SYNTHESIS OF 2, 6-DIAMINO-3-PHENYLAZOPYRIDINE-1-OXIDE AND ITS HYDRO- CHLORIDE

The compound 2, 6-diamino-3-phenylazopyridine hydrochloride salt is a genito-urinary antiseptic drug under the trade name Pyridinium. This study is directed towards the occurrence of an oxidation reaction to convert the tertiary amine present in 2, 6-diamino-3- phenylazopyridine hydrochloride to form an N-oxide derivative as an impurity in the process for its preparation. This was done by the independent synthesis of 2, 6-diamino-3-phenylazopyridine-1-oxide hydrochloride salt by two independent routes. The presence of three amine functions in the molecule required first to protect the primary amine groups by derivatisation so that oxidation occurs exclusively at the tertiary amino group of the pyridine ring. 2, 6-diamino-3-phenylazopyridine was acetylated to get 2, 6- diacetamido-3-phenylazopyridine whose structure was confirmed from 1 H NMR and mass spectral data. The oxidation of diacetyl derivative with peracetic acid resulted not only in the N-oxide formation but also in the cleavage of one of the acetamido group to give 2(6)-acetamido-6(2)amino-3- phenylazopyridine-1-oxide. The alkaline hydrolysis of the N-oxide form gave 2, 6-diamino-3-phenylazopyridine-1-oxide which on treatment with hydrochloric acid gave 2, 6-diamino-3-phenylazopyridine-1-oxide hydrochloride. In yet another route the N-oxide was prepared by the coupling reaction between benzene diazonium chloride and 2, 6-diaminopyridine-1- oxide in aqueous hydrochloric acid medium. This reaction resulted in the formation of 2, 6-diamino-3- phenylazopyridine-1-oxide hydrochloride as an insoluble salt. The structure of the N-oxide was confirmed from 1 H NMR and mass spectral data. A co-injection HPLC analysis showed the complete absence of 2, 6-diamino-3-phenylazopyridine-1-oxide hydrochloride in 2, 6- diamino-3-phenylazopyridine hydrochloride in its manufacturing process. INTRODUCTION: The pharmacologically active compound namely 2, 6-diamino-3-phenylazo- pyridine hydrochloride 1 (PPHCl) is the active ingredient of the genito-urinary antiseptic drug 2