GB402458A - Improvements in photographic sensitisers - Google Patents

Abstract

Carbocyanine dyestuffs suitable for sensitizing silver halide emulsions are obtained by condensing a quaternary salt of a 2-methyl -a -naphthothiazole containing a nuclear alkyloxy group with an alkyl ester of ortho acetic acid. The dyestuffs may be added to the emulsion at any step of its production in alcoholic solution. In an example 1 - methyl - 6 - methoxy - a - naphthothiazole ethyliodide is condensed with ethyl orthoacetate. The halides, perchlorates, para toluenesulphonates, alkylosulphates and nitrates of the dyestuffs are mentioned. The naphthothiazoles used as starting materials may be prepared by the known methods for the preparation of unsubstituted naphthothiazoles. The Specification as open to inspection under Sect. 91 comprises also the production and use as photographic sensitizers of carbocyanine dyestuffs derived from a 2-methyl derivative of any substituted a or b naphthothiazole quaternary salt. The nuclear substituted alkyl, halogen, amino and substituted amino, e.g., alkyl, aryl and acyl amino, derivatives of the naphthothiazoles are mentioned. In further examples the following dyestuffs are prepared: 1 : 1<1>-diethyl - 5 : 5<1> - diethoxy - b - naphthothio - meso-ethylcarbocyanine-bromide, 1 : 1<1> : 5 : 5<1> - tetramethyl - a - naphthothio - meso - methyl - carbocyaninebromide, 1 : 1<1> - dimethyl - 5 : 5<1> - diethoxy - a - naphthothio - meso - methylcarbocyaninebromide, 1 : 1<1> - diethyl - 5 : 5<1> - dimethoxy - a - naphthothiocarbocyaninebromide and 1 : 1<1> - diethyl - 6 : 6<1> - dimethoxy - a - naphthothiocarbocyanine. This subject-matter does not appear in the Specification as accepted.