Optimization of benzoin synthesis in supercritical carbon dioxide by response surface methodology (RSM)

alpha-Hydroxy ketones are important precursors for biologically active compounds, especially benzoins have important applications in chemistry and pharmacy. In this study enantioselective synthesis of benzoin was studied in supercritical carbon dioxide (SCCO2). Response surface methodology (RSM) was used to investigate the effects of temperature (T), pressure (P) and pH on enantiomeric excess of chiral benzoin using Candida cylindracea lipase in SCCO2. A 2(3) factorial design was performed to optimize the chiral benzoin synthesis. The optimum conditions were found as 40 degrees C, 79 bar, pH 6.4 and at these conditions enantiomeric excess (ee) was obtained as 62% (R-benzoin). At the optimum conditions, bases such as DMAP (4-dimethylaminopyridine) and triethylamine were added to reaction medium to increase kinetic resolution. The addition of DMAP considerably enhanced the enantiomeric excess (80% S-benzoin), while triethylamine had negative effect on ee. (C) 2008 Elsevier B.V. All rights reserved.