Two azo pigments based on [beta]-naphthol

There has been much discussion in the literature of the azo-hydrazone tautomerism of pigments. All commercial azo pigments with [beta]-naphthol as the coupling compound adopt the hydrazone tautomeric form (Ph--NH--N=C) in the solid state. In contrast, the red pigments 1-[4-(dimethylamino)phenyldiaze...

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Bibliographic Details
Published in:Acta crystallographica. Section C, Crystal structure communications Crystal structure communications, 2008-09, Vol.64 (9), p.o474
Main Authors: Schmidt, Martin U, Brüning, Jürgen, Wirth, Daniela, Bolte, Michael
Format: Article
Language:English
Subjects:
Chemical compounds
Chemical synthesis
Crystal structure
Crystallography
Pigments
Online Access:Get full text
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Summary:There has been much discussion in the literature of the azo-hydrazone tautomerism of pigments. All commercial azo pigments with [beta]-naphthol as the coupling compound adopt the hydrazone tautomeric form (Ph--NH--N=C) in the solid state. In contrast, the red pigments 1-[4-(dimethylamino)phenyldiazenyl]-2-naphthol, C18H17N3O, (1a), and 1-[4-(diethylamino)phenyldiazenyl]-2-naphthol, C20H21N3O, (1b), have been reported to be azo tautomers or a mixture of azo and hydrazone tautomers in the solid state. To prove these observations, both compounds were synthesized, recrystallized and their crystal structures redetermined by single-crystal structure analysis. Difference electron-density maps show that the H atoms of the hydroxyl groups are indeed bonded to the O atoms. Nevertheless, a small amount of the hydrazone form seems to be present. Hence, the compounds are close to being 'real' azo compounds. Compound (1a) crystallizes with a herring-bone structure and compound (1b) forms a rare double herring-bone structure. [PUBLICATION ABSTRACT]
ISSN:0108-2701
1600-5759
DOI:10.1107/S0108270108023421