Novel dehydration of carbohydrates to 5-hydroxymethylfurfural catalyzed by Ir and Au chlorides in ionic liquids

Catalytic dehydration of carbohydrates into 5-hydroxymethylfurfural (5-HMF) has been studied in the presence of ionic liquids, i.e., 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) and triethylamine sulphate ([Et(3)NH][HSO(4)]) using metal salts as catalysts. Novel metal chlorides IrCl(3) and AuCl(3)center dot HCl as catalysts in ionic liquid showed remarkable activity and selectivity to 5-HMF for the reaction of fructose dehydration. The reaction conditions of fructose dehydration were optimized as follows: reaction temperature 120 degrees C, reaction time 30 min, IrCl(3) content 7% (mol% based on fructose) in [BMIM]Cl, at which the conversion of fructose and the yield of 5-HMF reached 97.7% and 89.0%, respectively. By simply assuming the fructose simultaneously converts to 5-HMF and other by-products by the first-order reaction kinetics, the energies of activation are estimated to be 165 kJ/mol for the formation of 5-HMF and 124 kJ/mol for the formation of other by-products from 80 to 100 degrees C, respectively. The existence of water in the media more than 0.5% (v/v) would significantly slow down the dehydration rate of fructose, while it seemed not necessary to further remove water during the reaction when the water was less than 0.5%. Compared with the dehydration of fructose, the dehydration of other carbohydrates such as glucose, sucrose and maltose was rather difficult. (C) 2010 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.