Alkaline earth metal salts with environmentally friendly and economical have attracted attention in the process of biomass conversion, especially isomerization and dehydration. However, the lack of understanding of the alkaline...
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acidic catalysts play pivotal roles in the dehydration of hexose
into 5-hydroxymethylfurfural (HMF). However, these acidic catalysts
were usually exogenously added or self-made, which increase the cost
of preparation of HMF. Herein, a novel route to prepare HMF from high
fructose corn syrup (HFCS-55) using gluconic acid in situ produced
by bio-oxidation as a catalyst has been investigated. In the process
of bio-oxidation of HFCS-55, the introducing of ε-polylysine
(EPL) can effectively improve the acid tolerance of the coimmobilized
glucose oxidase and catalase. The immobilized enzymes can keep activity
in the existence of a large amount of gluconic acid. Through the chelation
of gluconic acid and calcium ions, the degree of gluconic acid ionization
was raised and enough protons were released to convert fructose to
HMF without the addition of acid. Using 2-methyltetrahydrofuran (2-MeTHF)
as an extractor and adding 2 wt % CaCl2, the HMF’s
yield reached 85% from fructose–gluconic acid mixture solution
at 150 °C for 10 min with 200 W microwave irritations. Furthermore,
we also used nuclear magnetic titration to investigate the complexation
mechanism of the calcium ion and gluconic acid.
Aminofurans are widely used in drug synthesis as aromatic modules analogous to aniline. However, unsubstituted aminofuran compounds are difficult to prepare. In this study, a process for the selective conversion of N‐acetyl‐d‐glucosamine (NAG) into unsubstituted 3‐acetamidofuran (3AF) is developed. The yield of 3AF from NAG catalyzed by a ternary Ba(OH)2−H3BO3−NaCl catalytic system in N‐methylpyrrolidone at 180 °C for 20 min can reach 73.9 %. Mechanistic studies reveal that the pathway to 3AF starts with a base‐promoted retro‐aldol condensation of the ring‐opened NAG, affording the key intermediate N‐acetylerythrosamine. Judicious selection of the catalyst system and conditions enables the selective conversion of biomass‐derived NAG into 3AF or 3‐acetamido‐5‐acetylfuran.
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