Diazotization of 6-amino-2-phenyl-7-chloro-2H-benzotriazole-4-carboxylic acid and transformations of the resulting diazo compounds

Abstract

6-Amino-2-phenyl-7-chloro-2H-benzotriazole-4-carboxylic acid was prepared by oxidation of 2,5-diamino-4-chloro-2-phenylazobenzoic acid, and its diazotization and subsequent transformations of the diazo compounds were studied. 7-Hydroxy-2-phenyl-2H-benzotriazole-4-carboxylic acid was prepared.The chemical properties of 2H-benzotriazoles containing several substituents in the benzene moiety are studied insufficiently [1, 2] because of limited availability of di-and trisubstituted m-phenylenediamines required for their preparation. In this connection, starting from 4-chloro-3,5-diaminobenzoic acid, we prepared by the known scheme [3] 6-amino-2-phenyl-7-chloro-2H-benzotriazole-4-carboxylic acid I and performed with it certain chemical transformations.Amino compound I is diazotized in HCl difficultly because of its poor solubility and low basicity of the amino group caused by the electron-withdrawing properties of the triazole moiety [4]. After prolonged standing at room temperature, the reaction mixture contains, according to TLC, the starting compound exhibiting strong blue luminescence. When the diazotization was performed with addition of acetic acid, in which compound I is readily soluble, the reaction was complete in 1 h. The resulting diazonium salt II entered into further transformations without complications only in acid solution: Its reaction with N,N-diethylaniline yielded azo compound III, and the reaction with a solution of SO 2 in acetic acid in the presence of HCl yielded benzotriazolesulfonyl chloride IV and 6,7-dichloro-2-phenyl-2H-benzotriazole-4-carboxylic acid V. At the same time, attempted azo coupling of diazonium salt II with 2-naphthol in alkaline solution failed because of tarring of the reaction mixture, probably caused by instability of II under these conditions.We believe that the specific features of the diazo compound obtained from I are confirmed by the results of diazotization in aqueous sulfuric acid at elevated temperature. The diazo compound isolated from the reaction was characterized by 1 H NMR, mass, and IR spectra, which indicate that the compound exists in the form of quinone diazide VI. This compound was also prepared by treatment of a solution of diazonium salt II in acetic acid with sodium carbonate. The presence in VI of the diazo function in the form of diazo rather than diazonium group is confirmed by a strong narrow band in the IR spectrum at 2180 cm !1 [537]. Formation of VI is apparently due to lability of the chlorine atom in the molecule of II; this atom is replaced by the hydroxy group under the action of water, which is followed by the tautomeric transformation into the diazonium salt of hydroxybenzotriazole. Diazo compound VI is highly stable, so that we detected a molecular ion in its mass spectrum.Quinone diazide VI is formed in a high yield and is stable in storage. It reacts with 2-naphthol in alkaline solution to form 2,2-diaryl hydroxy azo compound VII and undergoes nitrogen substitution in a strongly acidic or strongly alkaline solution, i.e., under the cond...