(211g) The Influence of Solvent on Acid Catalyzed Dehydration of Model Polyols
The catalytic conversion of biomass and biomass-derived intermediates to energy-dense fuels and chemicals is often carried out in solvents or complex liquid mixtures. The reaction media can play an important role in influencing the catalytic molecular transformations. Herein we examine the catalytic dehydration of different model alcohols in solvent mixtures comprised of water and a polar organic solvent such as DMSO and GVL. Experiments along with theoretical simulations show that the acid-catalyzed dehydration reactions can be significantly promoted without product degradation by the appropriate choice of the solvent system. The net effect yields a significant improvement in both selectivity and reactivity over the reactions in these specific aqueous based systems. Molecular dynamics simulations were carried out to establish the faithful models of the co-solvent systems. These resulting structures provided input for more rigorous ab initio molecular dynamics simulations to follow the free energies changes for the detailed reaction paths involving proton addition, water elimination and proton abstraction to form the corresponding olefin products. The results show that the extent of solvation for different reactant alcohols can be rather different. There are non-uniform changes that occur with increasing the composition of the co-solvent or changing the alcohol reactant. In some cases there is a significantly lowering of activation barriers for the different alcohols while in others the barrier increases. These solvent effects were subsequently utilized to help promote the production of hydroxymethylfurfural (HMF) from fructose, while limiting the subsequent degradation of HMF to levulinic acid. The results provide important insights that may help to provide guidance into solvent selection for the selective production of targeted chemicals, along with the development of new acidic catalytic systems.