Identification and determination of impurities in salicylanilide

In studies on the production of salicylanilide an assay method for salicylanilide itself and methods for the identification and determination of impurities were required. In addition to the starting materials (aniline and salicylic acid) four impurities were isolated and identified : salicylsalicylanilide, ar -phosphonosalicylanilide, 4-hydroxybenzanilide, and the p -hydroxybenzoate of 4-hydroxybenzanilide. Salicylanilide was assayed by direct ultraviolet spectrophotometry in basic methanol solution. Salicylic acid and phosphonosalicylanilide were extracted from a salicyl-anilide-chloroform solution with dilute sodium bicarbonate solution. Aniline and salicylsalicylanilide were determined by passing a methanolic solution of salicylanilide through Dowex 2, acetate-form, resin. Aniline, and methyl salicylate resulting from alcoholysis of salicylsalicylanilide, were contained in the eluate. All impurity concentrations were determined by ultraviolet spectrophotometry.