Enantioselective hydrogenation of dimethyl itaconate with immobilised rhodium-duphos complex in a recirculating fixed-bed reactor

Abstract

The catalytic hydrogenation of dimethyl itaconate was studied in lab-scale shake flask and transferred to continuous flow with recirculation in a trickle bed reactor. All experiments were performed under ambient conditions (20 °C and atmospheric pressure). The catalyst complex [Rh((R,R)-Me-DuPhos)(COD)]BF 4 was anchored to powder and trilobe alumina supports using phosphotungstic acid (PTA) as an anchoring agent. For the powder alumina, tests were conducted in the shake flask to ensure that the reaction was not influenced by mass transfer limitations by varying the stirrer speed and catalyst mass, thus ensuring the reported data are in the kinetic regime. In the shake-flask [substrate to catalyst molar ratio of 60, atmospheric pressure (101,317 Pa), room temperature (293.15 K), H 2 flow rate of 100 ml min −1 (1.7 × 10 −6 m 3 s −1) and agitation speed of 200 rpm], a turnover frequency (TOF) of 50 h −1 (1.4 × 10 −2 s −1) was achieved with powder alumina support in comparison to a TOF of 20 h −1 (5.6 × 10 −3 s −1) obtained with the trilobes. Under these conditions, the enantioselectivities obtained from immobilising the catalyst complex onto the powder and trilobe supports were 96% and 97%, respectively. Fitting Osborn–Wilkinson kinetics to the concentration profiles indicated that complexation with the olefin before reaction with hydrogen was the preferred path. The trickle bed reactor (TBR) was operated in the trickle flow regime using the trilobe support. Optimal gas and liquid flow rates were selected which were found to have a noticeable effect on initial reaction rate and enantioselectivity. Under optimized conditions in the TBR [substrate to catalyst molar ratio of 223, atmospheric pressure (101,317 Pa), room temperature (293.15 K), gas flow rate of 100 ml min −1 (1.7 × 10 −6 m 3 s −1) and liquid flow rate of 20 ml min −1 (3.3 × 10 −7 m 3 s −1)], 99% conversion and enantioselectivity of up to 99.9% were achieved.