Industrial & Engineering Chemistry Research, Vol.53, No.2, 635-642, 2014
Rapid Base-Catalyzed Racemization of (R)-Ibuprofen Ester in Isooctane-Dimethyl Sulfoxide Medium with Improved Kinetic Model
The synthesis of chiral compounds through dynamic kinetic resolution has shown improved results with the presence of racemization. Integrating the reaction media for biocatalytic kinetic resolution and base-catalyzed racemization pose challenges in chiral separation due to its alkaline environment. Base-catalyzed racemization of (R)-ibuprofen ester has been separately studied in isooctane, isooctane water, and isooctane DMSO media. A rapid racemization rate of (R)-ibuprofen ester was obtained in isooctane-DMSO medium as compared with the other two media with racemization rate constants (k(rac)) of 0.292 and 0.001 h(-1), respectively. An investigation carried out on sodium hydroxide and Amberlyst A26 (OH- resin) as base catalysts has shown that Amberlyst A26 gave a better performance compared to that of sodium hydroxide. Additionally, the rate of racemization increases at higher reaction temperatures, but shows otherwise at a higher concentration of substrate. The kinetic model of the base-catalyzed racemization was developed and experimentally validated. The model incorporates two main contributing factor's in the racemization reaction: a base catalyst and initial substrate concentrations. Base-catalyzed racemization was conducted in the proposed packed-bed reactor, where the racemization rate was faster with an increased velocity of feed flow rate. The absolute rate constants of racemization (k(abs)) obtained were 0.112 and 0.275 h(-1) for feed flow rates of 0.6 and 1.2 mL. min(-1), respectively. The packed-bed reactor was then proposed to be coupled with a membrane reactor as an integrated dynamic kinetic resolution reactor of chiral compounds.