Conversion of carbohydrates and lignocellulosic biomass into 5-hydroxymethylfurfural using AlCl₃·6H₂O catalyst in a biphasic solvent system

Abstract

AlCl3·6H2O in a biphasic medium of water/tetrahydrofuran (THF) is effective for the synthesis of 5-hydroxymethylfurfural (HMF) from glucose-based carbohydrates. For glucose, an HMF yield of 61% was achieved in 10 min at 160 °C under microwave heating. The reaction time profile revealed the intermediacy of fructose en route to HMF with a dehydration rate constant that is approximately 4 times that of glucose isomerization to fructose. Addition of NaCl did not increase HMF yields significantly but it diminished lactic acid formation. Disaccharides (maltose and cellobiose) and starch gave good yields of HMF. However, cellulose required a higher temperature (180 °C) and longer reaction time (30 min) to give a modest yield of 37%. Several lignocellulosic biomass variants (corn stover, pine wood, grass, and poplar) were investigated with the AlCl3·6H2O biphasic system. The yields of HMF were modest (20–35%) but high concurrent yields of furfural were observed (51–66%). The described AlCl3·6H2O–NaCl–H2O/THF biphasic medium has potential because it is economic, nontoxic, and it exhibits fast kinetics (10 min) under microwave heating.