Biphasic conversion of bread waste to 5-hydroxymethylfurfural: Process optimization and isolation

A biphasic reaction system was developed to synthesize 5-hydroxymethylfurfural (HMF), a potential substitute for petroleum-based platform chemicals, from bread waste. Organic extractive phases, catalysts, and additives were first screened using starch as a model reactant. Methyl isobutyl ketone, dimethyl carbonate and ethyl acetate were examined as extractive phases, with dimethyl carbonate selected as the optimal solvent. The catalysts SnCl₄ and AlCl₃ were then tested alone and in combination with HCl, with SnCl₄ providing the highest yield and HCl having no effect; however, salt additives to the aqueous phase were shown to have a detrimental effect on the performance of SnCl₄-catalyzed reactions. The system was then optimized to afford 43 mol% HMF from starch in a 20 min reaction at 160 °C. HMF was synthesized from bread with a range of pre-treatments screened: untreated, liquid-nitrogen ground, oven dried, freeze dried, and extracted starch. Untreated bread gave the highest yield of 45 mol%, and leaving untreated bread to age for two weeks had no significant effect on the performance of the reaction. HMF produced from bread was purified by column chromatography, and isolated to afford a yield of 31 mol%.