Insights into the NaCl-Induced Formation of Soluble Humins duringFructose Dehydration to 5-Hydroxymethylfurfural

NaCl is often added to facilitate phase separation for constructing aneffective biphasic solvent and promote the dehydration of biomass-derived fructoseto 5-hydroxymethylfurfural (HMF). In this work, we demonstrate that the presenceof NaCl in water leads to the occurrence of hydrogen bonding between Cl-andfructose, which inhibits the C-C cleavage of fructose, thereby alleviating theformation of unwanted oligomerized side products (i.e., soluble humins) throughthe degradative condensation pathway. In addition to the above positive effects, thepresence of NaCl in the aqueous solution also slows down the mutarotation offructose, increases the proportion of beta-fructopyranose tautomer, and facilitates theaggregation of fructose in solution, thereby favoring the formation of soluble huminsvia an etherification-dehydration-condensation path. This insightful understandingof the NaCl-induced formation of humins is of great importance for constructingsustainable solvent systems in future for inhibiting the formation of humins in HMFproduction.

Automated summary

The presence of NaCl in water inhibits the degradation of fructose and reduces the formation of unwanted byproducts, but promotes the formation of soluble humins.