Repeating Units in Spruce Lignin

The prevailing opinion today is that lignin is a statistical polymer for which no structural formula in the true sense can be presented but only a structural scheme of the type proposed by Adler and Freudenberg. Careful fractionation of the lignosulfonates and other compounds that are dissolved in the liquor in a sulfite cook shows, however, that the lignosulfonic acids may not be derived from a statistical polymer but from an ordered polymer composed of repeating units, and that sprucewood contains appreciable amounts of aromatic compounds which are related to true lignin as hemicellulose is to cellulose. We believe that it is necessary in lignin studies to be sure that the lignin preparation studied does not contain any of these hemilignin components. We have studied the properties of spruce lignin by first dissolving the lignin and hemilignin from the wood by sulfite cooking liquors of varying composition under different experimental