Abstract
The catalytic activity of Lewis acidic metal chlorides were screened for the production of biofuel precursor platform chemical, 5-hydroxymethylfurfural (HMF), from carbohydrates and biopolymers in aqueous and biphasic solvents under microwave and conventional heating methods. The screening of metal chloride catalysts for dehydration of several carbohydrate substrates revealed that Zr(O)Cl-2 catalyst is the most effective. Cheap and readily abundant Zr(O)Cl-2 catalyst produced 63% and 42% HMF from fructose and glucose, respectively, in water using methylisobutylketone (MIBK) as the organic phase in biphasic solvent system. The yield of HMF increased to 84% and 66% when Zr(O)Cl-2 catalyzed dehydration of fructose and glucose was carried out in [BMIM]Cl (1-butyl-3-methylimidazolium chloride)-MIBK biphasic solvent. H-1 NMR studies revealed that the dehydration reactions progressed through the formation of fructofuranose as an intermediate. Accordingly, a mechanism for isomerization of glucopyranose to fructofuranose has been proposed. The catalyst was recycled for five catalytic cycles without a significant loss in its activity. (C) 2013 Elsevier Ltd. All rights reserved.