Branched Diol Monomers from the Sequential Hydrogenation of Renewable Carboxylic Acids

A prominent challenge in replacing petrochemical polymers with bioderived alternatives is the efficient transformation of biomass into useful monomers. In this work, we demonstrate a practical process for the synthesis of multifunctional alcohols from five-and six-carbon acids using heterogeneous catalysts in aqueous media. Design of this process was guided by thermodynamic calculations, which indicate the need for two sequential high-pressure hydrogenations: one, reduction of the acid to a lactone at high temperature; two, further reduction of the lactone to the corresponding diol or triol at low temperature. For example, the conversion of mesaconic acid into (alpha or beta)-methyl-gamma-butyrolactone was achieved with 95% selectivity at a turnover frequency of 1.2 min(-1) over Pd/C at 240 degrees C. Subsequent conversion of (alpha or beta)-methyl-gamma-butyrolactone into 2-methyl-1,4-butanediol was achieved with a yield of 80% with Ru/C at 100 degrees C. This process is an efficient method for the production of lactones, diols, and triols, all valuable monomers for the synthesis of bioderived branched polyesters.