Oxidative cleavage of C-C bonds in lignin.

Lignin is an aromatic polymer that constitutes up to 30 wt% of woody biomass and is considered the largest source of renewable aromatics. Valorization of the lignin stream is pivotal for making biorefining sustainable. Monomeric units in lignin are bound via C-O and C-C bonds. The majority of existing methods for the production of valuable compounds from lignin are based on the depolymerization of lignin via cleavage of relatively labile C-O bonds within lignin structure, which leads to yields of only 36-40 wt%. The remaining fraction (60 wt%) is a complex mixture of high-molecular-weight lignin, generally left unvalorized. Here we present a method to produce additional valuable monomers from the high-molecular-weight lignin fraction through oxidative C-C bond cleavage. This oxidation reaction proceeds with a high selectivity to give 2,6-dimethoxybenzoquinone (DMBQ) from high-molecular-weight lignin in 18 wt% yield, thus increasing the yield of monomers by 32%. This is an important step to make biorefining competitive with petroleum-based refineries.

Continuous-Flow Synthesis of Supported Magnetic Iron Oxide Nanoparticles for Efficient Isoeugenol Conversion into Vanillin.

This work presents the synthesis of iron oxide nanocatalysts supported on mesoporous Al-SBA-15 by using a continuous-flow setup. The magnetic nanomaterials were tested as catalysts in the oxidative disruption of isoeugenol by using hydrogen peroxide as a green oxidant, featuring high activities (63-88 % conversion) and good selectivities to vanillin (44-68 %). The catalytic systems exhibited good magnetic properties when synthesized under continuous-flow conditions at temperatures not exceeding 190 °C. The use of microwave irradiation significantly reduced times of reaction drastically but exerted negative effects on catalyst reusability.