The Azure Dyes: Their Purification and Physicochemical Properties. I. Purification of Azure A

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Abstract
A method is described for the separation of azure A from commezcial samples of polychrome methylene blue. Up to 300 mg of the pure dye may be isolated in this way. The method is based on chromatography using columns 90 cm high, 7 cm in diameter, loaded with 3 g of polychrome methylene blue. The absorbent is silica gel, the eluent a mixture of acetic and formic acid. Poor solubility of the dye acetate in water necessitates dissociation of the acetate by alkalinization and subsequent conversion of the dye to the chloride with diluted Ha. Demethylation that occasionally occurs during this procedure is negligible. Pure azure A does not spontaneously demethylate under ordinary conditions.

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