Dihydrolevoglucosenone can be prepared through the hydrogenation of unsaturated anhydrosugar levoglucosenone by using supported metal catalysts under mild conditions. Levoglucosenone is, at the same time, a chemical building block obtained by acid-catalysed pyrolysis at 300 °C of lignocellulosic biomass such as wood waste or sawdust. A significant amount of char is produced, as a by-product of LGO production, which can be used as fuel. When cellulose in tetrahydrofuran is heated to 210 °C with low concentrations of sulfuric acid in an autoclave, up to 51% levoglucosenone can be obtained through a solvent-assisted pyrolysis. Under optimized laboratory conditions, yields of up to 95% of levoglucosenone can be reached. Cellulose-containing waste from biorefineries can also be converted into 6-8% LGO under microwave irradiation at 180 °C for 5 minutes, in addition to the usual decomposition products such as hydroxymethylfurfural HMF, formic acid, formaldehyde, CO2 and water. Hydrogenation of the α, β-unsaturated ketone levoglucosenone with a metal catalyst such as palladium on alumina or palladium on zirconia leads selectively to Dihydrolevoglucosenone. Further hydrogenation can also yield tetrahydrofuran-2,5-dimethanol.
Properties
Dihydrolevoglucosenone is a clear colorless, to light yellow, liquid with a comparatively high dynamic viscosity of 14.5 cP and a mild, smoky ketone-like odor. It is miscible with water and many organic solvents. The compound is stable at temperatures up to 195 °C and weak acids and bases. H2-LGO reacts with inorganic bases via an aldol condensation mechanism. Dihydrolevoglucosenone is readily biodegradable and reacts to oxidants such as aqueous 30% hydrogen peroxide solution even at room temperature. Dihydrolevoglucosenone has a boiling point of 226 °C at 101.325 kPa, and a vapor pressure of 14.4 Pa near room temperature.
Applications
Dihydroglucosenone as a precursor
Dihydrolevoglucosenone can be used as a bio-based building block to produce a number of higher value chemicals such as drugs, flavours and fragrances and specialty polymers. The oxidation of dihydrolevoglucosenone with peracids such as peracetic acid in acetic acid produces optically pure 5-hydroxymethyldihydrofuranone , from which zalcitabine, formerly a HIV drug, is available. In a two-step hydrogenation process with a metal catalyst – first at 60 °C then at 180 °C – 1,6-hexanediol is mainly obtained via several intermediates. 1,6-hexanediol can be used as a starting material for the production of polyesters, polyurethanes and diamine 1,6-diaminohexane. At elevated temperature and in the presence of a palladium catalyst, hydrogenolysis of dihydrolevoglucosenone via levoglucosanol selectively yields tetrahydrofuran-2,5-dimethanol, which is a biodegradable solvent and a bio-based precursor to 1,6-hexanediol.
The search for alternative "green" solvents made from biomass or low-cost renewable raw materials, which are accessible through high-efficiency processes, in high yields, and meet the performance of conventional solvents, has triggered intensive research activities in industry and academia worldwide. Dihydrolevoglucosenone is considered a candidate as a "green" aprotic dipolar solvent. Several standard reactions of organic chemistry, e.g. Menshutkin reaction, Sonogashira coupling, Suzuki-Miyaura coupling, or the synthesis of organic ureas have been carried out in dihydroglucosenone.
Production
Circa Group produces dihydrolevoglucosenone from cellulose under the Cyrene brand and has built a 50-tonne demonstration plant with partners in Tasmania. The company estimates that dihydroglucosenone performs better than NMP in 45% and comparably to NMP in 20% of trials to date. Circa received authorization in 2018 from the European Chemicals Agency to produce or import up to 100 tonnes per year of dihydroglucosenone to the EU.
Literature
DS van Es: Study into alternative polar aprotic solvents. Wageningen University, Wageningen 2017.
JH Clark, A. Hunt, C. Topi, G. Paggiola, J. Sherwood: Sustainable Solvents: Perspectives from Research, Business and Institutional Policy. Royal Society of Chemistry, London 2017, .
