Estimation of the Aromatic Units in Lignin by Nucleus Exchange - A Reassessment of the Method

Abstract

A series of lignin model compounds was subjected to the nucleus exchange reaction (boron trifluoride-phenol at 180°C) to evaluate the application of the procedure to the study of wood and pulp lignin structure. The nucleus exchange reaction of the series of compounds gave rise to catechol in a range of yields, and in every case no starting material remained. In contrast to earlier reports, lignin model diphenyl ether and biphenyl compounds also gave rise to catechol. On the basis of these results and application of the nucleus exchange reaction to woodmeals and kraft pulps, we conclude that the nucleus exchange reaction does not allow accurate measurement of aromatic units in lignin.