Abstract
Colorimetric determination of aminopyrine in mixed anti-cold pharmaceutical preparations was studied, and a highly selective and precise method has been established. The mechanism of color development was found to be due to the oxidative condensation of 4-aminoantipyrine produced from aminopyrine by oxidative demethylation with phenol in a weak alkaline medium yielding an indophenol type pigment. Optimum conditions for color development were investigated thoroughly, and the different effects in various buffer solutions on the color development have also been studied. N-Methylaminoantipyrine produced by the dissociation of sulpyrine gave the same coloration as aminopyrine, but the interference of N-methylaminoantipyrine could be eliminated by its acetylation. Conditions of the acetylation were also discussed. The acetylation gave satisfactory result both in aqueous medium and in chloroform.
