Characterization of peatified and coalified wood by tetramethylammonium hydroxide (TMAH) thermochemolysis

Seven samples of peatified and coalified wood, varying in rank from peat to subbituminous coal, have been analyzed using a new technique: thermochemolysis with tetramethylammonium hydroxide (TMAH). The preserved lignin in the coal undergoes thermochemolysis reactions when subjected to treatment with TMAH at 300 degrees C for 10 min, yielding a series of methylated guaiacyl derivatives that originate from the cleavage of beta-O-4 bonds from preserved lignin. As rank increases from peat to subbituminous coal, the yields of lignin-derived monomers decreases and the ratio of methylated acids to methylated aldehydes increases systematically, describing a general increase in the level of alteration of the lignin side chain. This new technique of TMAH thermochemolysis lends itself well to studies of structural changes that may occur in lignin as it is being altered during coalification. Data obtained in this study along with structural models proposed in the past have given insight to mechanistic changes that occur in the lignin biopolymer during early coalification. We propose that the first reaction to occur is beta-O-4 bond cleavage and subsequent re-alkylation of the aromatic ring, followed by demethylation of the methoxyl side chain functionalities to produce catechol-like structures.