dc.description.abstract | Lignin is a natural amorphous polymer most commonly found in woody biomass, and is mostly used as low value fuel for the paper industry. Recently however, the valorization of lignin has received increased attention, as its aromatic and highly functionalized structure provides possibilities for its conversion into fuels and useful chemicals.
Potential renewable platform molecules that can be obtained from lignin are catechols. Recently, the catalytic dioxygenation of pyrocatechol by a non-heme iron(III) complex containing the ligand tris(2-pyridylmethyl)amine (TPA), has been demonstrated. This reaction affords O-methyl-cis,cismuconic acid as main product, which can subsequently be converted to dimethyl adipate, a nylon-6,6 monomer.
While the iron(III)(TPA)catecholato complex catalyst showed excellent regioselectivity, a further increase in activity was desired. In this project, the influence of catalyst loading, temperature and oxygen pressure on dioxygenation activity and selectivity were investigated. The dioxygenation reaction was found to proceed at catalyst loadings as low as 0.1 mol% and a linear relationship for activity was observed for both temperature and pressure.
To improve the sustainability of this reaction, the possibility to change the solvent from methanol to a greener solvent, water, was tested. Another advantage of using water is that the conditions that can be safely used are more severe than for methanol. Therefore, the aim of this project was to synthesize and test a water-soluble TPA-derivative called bis(2-pyridylmethyl)((4-sulfo-2-pyridyl)methyl)amine (BPSA). Unfortunately, the synthesis of this ligand showed to be challenging and a purified ligand could not be obtained. Nonetheless, previously reported catalytic results in the dioxygenation of substituted catechol were reproduced. However, the unsubstituted pyrocatechol was not oxygenated with iron(III) complexes of BPSA using the similar reaction conditions as done in previous research with TPA, which indicates a lower reactivity for this ligand.
Finally, the hydrogenation of the oxygenated product mixture to adipic acid derivatives over non-noble metal catalysts was demonstrated with Raney nickel and with a synthesized Ni/CNF catalyst. | |