REACTIONS OF METAL-ION COMPLEXES WITH LIGNIN MODEL COMPOUNDS .1. CO(TSPP) AS A SINGLE-ELECTRON TRANSFER CATALYST AND IMPLICATIONS FOR THE MECHANISM OF AQ PULPING

Cleavage of the beta-aryl ether bonds of the lignin model compounds gu aiacylglycol beta-guaiacyl ether (1) and guaiacylglycerol beta-guaiacy l ether (11) to form guaiacol was found to be catalyzed by the water s oluble porphyrin complex trisodium meso-tetra-4-sulfonatophenylporphin ecobalt(III), (Co(TSPP)). The resulting product distributions were rem arkably similar to those obtained for the anthraquinone (AQ) catalyzed reactions under the same conditions. Studies of the reactions of Co(T SPP) with proposed intermediate compounds indicate that the major rout e to guaiacol formation involves reaction of the reduced catalyst, Co( II)(TSPP), with the quinone methides 9 and 13 which are derived from t he 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 propo sal for the AQ catalyzed reactions of 1 are discussed.