Practical Methods for Purification of Anionic Dyes as Their Sodium, Potassium and Lithium Salts

Anionic dyestuffs having high purity can be obtained employing standard recrystsllization techniques. The dye may be obtained as the sodium, potassium or lithium salt. The free acid form of the dye is dissolved in butanol. Impurities are removed during partition with water. The metal salt of the dye is obtained by adding the appropriate alkali. Alter natively, dimethyl formamide (DMF) is employed to extract the dye from the ionic impurities. The sodium salt of the dye is recovered. The free acid may be obtained using DMF-acid extraction followed by conversion to the desired metal salt with alkali. The purification and characterization of four direct dyes (C. I. Direct Red 2, C. I. Direct Yellow 12, C. I. Direct Blue 78, C. I. Direct Green 26) and two acid dyes (C. I. Acid Red 85, C. I. Acid Blue 78) is described.