The structure of lignins in pulps

Summary

Several important parameters pertaining to the recovery, separation, quantitative identification, and yield correction of permanganate oxidation products from lignins were critically evaluated. The “routine recovery” procedure was amended by a series of “exceptional recovery” operations which permitted retrieval of a maximum of 157 mg of degradation products from 100 mg lignin. The “exceptional fractions” contained more low molecular weight compounds than the routinely isolated fraction, calling for the employment of molecular weight distribution data of degradation product mixtures in combination with data by gas chromatography for interpretation in terms of structural features. Approximately 1/5 to 1/3 of the degradation products had molecular weights in excess of dimeric fragments.

Separation and quantitative identification by gas chromatography was reproducible within 1.5 and 3.5%, respectively. Adjustment of experimental yields for yield losses encountered during degradation and separation was best accomplished by the use of a correction factor for the degradation of aromatic ring substituents as advocated by Larsson and Miksche, along with molecular weight distribution data. This method, however, slightly overestimates degradation products with more than one carboxy group per aromatic ring in favor of those with fewer than one.