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

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 31P NMR spectroscopy. This mechanism involves disaccharide chemisorption and subsequent activation via interactions with surface acid/base sites.