The “Catalytic” Effect of Anthrone and Anthrahydroquinone in Cleaving β-Aryl Ether Bonds in Lignin Model Compounds

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Abstract
To elucidate the mechanism of anthrone-promoted β -ether cleavage reactions, the phenolic lignin model compound 1, 1-(4-hy-droxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol, was heated with 0.1 mole of anthrone (AN) or anthrahydroquinone (AHQ) at 140 °C for 1/2, 1, 2, 3 and 5 hours in 1 M sodium hydroxide solution. The cleavage products [2-methoxyphenol and (2-meth-oxy-4-propenyl)phenol] were the same as in experiments with equimolar amounts or excess of AN and the yields increased as a function of reaction time to a maximum corresponding to the cleavage of four to five moles of 1 per one mole of AN. AHQ was found to react in a similar manner. This “catalytic” effect is tentatively attributed to sequential transformations of AN and AHQ to products capable of causing further reductive cleavages. GC-MS analysis of the reaction mixture showed the presence of by-products which indicate that some catalyst regeneration through oxidation of 1 or its hydrolysis products may have occured. 1-Hydroxyanthrone had a similar “catalytic” effect in cleaving β-ether bonds, but glucose did not.