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Infrared Absorption Similarities between Hymatomelanic Acid and Methylated Humic Acid¹

ABSTRACT

Infrared analysis was conducted comparing hymatomelanic acid and methylated humic acid extracted from two Ultisols and one Inceptisol. The results revealed close similarities in spectrograms, leading to the assumption that hymatomelanic acid was not an artifact, but a naturally esterified or methylated fraction of the humic molecule liberated by ethanol extraction. Carbon-14-labeled ethanol extraction of humic acid yielding hymatomelanic acid showing radioactivity counts below the control supported the assumption for the natural occurrence of hymatomelanic acid. Methylation of humic and hymatomelanic acids increased the infrared absorption between 3000 to 2800 and at 1720, 1460, and 1400 cm^-1, for C-H, carbonyl, CC-H₃, and carboxyl stretching vibrations, respectively. Separation of the ester group from the hymatomelanic acid molecule by dissolution with 2N NaOH and HCl eliminated its blocking effect on the carboxyl vibration in COO^- form and the absorption at 1620 cm^-1 regained in intensity.

¹ Contribution of the Univ. of Georgia, College of Agr. Exp. Sta., Athens, Ga.

² Associate Professor, Univ. of Georgia, Athens, 30602.

Received for publication September 30, 1974. Accepted for publication October 15, 1974.