Influence of glucose solubility and dissolution rate on the kinetics of lipase catalyzed synthesis of glucose laurate in 2-methyl 2-butanol

The lipase catalyzed acylation of glucose by dodecanoic acid in 2-methyl 2-butanol was studied. The initial reaction rate was strongly dependent on the dissolved glucose concentration in the medium. Several methods were shown to increase dissolved glucose concentrations and initial reaction rates, namely, the use of solid beta-glucose, amorphous solid glucose, and supersaturated glucose solution. Supersaturated glucose solutions in 2-methyl 2-butanol showed a high stability even in the presence of solid crystalline glucose. During the reaction, the dissolved glucose concentration falls as the reaction proceeds, before recovering later as more of the excess solid dissolves. However, the ester synthesis rate continues to fall even after glucose concentration reaches its minimum, so glucose dissolution rate limitation is not responsible for the synthesis rate decline. Experiments with added molecular sieves show that the main reason is the accumulation of product water. In the presence of molecular sieves, 70% of glucose was converted to ester, independent of the initial soluble glucose in the medium. (C) 2002 Wiley Periodicals, Inc.