Determination of organic pharmaceuticals with N-bromosuccinimide. Part IV. Some pyrazolone derivatives by back-titration
A back-titration method is described for the determination of pyrazolone derivatives with N-bromosuccinimide. Under the experimental conditions used, 4 molar equivalents of N-bromosuccinimide are consumed by aminophenazone (amidopyrine; 2,3-dimethyl-4-dimethylamino-1-phenyl-3-pyrazolin-5-one), morazone [2,3-dimethyl-4-(3-methyl-2-phenylmorpholinomethyl)-1-phenyl-3-pyrazolin-5-one] and propyphenazone (4-isopropyl-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one). With phenazone (2,3-dimethyl-1-phenyl-3-pyrazolin-5-one) and dipyrone [sodium (2,3-dimethyl-5-oxo-1-phenyl-3-pyrazolin-4-yl)methylaminomethanesulphonate] 5 molar equivalents are consumed. A reaction mechanism involving quaternisation of the N-methyl group at the 2-position, followed by ring cleavage and bromination of the aromatic ring, is proposed; this was confirmed by nuclear magnetic resonance spectral analysis of the brominated phenazone.