Temperature dependent absorption spectroscopy of some tautomeric azo dyes and Schiff bases

Fadhil S. Kamounah, Hem Joshi, Gert van der Zwan , Cees Gooijer, Liudmil Antonov

Publikation: Bidrag til tidsskriftTidsskriftartikelpeer review

Abstract

The spectral properties of several aromatic azo dyes of fundamental importance (4-phenylazo-1-naphthol, 1-phenylazo-2-naphthol and 2-phenylazo-1-naphthol) and Schiff bases (N-(2-hydroxy-1-naphthylmethylidene)aniline and N-(1-hydroxy-2-naphthylmethylidene)aniline) are investigated at temperatures down to 100 K. The observed spectral changes are interpreted in terms of the existing tautomeric equilibrium and hydrogen-bonding (H-bonding) with the solvent. In non-polar solvents the decrease in temperature leads, in all compounds except 4-phenylazo-1-naphthol, to a full transformation of the enol tautomeric form (A) to the quinone form (H). The temperature dependence of the equilibrium A [right left harpoons] H exhibits a shift around 240 K. In ethanol, due to intermolecular H-bonding, in the case of the azo dyes full transformation was not observed, while the behavior of the Schiff bases is the same as in non-polar solvents. The thermodynamic parameters of the equilibrium A [right left harpoons] H were estimated in both non-polar solvent and ethanol for all investigated compounds.
OriginalsprogEngelsk
TidsskriftRoyal Chemical Society. Journal. Perkin Transactions 2
Vol/bind12
Sider (fra-til)2303-2308
Antal sider6
ISSN1472-779X
DOI
StatusUdgivet - 2001
Udgivet eksterntJa

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