Polar aprotic solvent-water mixture as the medium for catalytic production of hydroxymethylfurfural (HMF) from bread waste.

Valorisation of bread waste for hydroxymethylfurfural (HMF) synthesis was examined in dimethyl sulfoxide (DMSO)-, tetrahydrofuran (THF)-, acetonitrile (ACN)-, and acetone-water (1:1v/v), under heating at 140°C with SnCl as the catalyst. The overall rate of the process was the fastest in ACN/HO and acetone/HO, followed by DMSO/HO and THF/HO due to the rate-limiting glucose isomerisation. However, the formation of levulinic acid (via rehydration) and humins (via polymerisation) was more significant in ACN/HO and acetone/HO. The constant HMF maxima (26-27mol%) in ACN/HO, acetone/HO, and DMSO/HO indicated that the rates of desirable reactions (starch hydrolysis, glucose isomerisation, and fructose dehydration) relative to undesirable pathways (HMF rehydration and polymerisation) were comparable among these mediums. They also demonstrated higher selectivity towards HMF production over the side reactions than THF/HO. This study differentiated the effects of polar aprotic solvent-water mediums on simultaneous pathways during biomass conversion.