Electrochemical Conversion of the Lignin Model Veratryl Alcohol to Veratryl Aldehyde Using Manganese(III)-Schiff Base Homogeneous Catalysts
oleh: Lara Rouco, M. Isabel Fernández-García, Ana M. González-Noya, Gustavo González-Riopedre, Alexei M. Tyryshkin, Marcelino Maneiro
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2019-08-01 |
Deskripsi
Lignin and other colored structures need to be bleached after the Kraft process in the pulp industry. Development of environmentally-safe bleaching catalysts or electrocatalysts constitutes an attractive strategy for selective removal of lignin. Seven manganese(III)-complexes with Schiff base ligands <b>1−7</b> were synthetized and characterized by different analytical and spectroscopic techniques. The tetragonally elongated octahedral geometry for the manganese coordination sphere and the global µ-aquo dimeric structure were revealed by X-ray diffraction (XRD) studies for <b>1</b>, Mn<sub>2</sub>L<sup>1</sup><sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>(N(CN)<sub>2</sub>)<sub>2</sub> (N(CN)<sub>2</sub> = dicyanamide). Complexes <b>1−4</b> behave as more efficient peroxidase mimics as compared to <b>5−7</b>. Electrochemical oxidation of the lignin model veratrylalcohol (VA) to veratrylaldehyde (VAH) is efficiently catalyzed by a type of dimanganese(III) complexes in a chlorine-free medium. The electrocatalytic reaction proceeds through the oxidation of chloride into hypochlorite at alkaline pH along with the formation of hydrogen from water as a subproduct.