REDUCTIVE SPLITTING OF HUMIC SUBSTANCES WITH DRY HYDROGEN IODIDE

The procedure of mild hydrogen iodide for reductive splitting, develop ed earlier for selective splitting of etheric bonds in lignin and lign in-carbohydrate complex, has been applied successfully to the depolyme rization of humic and fulvic acids of both soil and aquatic origin. Mo lecular mass distribution patterns analyzed by gel-permeation chromato graphy showed that the aromatic products were similar to lignins excep t for the absence of monomeric products. The oligomeric units can be t reated as branching points from lignin where phenyl-propane units are connected mainly by non-broken carbon-carbon bonds. Such homopolymer s egments are slowly degraded during humification processes and can play a role in the overall structure of humic substances: These lignin-der ived fragments comprise the major part of aromatic structures in humic substances. The experiments support the idea of the preservation of l ignin structural features during humification. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.