Dynamic Kinetic Resolution of Secondary Alcohols Combining Enzyme‐Catalyzed Transesterification and Zeolite‐Catalyzed Racemization

• Published in: Chemistry – A European Journal
• Main Authors: Zhu, Yongzhong, Fow, Kam‐Loon, Chuah, Gaik‐Khuan, Jaenicke, Stephan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2006
• Subjects: General Chemistry; Catalysis; Organic Chemistry; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1002/chem.200600723; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fchem.200600723; https://onlinelibrary.wiley.com/doi/full/10.1002/chem.200600723

Abstract Hydrophobic zeolite beta containing low concentrations of Zr or Al was found to be a good catalyst for the racemization of 1‐phenylethanol. The formation of styrene as a side product could be minimized by reducing the metal concentration in the zeolite beta. Combined with an immobilized lipase from Candida antarctica , the dynamic kinetic resolution of 1‐phenylethanol to the ( R )‐phenylethylester can be achieved with high yield and selectivity. The reaction was best conducted in toluene as solvent at 60 °C, with higher temperatures leading to a loss in the enantioselectivity of the formed ester. By using high‐molecular‐weight acyl‐transfer reagents, such as vinyl butyrate or vinyl octanoate, a high enantiomeric excess of the product esters of 92 and 98 %, respectively, could be achieved. This is attributed to a steric effect: the bulky ester is less able to enter the pore space of the zeolite catalyst where the active sites for racemization are localized. Close to 100 % conversion of the alcohol was achieved within 2 h. If the more common acyl donor, isopropenyl acetate, was used, the enantiomeric excess ( ee ) of the formed ester was only 67 %, and the reaction was considerably slower.