residence time and reactant concentrations on reaction performance in the microstructured reactor were investigated. The base case condition (13.47 g/l poly-L-leucine, 0.132 mol/l H2O2, 0.0802 mol/l chalcone, 0.22 mol/l 1,8-diazabicyclo[5.4.0]undec-7-ene) was found to be optimal, achieving a conversion of 86.7 % and enantioselectivity of 87.6 %. Several unexpected phenomena such as bubble clogging and increased viscosity due to the polymeric catalyst were encountered.