Homogeneous oxidation reactions of propanediols at low temperatures

Abstract

O2 reacts with propanediols via homogeneous pathways at 400-500 K. 1,2-Propanediol forms CH3CHO, HCHO, and CO2 via oxidative C-C cleavage and acetone via dehydration routes, while symmetrical 1,3-propanediol undergoes dehydration and oxidative dehydrogenation to form, almost exclusively, acrolein (ca. 90% selectivity). The products formed and their kinetic dependence on reactant concentrations are consistent with radical-mediated pathways initiated by O2 insertion into C-H bonds in a β position relative to oxygen atoms in diol reactants. Propagation involves β-scission reactions that form hydroxyl and hydroxyalkyl radicals. Acrolein/O2/H2O mixtures from the homogeneous oxidation of 1,3-propanediol form acrylic acid (with 90% yield) in tandem reactors containing molybdenum-vanadium oxide catalysts. These data reveal the unique reactivity of diols, compared with triols and alkanols, in homogeneous oxidations, while also providing useful insight into the molecular basis for reactivity in biomass-derived oxygenates.