Utilization of Biomass Derived Furans in Value-Added Organics and Heterogeneous Oxorhenium Catalysts for Deoxydehydration of Diols (2013)

As fossil fuels are depleted, there is a growing focus on renewable chemicals based on biomass materials, including both fuels and chemical feedstocks. Current methods for biomass utilization include biological conversion to produce ethanol and various thermochemical routes (gasification, pyrolysis, liquefaction, hydrothermal treatment, etc.). Furfural is one particular chemical that can be obtained from lignocellulosic biomass in good yields through the dehydration of sugar residues. It can be used as a feedstock for chemicals such as furan and THF, or as a platform molecule for making liquid fuels. The objective of this research is to investigate new pathways for the utilization of furfural in value-added products. In addition, heterogeneous oxorhenium catalysts were studied for deoxydehydration of vicinal diols, a reaction relevant to the conversion of biomass derived sugars. A cationic oxorhenium(V) oxazoline was studied for the catalytic condensation of diols or epoxides with aldehydes. Here, reactions were done under neat conditions and mild temperatures, achieving good to excellent yields of the 1,3-dioxolane products. The reaction conditions were then applied to the biorenewables furfural and glycerol, providing the first reported solvent-free condensation of these materials. Investigation into the stereoselectivity of the reaction reveals divergent pathways for the reaction of epoxides versus the analogous diol. The coupling of furfural with glycerol is further investigated. Neat conditions are developed to provide the cyclic acetal products, using simple Lewis acid salts and heterogeneous acid catalysts. Since the reaction is performed under neat conditions, novel reaction methods are studied in order to remove the water byproduct and drive the reaction forward. We found these reaction conditions to be applicable to crude glycerol. The resultant acetals were isolated and modified via hydrogenation and acetylation. These materials were then studied as blending agents with biodiesel, aiming to improve the low temperature properties. While no benefit was observed, the data does not preclude the use of these materials as additives in biodiesel. The homocoupling of furfural is then studied using the N-heterocyclic carbene catalyzed benzoin condensation. Here, green methods are focused on with the ultimate goal of realizing the two-step process of producing furfural and subsequently performing the homocoupling. The C10 product, furoin, serves as a good platform for the production of alkane fuels, and several processes are investigated to reach this goal. Finally, the deoxydehydration of vicinal diols using oxorhenium catalysts is known using several methods with various reductants. A number of known heterogenous oxorhenium catalysts have been described and studied for oxidation type reactions. We prepared several of these catalysts and studied them for the known diol reduction reactions. However, good results were not obtained, with the rhenium either being inactive or exhibiting significant leaching from the support, hence limiting the recyclability of the catalyst material.