Erythro/threo ratio of β-O-4 structures as an important structural characteristic of lignin. I: Improvement of ozonation method for the quantitative analysis of lignin side-chain structure

Abstract

Ozonation as a quantitative tool to analyze the stereo structures of arylglycerol-β-aryl ether linkages was examined using wood meal, milled wood lignin, and a lignin model compound, 1-(3,4-dimethoxyphenyl)-2-(2- methoxyphenoxy)-1,3-propanediol (veratrylglycerol-β-guaiacyl ether, VG). The procedure was improved. When mild postreduction was conducted for ozonation products, the total yield of erythronic and threonic acids from this model compound was 74%, which is 15% higher than the yield without postreduction. A decrease in the recovery of these two acids under prolonged ozonation treatment was successfully suppressed by postreduction. The erythro/threo ratio of VG determined by the ozonation method with postreduction is in good agreement with the ratio determined by 1H-nuclear magnetic resonance. Excellent reproducibility of the yield was obtained by adopting a procedure that included trimethylsilylation of ammonium salts of ozonation products using a dimethylsulfoxide-hexamethyldisilazane-trimethylchlorosilane mixture and subjecting it to gas chromatography analysis. It was concluded that arylglycerol-β-aryl ether structures comprise at least 35% of the C 3-C6 structure in birch wood meal, with an erythro/threo ratio of 2.8.