Studies on L-Ascorbic Acid Derivatives. IV. The Ferric Chloride Reaction of L-Ascorbic Acid 3-Phosphate and Its Application for the Colorimetric Determination

Abstract

The wine red complex of iron (III)-L-ascorbic acid 3-phosphate was investigated spectrophotometrically. The color which showed a maximum absorption at 480 mμ was observed in aqueous solution over the acidity range from -2.0 (Ho) up to pH 5. The maximum intensity of the color was approximately at pH 0.9. Addition of an organic solvent prevented the coloration. The composition of the chelate was observed to be 1 : 1 in the molar ratio, L-ascorbic acid 3-phosphate/iron (III). Similarly, L-ascorbic acid 2-phosphate, 3-pyrophosphate, bis (L-ascorbic acid-3, 3') phosphate, L-ascorbic acid 2- and 3-phenylphosphates gave the corresponding iron (III)-chelates. Whereas, L-ascorbic acid 2- and 3-diphenylphosphate and L-ascorbic acid 3-sulfate gave no coloration. As a result of the test, acid stable colorations in the former group of compounds are probably due to the presence of the enolic group which can take part in the chelate formation with the vicinally located primary or secondary phosphoryl group. The coloration was applied to a colori metric method in the determination of L-ascorbic acid 3-phosphate.