Fe(TSPc)-catalysed benzylic oxidation and subsequent dealkylation of a non-phenolic lignin model

The mechanism by which the phthalocyanine complex trisodium tetra-C sulfona tophthalocyanineiron(III) (Fe(TSPc)) promotes oxidation and dealkylation of non-phenolic benzyl alcohol units in lignin under alkaline conditions was investigated using simple lignin model compounds. The iron complex effectiv ely oxidised benzylic hydroxyl groups in 2-hydroxyethyl apocynol (5), with the extent of oxidation increasing with the amount of Fe(TSPc) added. To a limited extent, Fe(TSPc) also catalysed the oxidation of 5 by small amounts of oxygen in the reaction mixture. However, the extent of oxidation did no t increase on adding excess air or oxygen, as greater amounts of oxygen als o increased complex degradation. Phenolic products were formed in these rea ctions in the presence of Fe(TSPc), but at a rate slower than that of the b enzylic oxidation. Further experiments indicated that the phenolic products were formed by base-promoted loss of the ether group at C4 and that such d ealkylation occurred more readily in oxidised products.