Oxidation of Lignin Model Compounds Using Single-Electron-Transfer Catalysts

Article abstract of DOI:10.1021/jo00243a014

The single-electron-transfer oxidation of model compounds representative of the arylglycerol β-aryl ether and 1,2-diarylpropane linkages of lignin has been examined by using Co(II), Mn(II), or Co(II)/Mn(II) as catalysts.Catalytic oxidation of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (DMMP) in 80percent acetic acid with 500 psi of 4percent oxygen in nitrogen and at 170 deg C resulted predominantly in products of C_α-C_β bond cleavage when using Co(II)/Mn(II) as catalyst.C_α-C_β bond cleavage of DMMP results from an initial single-electron oxidation toproduce an intermediate aromatic radical cation; in the absence of oxygen and catalyst, acid-catalyzed β-aryl ether cleavage was the predominant reaction pathway.Dihydroanisoin (DHA) and 1,2-bis(4-methoxyphenyl)propane-1,3-diol (BMPD) were oxidized by stoichiometric quantities of Co(III) to give solely products of C_α-C_β bond cleavage but produced only acid-catalyzed dehydration products under reaction conditions necessary for catalytic oxidation.The application of this oxidation reaction as a replacement for chlorine bleaching of paper pulp is discussed.