Structural Analysis of Humic Materials

Abstract

classical method for structure determination in complex molecules is
to degrade the molecule into smaller recognisable fragments. This approach has
been applied in the past to humic/coal type analysis but frequently using such
powerful reagents that there has been some doubt about the relationship of the very simple degradation products to the original materials. The evidence so far available indicates that in humic acids the units are held together not only by covalent bonding but also by a substantial network of hydrogen bonds, it is thought that it is these secondary interactions which are mainly responsible for the intractability and insolubility of these materials. The purpose of this investigation was to develop milder and more specific methods for the structural degradation of humic acids. The main thrust of the work was towards minimising hydrogen bonding interactions.

The particular approaches used were:
(i) Protection of -OH groups. This is a common method for removal of
hydrogen bonding interactions. However in these heterogeneous systems it
has not been possible so far to obtain quantitative protection. We tried to
achieve this by using phase transfer procedures.

(ii) | Removal of -OH and >C=O functions. The removal of -OH and >C=O
functions not only reduces hydrogen bonding but also the number of active
sites. The C-H groups adjacent to> C=O are highly susceptible to oxidative
attack and subsequently C-C cleavage occurs at these sites. If -OH and
>C=O groups are removed the number of sites for oxidative attack is
reduced and the selectivity of the oxidation process increased. Substantial
progress was made in converting humic acids to their hydrocarbon-like
backbone structure lacking -OH and sC=O groups.

Using a combination of the above methods produces materials
sufficiently soluble in organic solvents for analysis by nmr and sufficiently volatile
for study in the gc/ms system.

Date of Award	1986
Original language	English