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You are here: HomeGroupsC3Bio Entire GroupResourcesPublicationsCatalytic oxidation of para-substituted phenols with cobalt–Schiff base complexes/O2—selective conversion of syringyl and guaiacyl lignin models to benzoquinonesAbout

Catalytic oxidation of para-substituted phenols with cobalt–Schiff base complexes/O2—selective conversion of syringyl and guaiacyl lignin models to benzoquinones

By Diana Cedeno1, Joseph J Bozell1

1. University of Tennessee

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Abstract

Models of guaiacyl (G) and syringyl (S) subunits in lignin have been catalytically oxidized to their corresponding p-quinones in the presence of molecular oxygen. The oxidation of syringyl-like phenols readily occurred with 5-coordinate cobalt catalysts on which one of the ligands is a monodentate pyridine or imidazole base that coordinates axially to the metal. Formation of p-quinones with this system depends on the coordination of the axial base to the metal as influenced by its pKa and its size. The yield of p-quinones from guaiacyl models was markedly improved by the addition of a sterically hindered aliphatic nitrogen base that does not coordinate to the catalyst. A mechanism involving deprotonation of the phenol substrate by the bulky base is proposed.
2012 Elsevier Ltd. All rights reserved.

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