Abstract
Chemical processes capable of reducing the high oxygen content of biomass-derived polyols are in demand in order to produce renewable substitutes for chemicals of fossil origin. Deoxydehydration (DODH) is an attractive reaction that in a single step transforms a vicinal diol into an alkene but the reaction requires a homogeneous catalyst, a reductant and a solvent, which are typically expensive, unsustainable, or inefficient Herein, we present the use of molybdenum(VI)-based compounds, in particular the cheap and commercially available (NH4)(6)Mo7O24 center dot 4H(2)O, as catalysts for the DODH of vicinal diols in isopropyl alcohol ((PrOH)-Pr-i), which serves as both the solvent and reductant. The reaction proceeds at 240-250 degrees C in a pressurized autoclave, and the alkene yield from simple aliphatic diols can be as high as 77%. The major byproducts are carbonyl compounds formed by dehydration of the diol and the alcohols formed by transfer hydrogenation of the carbonyl compounds; the total yield of reduced species (i.e, alkene alcohols) can be as high as 92%. The DODH of glycerol yields allyl alcohol, Which undergoes subsequent Mo-catalyzeddeeoxygenation to propylene driven by the oxidation of (PrOH)-Pr-i; a major byproduct is the homocoupled product 1,5-h-exadiene. Further insight in this Mo-catalyzed deoxygenation is gained by an investigation of Model compounds: The allylic alcohol 1-hexen-3-ol is deoxygenated to hexene isomers in a yield of 65%, while benzyl alcohol is deoxygenated to toluene in a yield of 93%. The DODH of erythritol yields 39% 2,5-dihydrofuran, while the DOOR of the proposed intermediate 1,4-anhydroerythritol yields 75%. The mechanism of the DODH of 1,4-anhydroerythritol was investigated by means of density functional theory (DFT), and the rate-determining step (24.1 kcal/mol) was found to be reduction of a,molybdenum(VI) diolate to a molybdenum(IV) diolate.