Selective catalytic transformations of non-edible carbohydrates

Carbohydrates are nature’s main biomass constituent, and have already shown to be suitable starting materials for the production of a wide variety of bio-based chemicals. Many agro residues, such as sugar beet pulp, still contain valuable carbohydrates. The aim of my project is to selectively convert these non-edible carbohydrates into useful chemical building blocks.

Highlight of the past year

Furan-2,5-dicarboxylic acid (FDCA) is an interesting bio-based building block with applications ranging from polyesters and polyamides to plasticizers. In order to prevent the use of food-grade sugars for the production of FDCA, there is an increasing drive towards the use of non-food feedstocks. We developed a novel route to 2nd generation FDCA starting from uronic acids, which are abundantly present in agro residues like sugar beet pulp and citrus peels.

In aqueous solution uronic acids are mainly present in the pyranose form (6-membered ring), which prevents direct acid catalyzed cyclodehydration to 5-membered furans, giving undesired degradation instead. Our aim was to investigate if uronic acids can be selectively isomerized to their keto-isomers, which preferentially adapt a furanose form (5-membered ring), allowing for selective cyclodehydration to furans.

A base catalyzed isomerization of uronic acids gave the corresponding 5-keto-aldonic acids (5-KA) in high yield by selective precipitation of the Ca-salts. Subsequent acid catalyzed dehydration of 5-KA in alcoholic solvents gave formylfuroic acid (FFA) esters in good yield and high purity. Control experiments showed that FFA is not formed from the uronic acids, which shows the benefit of the isomerization step. Finally an oxidative esterification of FFA over supported Au-catalysts gave the desired FDCA esters, again in high yield and selectivity.

Type of student projects envisioned

Student projects all involve organic chemistry and/or catalysis orientated lab work, focused on the conversion of carbohydrates. Standard analysis during synthesis includes NMR, GC-MS, IR and HPLC. Catalysts will be analyzed by TEM, XRD, chemisorption and physisorption.