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Use of some heterocyclic azo dyes as analytical reagents. I. Preparation of azo dyes and spectrophotometric investigation of (7-oxo-5,5-dimethyl-4,5,6,7-tetrahydro-2-benzothiazolylazo)phenols and (7-oxo-5,5-dimethyl-4,5,6,7-tetrahydro-2-benzothiazolylazo) resorcinoes

E. Kuchár

Institut für analytische Chemie der Naturwissenschaftlichen Fakultät an der Komenský-Universität, Bratislava 1


Abstract: Heterocyclic azo dyes with a characteristic group of donor atoms were prepared by diazotization of 2-amino-7-keto-5,5-dimethyl-4,5,6,7-tetrahydrobenzothiazole followed by coupling with the proper phenols. These substances form with some cations chelates characteristic in colour. The estimated sensitivity of reactions of 2-(7-keto-5,5-dimethyl-4,5,6,7-tetrahydrobenzothiazolylazo) -2,4-dihydmxyphenyl and 2-(7-keto-5,5-dimethyl- -4,5,6,7-tetrahydrobenzothiazolylazo)-6-methyl-2,4-dihydroxyphenyl with metal ions attain high pZ) values. 2-(7-Keto-5,5-dimethyl-4,5,6,7-tetrahydrobenzothiazolylazo)- 4-hydroxyphenyl exhibits in 20% aqueous ethanol solutions distinctly coloured acidobasic forms RH2+, RH, R- with absorption maxima at λ 500, 430 and 580 nm. 2-(7-Keto-5,5-dimethyl-4,5,6,7-tetrahydrobenzothiazolylazo)- 2,4-dihydroxyphenyl exists in 20% aqueous ethanol solutions at pH 0—12.5 as RH3+ , RH2, RH- , R2-  with absorption maxima at λ 525, 480, 530 and 545 nm. Molar absorptivities and ionization constants of the particular acidobasic forms were determined by graphic and logarithmic analysis of the pH curves.

Full paper in Portable Document Format: 241a28.pdf (in German)


Chemical Papers 24 (1) 28–37 (1970)

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