Cleavage of arylglycerol beta-aryl others under neutral and acid conditions

The degradation of the lignin model compounds guaiacylglycerol beta -guaiacyl ether, syringylglycerol beta -syringyl ether and syringylglycerol beta -guaiacyl ether in acid and neutral aqueous solutions was studied. Analysis of the reaction products of the model compounds obtained on heating with 0.2 M acetic acid at 160 degreesC showed that both homolytic and acidolytic cleavage of beta -ether bonds had occurred. No acidolysis products (e.g. Hibbert ketones) were detected in the reaction mixtures obtained when the models were heated with water alone. Heating of the models in dilute sulfuric acid resulted in acidolytic cleavage of beta -ether bonds; two compounds (sinapaldehyde and a condensation product of sinapyl alcohol and syringol) that may be formed via a homolytic cleavage of the beta -ether bond were detected in the reaction product of syringylglycerol beta -syringyl ether. Only homolysis products were detected in the reaction mixture obtained on heating (175 degreesC) of guaiacylglycerol beta -guaiacyl ether in buffered (pH 3) water-ethanol (3:1) solution. Bisulfite cooking of guaiacylglycerol beta -guaiacyl ether gave only sulfonated starting material and no sulfonic acids derived from coniferyl alcohol were formed.