Selectivity and Lifetime Effects in Zeolite-Catalysed Baeyer-Villiger Oxidation Investigated in Batch and Continuous Flow

In this manuscript, we investigate the kinetic, mechanistic and lifetime aspects of the Baeyer-Villiger oxidation of cyclohexanone with Sn-beta as catalyst and H2O2 as oxidant, with the aim of: 1) elucidating the overall reaction network, 2) closing the carbon balance, particularly at high levels of conversion, and 3) examining the intensification of this process in the continuous regime. The results presented herein conclusively demonstrate that this reaction is highly selective for the desired product (epsilon-caprolactone) only below conversions of 60 %. Above this level of conversion, unavoidable hydrolysis of epsilon-caprolactone to 6-hydroxyhexanoic acid is observed, which consumes the desired product and leads to a reduction in catalytic activity through poisoning. By elucidating the reaction network and working under optimised conditions, we show the potential viability of this methodology to operate continuously over a 180 h period, both at high levels of productivity (324 g (cyclohexanone converted) cm(-3) (reactor volume) kg(-1) (catalyst) h(-1)) and selectivity (70% at 60% conversion). Over 5000 substrate turnovers were observed during this period, an order of magnitude higher than previously noted for this particular catalyst system.