Structural Arrangement of Functional Groups in Soil Humic Acid as Revealed by Infrared Analyses
1965
Wagner, G. H. | Stevenson, F. J.
Humic acid from a brunizem soil was subjected to a series of treatments (methylation, saponification, acetylation) to determine the number and arrangement of functional groups when analyzed by a combination of chemical and infrared techniques. One-third of the COOH groups (total COOH, 390 meq/100 g) occurred in positions close enough to form cyclic anhydrides; two-thirds of the OH groups (total OH, 290 meq/100 g) were phenolic. Some phenolic OH groups in the samples failed to methylate wth diazomethane. Potassium bromide catalyzed the formation of cyclic anhydrides by mild thermal treatment of acid-treated and methylated-saponified humic acids, but not of untreated humic acid. Acetylation gave a small amount of brown material (acetyl content, 20%) whose infrared pattern was characteristic of an acetylated carbohydrate. Tests for quinone and H-bonded phenolic OH groups were negative.
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