摘要
The regioselective acylation of pyridoxine catalyzed by immobilized lipase () in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF) has been investigated, and compared with that in acetonitrile (ACN). The acetylation of pyridoxine using acetic anhydride in [BMIM]PF gave comparable conversion of pyridoxine to 5-monoacetyl pyridoxine with considerably higher regioselectivity (93%–95%) than that in ACN (70%–73%). Among the tested parameters, water activity () and temperature have profound effects on the reaction performances in either [BMIM]PF or ACN. For the reaction in [BMIM]PF, higher temperature (50°C–55°C) and lower (<0.01) are preferable conditions to obtain better conversion and regioselectivity. Mass transfer limitation and intrinsic kinetic from the ionic nature of ionic liquids (ILs) may account for a different rate-temperature profile and a lower velocity at lower temperature in [BMIM]PF-mediated reaction. Moreover, consecutive batch reactions for enzyme reuse also show that lipase exhibited a much higher thermal stability and better reusability in [BMIM]PF than in ACN, which represents another advantage of ILs as an alternative to traditional solvents beyond green technology.
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