ABSTRACT
Levoglucosenone (LGO) is the major product formed when cellulose is pyrolyzed in the presence of acid at temperatures between 170 and 350 °C. The current intense interest in biomass conversion has led to a number of reports on its preparation; however, there is still uncertainty on the mechanism leading to LGO. We propose a new mechanism which involves a C2-C1 hydride shift followed by intramolecular trapping of a dioxyallyl cation. The reaction has been modeled using DFT calculations from the known LGO precursors levoglucosan and 1,4:3,6-dianhydro-α-D-glucopyranose to a common intermediate with calculated barriers of 10.6 and 13.5 kcal·mol-1, respectively. A discussion of the literature on the formation of LGO from late pathway intermediates is also provided.
ABSTRACT
Novel thin and smooth deuterated cellulose films were synthesised to visualize adsorbed bio-macromolecules using contrast variation neutron reflectivity (NR) measurements. Incorporation of varying degrees of deuteration into cellulose was achieved by growing Gluconacetobacter xylinus in deuterated glycerol as carbon source dissolved in growth media containing D2O. The derivative of deuterated cellulose was prepared by trimethylsilylation(TMS) in ionic liquid(1-butyl-3-methylimidazolium chloride). The TMS derivative was dissolved in toluene for thin film preparation by spin-coating. The resulting film was regenerated into deuterated cellulose by exposure to acidic vapour. A common enzyme, horseradish peroxidase (HRP), was adsorbed from solution onto the deuterated cellulose films and visualized by NR. The scattering length density contrast of the deuterated cellulose enabled accurate visualization and quantification of the adsorbed HRP, which would have been impossible to achieve with non-deuterated cellulose. The procedure described enables preparing deuterated cellulose films that allows differentiation of cellulose and non-deuterated bio-macromolecules using NR.
Subject(s)
Cellulose/chemistry , Deuterium/chemistry , Horseradish Peroxidase/chemistry , Adsorption , Deuterium Oxide/chemistry , Deuterium Oxide/metabolism , Gluconacetobacter/growth & development , Gluconacetobacter/metabolism , Horseradish Peroxidase/metabolism , Imidazoles/chemistry , Microscopy, Atomic Force , Neutron Diffraction , Spectroscopy, Fourier Transform Infrared , Trimethylsilyl Compounds/chemistryABSTRACT
With the increasing restriction and control of hazardous solvents, safer alternatives need to be identified. Here a contemporary approach to solvent selection and substitution is presented that offers a more scientific alternative to the simple "like-for-like" exchange. A new family of levoglucosenonederived compounds is proposed, modeled to determine their solvent properties, synthesized, and tested. These new molecules show promise as replacements for polar aprotic solvents that have chronic toxicity issues, such as dichloromethane, nitrobenzene, and N-methylpyrrolidinone. The success of this approach makes it possible for academia and industry to make calculated, intelligent choices for solvent substitution in the future.
Subject(s)
Bridged Bicyclo Compounds, Heterocyclic/chemistry , Glucose/analogs & derivatives , Solvents/chemistry , Cost-Benefit Analysis , Glucose/chemistry , Green Chemistry Technology/economicsABSTRACT
Chiral epoxides-such as ethyl and methyl (S)-3-(oxiran-2-yl)propanoates ((S)-1a/1b)-are valuable precursors in many chemical syntheses. Until recently, these compounds were synthesized from glutamic acid in four steps (deamination, reduction, tosylation and epoxide formation) in low to moderate overall yield (20%-50%). Moreover, this procedure requires some harmful reagents such as sodium nitrite ((eco)toxic) and borane (carcinogen). Herein, starting from levoglucosenone (LGO), a biobased chiral compound obtained through the flash pyrolysis of acidified cellulose, we propose a safer and more sustainable chemo-enzymatic synthetic pathway involving lipase-mediated Baeyer-Villiger oxidation, palladium-catalyzed hydrogenation, tosylation and treatment with sodium ethoxide/methoxide as key steps. This route afforded ethyl and methyl (S)-3-(oxiran-2-yl)propanoates in 57% overall yield, respectively. To demonstrate the potentiality of this new synthetic pathway from LGO, the synthesis of high value-added (S)-dairy lactone was undertaken from these epoxides and provided the target in 37% overall yield from LGO.
Subject(s)
Bridged Bicyclo Compounds, Heterocyclic/chemistry , Epoxy Compounds , Glucose/analogs & derivatives , Lactones/chemistry , Propionates , Epoxy Compounds/chemical synthesis , Epoxy Compounds/chemistry , Glucose/chemistry , Propionates/chemical synthesis , Propionates/chemistryABSTRACT
Dihydrolevoglucosenone (Cyrene) is a bio-based molecule, derived in two simple steps from cellulose, which demonstrates significant promise as a dipolar aprotic solvent. The dipolarity of dihydrolevoglucosenone is similar to NMP, DMF and sulpholane. Dihydrolevoglucosenone demonstrates similar performance to NMP in a fluorination reaction and the Menschutkin reaction.
Subject(s)
Bridged Bicyclo Compounds, Heterocyclic/chemistry , Cellulose/analogs & derivatives , Halogenation , Models, Molecular , Solvents/chemistryABSTRACT
Bleached kenaf handsheets sized with different polymers such as chitosan, polyvinyl alcohol and cationic starch, were used for the determination of surface topography. A non-contact profilometer, the AltiSur 500, was used to characterize the topography of structural details in the paper surface. Numerical and visual characterization of surface roughness indicated that the surface of chitosan-sized paper was less rough than other surfaces, and all the sized papers were commonly smoother than the unsized paper. One property of bio-polymer of chitosan is its ability to form films that improve the surface properties of paper when it is applied to the surface of the sheet.