Abstract
Continuous-flow mode enantiomer selective acetylations of racemic 1-phenylethanol, 1-cyclohexylethanol, and 1-phenylpropan-2-ol ( rac- 1a– c, respectively) with vinyl acetate were performed in small stainless steel packed-bed reactors filled with different commercial lipase preparations. In several lipase-filled columns, highly enantiomer selective ( E > 100) kinetic resolutions of these alcohols were achieved. In most cases, comparison of the continuous-flow and batch mode (shake flask) biotransformations indicated similar enantiomer selectivities ( E) but higher productivities (specific reaction rate: r) in the corresponding continuous-flow reaction. The effect of temperature (0–60 °C) and pressure (1–120 bar) on the continuous-flow acetylation of racemic 1-phenylpropan-2-ol was investigated in an immobilized Candida antarctica lipase B (CaLB) filled reactor. Pressure had no significant effect on r and E. Expectedly, a monotonous increase of specific reaction rate ( r) was observed within this temperature range. Most surprisingly, the enantiomer selectivity had a maximum ( E ∼ 25, at 20 °C) and a minimum ( E ∼ 7, at 50 °C). The continuous-flow reactions in CaLB-filled columns were successfully applied for preparative scale kinetic resolutions of rac- 1a– c.
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