Evolution Process of Humins Derived from Glucose

Abstract

The evolution process of humins derived from glucose was studied dynamically from the feedstock, the intermediates in solution, till humins solid formed. The key intermediates resulting in the formation of humins were identified, unveiling two elementary reactions including etherification of dehydrated glucose and electrophilic substitution of furfuryl alcohol (FAL). The characteristic IR peaks at 1583 and 1616 cm−1 could be attributed to the C=C conjugated with C=C and the C=C conjugated with C=O, respectively, whereas the shift from 1583 to 1616 cm−1 could be promoted by O2 or adding kojic acid. Unexpectedly, the participations of HMF and small aliphatic acids were excluded. Herein, through characterizations such as HPLC‐MS/MS, IR and SEM, the structural models of glucose‐derived humins at different temperatures and a successive growth diagram were proposed.

Selective catalytic oxidation of humins to carboxylic acids using the H4[PVMo11O40] Keggin-type polyoxometalate enhanced by alcohol doping and solubilizer

“…These signals could be assigned to the CC stretching vibration conjugated with carbonyl at 1600 cm −1 and the CO stretching vibration at 1700 cm −1 . 21,30 The described development of the signals is consistent with the formation mechanisms of humins postulated in the literature. 16,17,21,30,31 Accordingly, glucose dehydrates under acid catalysis in the first step to 5-hydroxymethylfurfural (5-HMF), which reacts further to obtain levulinic acid (LeA) under ring opening.…”

“…21,30 The described development of the signals is consistent with the formation mechanisms of humins postulated in the literature. 16,17,21,30,31 Accordingly, glucose dehydrates under acid catalysis in the first step to 5-hydroxymethylfurfural (5-HMF), which reacts further to obtain levulinic acid (LeA) under ring opening. In the studies by Wassenberg et al , 21 both intermediates were detected as part of the liquid reaction phase of the acid-catalyzed conversion of hexoses.…”

“…However, as mentioned above, there are a number of plausible formation mechanisms and proven structural elements for humins, which have led to various models for its structure. [15][16][17]29,30,57 According to these models, the furan-rich network is predominantly cross-linked via aliphatic bonds and has numerous active oxygen functionalities. In the study by Zandvoort et al, 29 2D NMR spectra were used to demonstrate that the linkers are not simple methylene groups, but rather short aliphatic chains and oxygen-functionalized bonds forming structures similar to levulinic acid, for example.…”

Creating Pores in Chitosan-Derived Humins via in Situ CO2 Formation

“…In our previous studies, we reported the formation of HMF and glucose-derived humins via a small-molecule mechanism. , In the present study, we report the fabrication of chitosan-derived humins by catalysis of weak acids via oligomer mechanism. The weak acids, such as OA and HOAc (Supporting Information, Figure S1), can only catalyze chitosan to obtain oligomers, whereas glucosamine monomer cannot be detected by NMR or HPLC.…”

“…Shen et al studied the formation mechanism of HMF-derived humins, revealing multiple elementary reactions such as etherification, esterification, aldol condensation, and acetalization . Recently, Shan et al proposed that glucose-derived humins were formed mainly through etherification of dehydrated glucose and electrophilic substitution of furfuryl alcohol . Our research demonstrated that controlling the humins structure was achievable.…”