Low melting systems consisting of ammonium salts and highly concentrated fructose were used for the conversion of fructose into 5-hydroxymethylfurfural (HMF). Not only acting as solvents, at sufficiently high temperatures, the ammonium salts themselves could also catalyse the dehydration of fructose to HMF. Among those salts, tetraethyl ammonium chloride (TEAC) was found to be the most efficient solvent-catalyst, demonstrated by its ability to achieve 81.3% HMF yield with 33.3 wt% fructose concentration at 120 degrees C, 79.2% HMF yield was obtained with 50 wt% fructose concentration in the TEAC/fructose system using 5 mol% NaHSO4 center dot H2O as a co-catalyst. A semi continuous biphasic system of TEAC/fructose/NaHSO4 center dot H2O melt using tetrahydrofuran (THF) to recover HMF was proposed and demonstrated in a laboratory scale process operating at 120 degrees C. The impurities in the HMF recovered, involving TEAC and NaHSO4 center dot H2O. were determined using H-1 NMR, elemental analysis and ICP-OES. (C) 2011 Elsevier B.V. All rights reserved.