Production and transformation of organic compounds from renewable feedstock : Catalytic approaches

Abstract

This thesis is focused on the development of strategies for lignocellulosic biomass valorization. The thesis consists of two parts. The first part of the presented work is related to the catalytic fractionation of biomass (lignin-first approach) and the production of monomeric compounds from lignocellulose. In the first project (Chapter 2) we have established a process to study the transformations occurring during the catalytic organosolv pulping of wood in the presence of Pd/C. This was achieved by performing a fractionation under continuous-flow conditions. In the designed process, the pulping and the transition metal catalyzed reactions were separated in space and time. Thus, the role of the solvolysis and the transfer hydrogenation reactions were studied independently. We discovered that during the solvolysis of wood, a substantial amount of monomeric lignin fragments are released into the solution. The main role of the catalyst is to stabilize these monomers and prevent their repolymerization. Based on the obtained knowledge we developed a new version of the lignin-first approach (Chapter 3). In this process zeolites were used as shape-selective catalysts. We have demonstrated that by tuning the size of pores of the catalyst the undesirable bimolecular reactions can be minimized. Furthermore, the released monomers can be converted into stable products via transfer hydrogenation reactions.   The second part is related to studies of dimeric and trimeric lignin model compounds. In Chapter 4, the reactivity of the dibenzodioxocin motif, which is considered a main branching point in the lignin structure has been investigated. We have designed a protocol for the catalytic reductive cleavage of lignin model compounds representing this motif, in the presence of Pd/C and benign hydride donors. The cleavage of the dibenzodioxocin structure results in the formation of dimeric biaryl compounds. Unlike monomers, the valorization of lignin-derived dimers is less studied. The last chapter is focused on the transformation of biaryls into highly functionalized synthetic building blocks. This was achieved via a visible light induced dearomative spirolactonization of biaryl carboxylic acids. The synthetic value of the obtained products was demonstrated by the conversion of the products into more complex structures.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p