THERMAL-REACTIONS OF THE BONDS IN LIGNIN .4. THERMOLYSIS OF DIMETHOXYPHENOLS

Thermolysis of 3,5-, 2,3- and 2,6-dimethoxyphenols possessing the characteristic aromatic methoxyl group typical of lignins have been studied. The experiments were carried out at reaction temperatures 523 to 598 K and for reaction times ranging from 2 to 6 h. 2,3-Dimethoxyphenol is manyfold more reactive than the other two isomers, while, 2,6-dimethoxyphenol is only slightly more reactive than, 3,5-dimethoxyphenol. The methoxyl groups in 2,3- and 2,6-dimethoxyphenols exert steric and electronic effects, while those in 3,5-dimethoxyphenol contribute largely to electronic effects. Certain reactions are well pronounced in all dimethoxyphenols, while others become less significant in the individual dimethoxyphenols. The major reaction pathways common to all three dimethoxyphenols are the cleavage of the alkyl C-O bond to form the corresponding dihydroxyanisoles and ring methylation to form the corresponding dimethoxymethylphenols. The cleavage of the aromatic C-O bond to form two-oxygen atom products is significant for 2,6-dimethoxyphenol. 3,5-Dimethoxyphenol forms more ring methylated products than either 2,3- or 2,6-dimethoxyphenol.