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

The degradation of the lignin model compounds guaiacylglycerol beta -guaiac yl 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 c leavage of beta -ether bonds had occurred. No acidolysis products (e.g. "Hi bbert ketones") were detected in the reaction mixtures obtained when the mo dels 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) t hat may be formed via a homolytic cleavage of the beta -ether bond were det ected in the reaction product of syringylglycerol beta -syringyl ether. Onl y homolysis products were detected in the reaction mixture obtained on heat ing (175 degreesC) of guaiacylglycerol beta -guaiacyl ether in buffered (pH 3) water-ethanol (3:1) solution. Bisulfite cooking of guaiacylglycerol bet a -guaiacyl ether gave only sulfonated starting material and no sulfonic ac ids derived from coniferyl alcohol were formed.