GB385320A - Manufacture of cyanine dyes and the application thereof in photography - Google Patents

Abstract

Cyanine dyes are prepared by condensing a 2-methylthiazoline quaternary salt with a quinoline quaternary salt, or with a 2-halogen-quinoline quaternary salt, or with a trialkyl ester of orthoformic acid or of another orthocarboxylic acid, or with a dialkylaminobenzaldehyde. The production of the various classes of cyanine dyes thus obtained is illustrated by examples:--(1) Thiazolino-isocyanines: 2-methylthiazoline methiodide (prepared by refluxing the base with methyl iodide) is condensed in alcohol and in presence of potash with quinoline methiodide, quinoline ethiodide, 6-methylquinoline methiodide and 8-methylquinoline methiodide; similarly 2-methylthiazoline ethiodide (prepared by refluxing the base with ethyl iodide) condensed with quinoline ethiodide and methiodide, and 2-methylthiazoline allyl iodide (prepared by refluxing the base with allyliodide) condensed with quinoline allyliodide yield isocyanine dyes. (2) p Thiazolino-pseudocyanines: 2-methylthiazoline methiodide is condensed in alcohol and in presence of potash with 2 - iodoquinoline methiodide and ethiodide, and similarly 2-methylthiazolino ethiodide with 2-iodoquinoline methiodide and ethiodide. (3) Thiazolinocarbocyanines: 2-methylthiazoline is condensed with methyl-p-toluenesulphonate and the quaternary salt refluxed in pyridine with triethyl orthoformate, trimethyl orthoacetate and trimethyl orthopropionate respectively, and the carbocyanine dyes precipitated by adding potassium iodide; similarly the corresponding 2-methylthiazolino-ethyl-p-toluenesulphonate is first prepared, condensed with triethyl orthoformate and trimethyl orthopropionate respectively and the dyes precipitated by adding potassium iodide. (4) Styrylthiazolines: 2-methylthiazolino methiodide and ethiodide are condensed in methyl alcohol and in presence of piperidine as catalyst with p-dimethylaminobenzaldehyde. The substituents attached to the nitrogen atoms in the above classes of dyes comprise various similar or dissimilar alkyl groups. Instead of starting from the base 2-methylthiazoline itself, substitution products of the latter may be used, for instance 2 : 5-dimethylthiazoline may be converted to a quarternary salt and employed in the above condensations, or 2 : 4 : 5-trimethylthiazoline (prepared from g -bromo-b -aminobutane hydrobromide and thioacetamide) may likewise be used. These products are photosensitizing dyes which may be added to photographic emulsions or incorporated therein by a bathing process. Specifications 359,463, 378,455, and 378,885 are referred to. The Specification as open to inspection under Sect. 91 also relates to sensitizing a photographic emulsion by incorporating with the emulsion, or bathing the emulsion with, a cyanine dye containing a thiazoline nucleus; the use of a thiazolino isocyanine, a thiazolino pseudocyanine, a thiazolino carbocyanine, a 7-alkyl-thiazolinocarbocyanine or a dialkylaminostyrylthiazoline quaternary salt is specified. In the preparation of emulsions a methyl alcohol solution containing 5-100 milligrams of dye is added to a litre of emulsion; generally from 10-20 milligrams of dye is sufficient to obtain maximum sensitivity. This subject-matter does not appear in the Specification as accepted.