Permanganate oxidation of lignin

Tsutsumi Y, Islam A, Anderson CD, Sarkanen KV (1990) Acidic permanganate oxidations of lignin and model compounds comparison with ozonolysis Holzforschung 44 59-66... 

Evidence for the occurrence of a series of additional types of lignin units (for instance 60-64) have been obtained in studies of degradation products obtained on permanganate oxidation of lignins [4], On the basis of the yields of oxidation products, Adler [4] concluded that only small amounts of units such as 60-64 can be present in lignins. 

Fig.6.3.2. Major carboxylic acid methyl esters formed in the oxidation of lignin with potassium permanganate (Compounds 3, 6 and 9 are from hardwood lignin)...

Biphenyl coupling occurs to some extent on cupric oxide oxidation of lignin model compounds [55,56]. This indicates that the value derived from permanganate oxidation studies is slightly too high. On the basis C NMR examinations, Drumond et al. [57] arrived at a higher value for the frequency of biphenyl units (24-26%). The accuracy of this estimate can be questioned, since no separate signals from biphenyl units can be discerned in the spectra. 

Lopes M., Neto C.P., Evtuguin D., Silvestre A.J.D., Gil A., Cordeiro N., Gandini A., Products of the permanganate oxidation of cork, desuberized cork, suberin and lignin from Quercus suberh., Holtforschung, 52(2), 1998, 146-148. 

Fig. 4-1. Examples of classical methods indicating a phenylpropanoid structure of lignin. (A) Permanganate oxidation (methylated spruce lignin) affords veratric acid (3,4-dimethoxybenzoic acid) (1) in a yield of 8% and minor amounts of isohemipinic (4,5-dimethoxyisophtalic acid) (2) and dehydrodiveratric (3) acids. The formation of isohemipinic acid supports the occurrence of condensed structures (e.g., /3-5 or y-5). (B) Nitrobenzene oxidation of softwoods in alkali results in the formation of vanillin (4-hydroxy-3-methoxybenzaldehyde) (4) (about 25% of lignin). Oxidation of hardwoods and grasses results, respectively, in syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde) (5) and p-hydroxybenzaldehyde (6). (C) Hydrogenolysis yields pro-pylcyclohexane derivatives (7). (D) Ethanolysis yields so-called Hibbert ketones (8,9,10, and 11).

Fig.6.3.1. Reaction sequence for the oxidative degradation of lignin with potassium permanganate...

Additional evidence for the stereospecific conversion of fi-O-4 and arylglycerol lignin models to tetronic acids under conditions that selectively oxidize aryl rings also comes from acidic permanganate oxidation (Tsutsumi et al. 1990). This method gives essentially the same products as ozonation. 

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