Fructose Epimerization to l-Sorbose in Water over Molybdenum Oxide: Reaction Kinetics and Mechanism Insights

Herein, we report the significant production of l-sorbosevia a chemical catalysis method over molybdenum oxide (MoO3) using fructose in a water medium. The heterogeneous catalytic setupcould produce 32% l-sorbose and 55% selectivity via C5-fructoseepimerization. However, the synthesis was accompanied by a minor formationof tagatose (& SIM;4%) and allulose (& SIM;1%) side products via1,3-hydride shift and 1,2-hydride shift mechanisms, respectively,using the single fructose source. Moreover, the interconversion reaction(fructose-sorbose) exhibited temperature-dependent characteristics,with an activation barrier of 68.2 kJ/mol. Based on the kinetics,fructose is shown to have a preference for reaching equilibrium withsorbose, which forms through a single 1,4-hydride shift. Due to this,a delayed formation of side products was observed, which follows aseries of hydride shifts between the intermediates. From the results,the catalyst is versatile for various epimerization reactions. Selectiveextraction of fructose from the postreaction medium for product enrichmentvia naphthalene-2-boronic acid liquid-liquid, however, resultedin the recovery of both fructose and sorbose (ketoses) because ofidentical characteristics. Thus, the catalytic setup represents anenvironmentally friendly and sustainable method for upscaling basedon the process's green matrices.

Automated summary

In this study, a significant production of l-sorbose through chemical catalysis over molybdenum oxide was reported. The catalytic setup yielded 32% l-sorbose with a selectivity of 55% via C5-fructose epimerization. However, minor formation of tagatose and allulose side products was observed due to hydride shift mechanisms. The interconversion reaction between fructose and sorbose was found to be temperature-dependent.