Reaction media dominated product selectivity in the isomerization of glucose by chromium trichloride: From aqueous to non-aqueous systems

• Fructose yield follows a general curve in water independent of reaction variables.
• Tuning the solvent is the most effective approach to change the product distribution.
• Control experiments and UV–vis analyses provide preliminary mechanistic insights.

While chromium trichloride hydrate (CrCl3·6H2O) effectively catalyzed the isomerization of glucose into fructose in aqueous solution, a general product selectivity behavior was observed independent of reaction variables such as reaction time, temperature, catalyst loading, halide ion, and initial glucose concentration. By studying the mixed solution of dimethylsulfoxide (DMSO) and water at varied DMSO/H2O ratios, it was found that deviation from the general water-phase fructose yield curve, with concomitant 5-hydroxymethylfurfral (HMF) formation, occurred when the fructose concentration in available water became sufficiently high in DMSO rich solvent mix. Therefore, tuning the solvent system was the most effective approach to change the product distribution from CrCl3·6H2O catalyzed glucose conversion. The apparent activation energy of glucose conversion in the studied system was estimated to be 58.6 kJ mol−1. Special attention was also given to gain some mechanistic insights by control experiments with simple model compounds and additives, 13C NMR and UV–vis spectroscopic analyses.

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