Isomeric structure of α-amino substituted anthraquinones

Abstract

α-Amino substituted anthraquinones are the key compounds in the synthetic dyes chemistry. To their studying are devoted thousands of articles and patents, where they have been invariably considered as the substituted 9,10-anthraquinones. So long, as 1,4-diamino[1] and 1-amino-4-hydroxyanthraquinones [2] were found to neither individual compounds or 9,10anthraquinone derivatives. They are characterized by amino-imino [1, 2] and the keto-enol [2] tautomerism. They exist as equilibrium dynamic mixtures of tautomers of 1,10and 1,4-quinoid structure. The question arises as to whether such structural features are common to the amino anthraquinones or they are inherent in 1.4-disubstituted derivatives only. The answer can be taken by the quantum chemical studying and correlation analysis of not the separate measurements of electronic absorption spectra, but of extensive collection of published data on the electronic spectra of αamino anthraquinones. The influence of isomerization on the electronic spectra of 1-amino-, 1,5 and 1,8-diaminoanthraquines was retraced by the quantum chemical calculations. In the visible field of the experimental spectra of 1-amino anthraquinone usually there are one or two πl,π*-bands responsible for the compound color. Their position found by the different authors is varied considerably, for example, in ethanol solution: 430, 441, 470, 475, 481, 490, 497 nm. Nonrandom nature of the extreme values in this series was confirmed by a number of the independent measurements in similar media, for example: 434 nm in 2-propanol or 488 nm in ochlorophenols [3]. The correlation analysis of these data showed that the samples obtained by the different methods are not identical to each other and have different structures: 1-amino-9,10(I) and 9-amino1,10-anthraquinone (II), each of which is in an equilibrium with tautomeric imino-forms (III, IV). Some of them are able to exist as conformers, such as IIa, not containing intramolecular hydrogen bonds. DOI: 10.1134/S107036321110029X