Trapping of p-coumaryl and coniferyl alcohol during soda-anthraquinone treatment: a means of estimating uncondensed β-O-4 structures in native lignin.

In most native lignins, at least 50% of the phenylpropane (C(9)) units are involved in β-O-4 linkages. It was recently observed that ethylguaiacol (EG) was efficient at trapping coniferyl alcohol generated from the cleavage of uncondensed β-O-4 dimeric structures during soda-anthraquinone (AQ) or SAQ delignification of sugar maple wood meal. Some of the coniferyl alcohol was transformed to vinylguaiacol and isoeugenol, and the α-carbon atom in all three monomers formed C-C bonds with the C-5 position of EG. In the present research, eucalyptus and sugar cane bagasse meals were also investigated, and the yields of uncondensed β-O-4 structures in the nonsyringyl fraction were quantitated. The estimates of the uncondensed fraction of the lignin in the three samples (assuming S units are 90-95% uncondensed) were in close agreement with results from traditional but more tedious methods such as permanganate oxidation or spectroscopic methods requiring a sample representative of native lignin.