Catalytic production of hexane-1,2,5,6-tetrol from bio-renewable levoglucosanol in water: effect of metal and acid sites on (stereo)-selectivity†
We report on a new route to produce hexane-1,2,5,6-tetrol (tetrol) from cellulose-derived levoglucosanol (lgol). We investigate the reaction intermediates formed over metal and acid catalysts, and propose a reaction network for this process. Lgol is converted to tetrol in up to 90% yield over a bifunctional Pt/SiO2–Al2O3 catalyst at 150 °C. High tetrol yields are maintained at lgol concentrations of up to 21 wt% in water. threo- and erythro-lgol first undergo hydrolysis to 3,4-dideoxymannose (DDM) and 3,4-dideoxyglucose (DDG), respectively. This reaction can be carried out selectively over an Amberlyst 70 acid catalyst at a temperature of 100 °C. At a higher temperature of 150 °C with no added catalyst, DDM and DDG undergo aldose–ketose isomerization to 3,4-dideoxyfructose (DDF). DDM is hydrogenated to cis-tetrol over a Pt/SiO2 catalyst, while DDG is hydrogenated to trans-tetrol. Formation of DDF erases the stereocenter at the C2 position of lgol, and hydrogenation of DDF produces a nearly 1 : 1 mixture of cis- and trans-tetrol. This catalytic approach to produce tetrol from biomass opens the door to sustainable chemicals derived from tetrol.