PhD Oral Defence - Franklin Chacón Huete, Chemistry

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The high demand and uncontrolled use of petroleum feedstocks has had a tremendous negative impact on the environment. Nowadays, much attention is being paid to biomass as a source of organic starting materials, and the U.S. Department of Energy has highlighted furans derived from hemicellulose as potential building blocks for chemical synthesis, such as 5-hydroxymethyl furfural (HMF 3) and 2,5-furandicarboxylic acid (FDCA 6). The development of new tools that allow the use of these readily available compounds as starting materials in the construction of complex molecules is necessary for the transition of industrially scaled productions from a petroleum-based chemistry to a biomass-based alternative. The synthesis of high-value biomass derived 2,5-diaryl furans (190) has been achieved successfully from good to excellent yields with a wide scope of coupling partners of aryl halides and FDCA (6). Keeping in mind that FDCA comes from the direct oxidation of HMF (3), a route to access 2,5-non symmetric furans (30) was achieved utilizing the latter molecule as starting material. Selective oxidation of the aldehyde moiety has not been reported under mild and accessible conditions, therefore, a solvent-free mechanochemical assisted selective oxidation was studied to synthesize the required 5-hydroxymethyl-2-furoic acid (HMFA 4) and 2,5-dihydroxymethyl furan (5), in a base-promoted disproportionation, reducing the reaction times to only 5 min and with an Efactor of only 0.5. Decarboxylative cross-coupling and oxidation of the alcohol moiety allowed access to an alternative substrate for the decarboxylative cross-coupling, achieving the convenient synthesis of 2,5-diaryl non-symmetric furans (30). Additionally, the versatile intermediate 5-hydroxymethyl-2-aryl furan (216) was utilized to synthesize bis(5-arylfuran-2-yl)methane (223) scaffolds in good to excellent yields. Future work includes efforts to use decarboxylative cross-coupling reactions between FDCA (6) and dihalide aryl systems (235) to produce conjugated furan co-polymers (236).