Unexpected phosphate salt-catalyzed hydrolysis of glycosidic bonds in model disaccharides: Cellobiose and maltose

摘要

Monobasic sodium phosphate salt is shown to unexpectedly catalyze cellobiose and maltose hydrolysis to glucose at temperatures between 90 °C and 120 °C and pH 4 in aqueous solution. A selectivity of up to 80% glucose is achieved, which increases with increasing disaccharide dilution. The catalytic role of the phosphate salt is evident in a comparison of the measured activation energy of the catalyzed process for cellobiose hydrolysis of 59 kJ mol~(-1) versus that reported for the background reaction of 136 kJ mol~(-1). The normalized rate of catalysis over background significantly increases further at higher pH. Zero-order dependence of hydrolysis rate on disaccharide concentration as well as a logarithmic dependence of hydrolysis rate on phosphate salt concentration is observed. A heterogeneous catalysis mechanism is proposed, which is supported by the presence of condensed phosphate in reaction solution via ~(31)P NMR spectroscopy. This mechanism involves disaccharide chemisorption and subsequent activation via interactions with surface acid/base sites.