5-Formylfuroic acid and the carbazole reaction for uronic acids and acidic polysaccharides

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Abstract
The absorption spectra in sulfuric acid, with and without carbazole, of 5-formylfuroic acid, 2,5-diformylfuran, furfuraldehyde, 5-hydroxymethylfurfuraldehyde, furan-2,5-dicarboxylic acid and the uronic acids indicate that 5-formylfuroic acid is responsible for color formation in the carbazole procedures for estimating uronic acids. 5-Formylfuroic acid appears to be the principal material absorbing UV light formed under the conditions examined. 2,5-Diformylfuran also gives a color, with a different absorption spectrum, under the same conditions. Glucuronic acid in oxidized cellulose and heparin gives 5-formylfuroic acid more rapidly than the uncombined material.