Reactions of Metal Ion Complexes with Lignin Model Compounds Part I. Co(TSPP) as a Single Electron Transfer Catalyst and Implications for the Mechanism of AQ Pulping

Abstract

Abstract Cleavage of the β-aryl ether bonds of the lignin model compounds guaiacylglycol β-guaiacyl ether (1) and guaiacylglycerol β-guaiacyl ether (11) to form guaiacol was found to be catalyzed by the water soluble porphyrin complex trisodium meso-tetra-4-sulfonatophenvlporphinecobalt(III), (Co(TSPP)). The resulting product distributions were remarkably similar to those obtained for the anthraquinone (AQ) catalyzed reactions under the same conditions. Studies of the reactions of CofTSPP) with proposed intermediate compounds indicate that the major route to guaiacol formation involves reaction of the reduced catalyst, CoII(TSPP), with the quinone methides 9 and 13 which are derived from the phenolic model compounds 1 and 11 respectively. It is proposed that the mechanisms of these reactions involve single electron transfer to the quinone methide as the first step. The implications of this proposal for the AQ catalyzed reactions of 1 are discussed.