Phenols dimerization

This paper examines the nature and amounts of monomeric and dimeric phenolic constituents of the walls of graminaceous plants and the relationships of these constituents to wall biodegradability. 

Dimeric Phenolic Acid Constituents (Substituted Cyclobutanes) of Cell Walls... 

Figure 2 shows a difference curve obtained from methylol kraft lignin when untreated lignin was used as reference. The difference curve has a distinct maximum at 590 m/z, characteristic of the phenol alcohol structures formed. By comparing the absorbance at 590 m/z with the molar absorbance (e) of models investigated, the amount of phenol alcohols in lignin can be estimated. The numerical values depend somewhat on the e value of the model chosen. In this study a value of e = 840 was used, the increase found at 590 m/z between the molar absorbances of the dimeric phenol alcohol and its parent phenol of model II. 

Distillation from a brush-type molecular still separated the isolated lignins into three fractions containing alkyl-substituted monomeric phenols in the most volatile fraction, a mixture of monomeric phenolic alcohols and alkyl-substituted dimeric phenols in the intermediate fraction, and nonvolatiles which presumably contained dimeric phenolic alcohols and higher molecular weight material. Unfortunately, separation of monomeric alcohols and alkyl-sbustituted dimers was not complete, and this greatly hampered separation of the alkyl-substituted dimers in later chromatographic separations. 

Tri-O-methylellagic acid (dimeric phenolic lactone) PotentiUa candicans (Rosaceae) [root] AR (rat lens) (> 10)... 

Phenoxyl radicals are converted to quinones and products of phenol dimerization. Phenol oxidizes in water giving pyrocatechol and hydroquinone in the presence of metal ions [242], The best yields were obtained with Cu2+ and Fe3+ ions (100—150° C). 

The principal reaction of these compounds is dimerization ( phenol coupling ) to produce new C-C or C-O bonded hydroxylated biphenyls or hydroxydiphenyl ethers. These reactions have been observed in a wide variety of environmental and biological media (Taylor and Battersby, 1967). 

Nawwar MAM, Buddrus J, Bauer H 1982 Dimeric phenolic constituents from the roots of Tamarix nilotica. Phytochemistry 21 1755-1758... 

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