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Characterization and diagenesis of strong-acid carboxyl groups in humic substances

Applied Geochemistry

By:
, , ,
DOI: 10.1016/S0883-2927(02)00100-2

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Abstract

A small fraction of carboxylic acid functional groups in humic substances are exceptionally acidic with pKa values as low as 0.5. A review of acid-group theory eliminated most models and explanations for these exceptionally acidic carboxyl groups. These acidic carboxyl groups in Suwannee River fulvic acid were enriched by a 2-stage fractionation process and the fractions were characterized by elemental, molecular-weight, and titrimetric analyses, and by infrared and 13C- and 1H-nuclear magnetic resonance spectrometry. An average structural model of the most acidic fraction derived from the characterization data indicated a high density of carboxyl groups clustered on oxygen-heterocycle alicyclic rings. Intramolecular H-bonding between adjacent carboxyl groups in these ring structures enhanced stabilization of the carboxylate anion which results in low pKa1 values. The standard, tetrahydrofuran tetracarboxylic acid, was shown to have similar acidity characteristics to the highly acidic fulvic acid fraction. The end products of 3 known diagenetic pathways for the formation of humic substances were shown to result in carboxyl groups clustered on oxygen-heterocycle alicyclic rings.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Characterization and diagenesis of strong-acid carboxyl groups in humic substances
Series title:
Applied Geochemistry
DOI:
10.1016/S0883-2927(02)00100-2
Volume
18
Issue:
3
Year Published:
2003
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
471
Last page:
482
Number of Pages:
12