Lipase catalyzed synthesis of glucose palmitate in ionic liquid

Esterification of glucose and palmitic acid catalyzed by Novozyme 435 was carried out in three ionic liquids (IL): Cyphos 104, Cyphos 109 and [bmim][PF6]. To our knowledge this product has not been obtained in these ILs from these substrates up to now. The equilibrium conversion, as well as the amount of produced ester, were the highest in [bmim][PF6], i.e. X=77%, 0.115mmolg-1 of ester. Hence, this IL was chosen for further experiments. The enzyme was reused four times at 50 and 70°C to evaluate its stability in [bmim][PF6]. It was found that the enzyme activity slowly decreases at both temperatures. The reaction conditions in [bmim][PF6] were optimized to achieve the best reaction yield using the factorial design of experiments. The highest concentration of ester that could be achieved in the investigated variable range after 48h was 0.205mmolg-1 at 70°C, equimolar concentrations of substrates of 0.5mmolg-1 and 0.5% of water. Since it takes more than 48h to achieve equilibrium, the equilibrium ester concentration at optimal conditions is even higher, i.e. 0.254mmolg-1. The novelty of the present work lies in the use of IL as a solvent for the synthesis of sugar fatty acid ester, and particularly in the use of palmitic acid as an acyl donor in esterification with glucose in this solvent. © 2015 Elsevier Ltd