3-acetamido-5-acetylfuran from n-acetyl-d-glucosamine: its synthesis, properties and applications

Liu, Yi (2017) 3-acetamido-5-acetylfuran from n-acetyl-d-glucosamine: its synthesis, properties and applications. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

In recent years, biomass has been developed as a resource for production of biofuels and renewable chemicals. 5-Hydroxymethylfurfural (5-HMF) is an important platform compound for a variety of value-added chemicals. 5-HMF can be obtained from the dehydration of lignocellulosic biomass such as fructose, glucose, sucrose and cellulose. There have been numerous studies on the synthesis of 5-HMF, among which many were focused on the mechanisms. The tools and approaches used for mechanistic studies on the transformation of biomass to 5-HMF were reviewed, showing that both lab techniques (e.g. NMR spectroscopy, kinetic studies) and computational calculations can be used for intermediate detection and mechanism investigation. It is proposed that the methods used with this class of renewable feedstock will be valuable in studying the reactions of related nitrogen-containing carbohydrates. N-Acetyl-D-glucosamine (NAG) is an amino sugar and the monomer of chitin, which occurs abundantly in the shells of crustaceans. The dehydration of NAG produces a renewable amide, 3-acetamido-5-acetylfuran (3A5AF). When ionic liquids (ILs) were used as solvents, the 3A5AF yield was influenced by the acidity of the ILs. The addition of boric acid (B(OH)₃) and sodium chloride (NaCl) improved the 3A5AF yield. Ethyl acetate (EtOAc) was added for in situ extraction of 3A5AF during the reaction, and an optimum yield of 55.6% was achieved. Kinetic studies were performed for the dehydration of NAG and its two isomers (NAGal, NAMan) in the presence of B(OH)₃. Chromogen I and III were proposed as important intermediates in the mechanism, as their characteristic peaks were observed in the ¹H NMR spectra of NAG dehydration. ¹¹B NMR spectroscopy was performed to study the role of B(OH)₃ in the dehydration of NAG. The reusability of [Bmim]Cl in the conversion of NAG to 3A5AF was studied. The pKa of 3A5AF was determined through both computational calculations and experimental measurements. The solubility of 3A5AF in supercritical carbon dioxide (scCO₂) was low, mainly due to the strong intermolecular forces between 3A5AF molecules. Dimerization energies of 3A5AF were calculated, and IR and NMR analyses were performed to investigate the hydrogen bonding. The highest occupied molecular orbital, lowest unoccupied molecular orbital, electrostatic potential and atomic charges of 3A5AF were determined through molecular orbital calculations. A reaction between 3A5AF and a methyl Grignard reagent was performed to study the reactivity of the two carbonyl carbons towards a nucleophile. Hydrolysis of 3A5AF was performed via sodium hydroxide (NaOH) catalysis and an amino-substituted furan product was obtained. Reduction of the acetyl group in 3A5AF was achieved using sodium borohydride (NaBH₄) or catalytically via transferhydrogenation using an iridium (Ir) catalyst. 3A5AF and the hydrolysis product were tested for CO₂ capture, but no reaction was observed because of their inherent acidity. Tautomerism of 3A5AF was observed in methanol-d4 (CD₃OD) as evidenced by H-D exchange within the acetyl group.

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