GB566520A - Improvements in or relating to the production of coloured photographic images by colour-development - Google Patents

Abstract

A colour coupler for incorporation in a silver salt emulsion or in a developing solution containing an aromatic amino developing agent has the coupling function occurring twice and the two active methylene groups constituting the coupling functions linked by means of sulphur. Examples specified are thio-bis-acetoacetanilide, thio-bis-acetoacetic ethyl ester, thio-bis(1-phenyl-3-methyl-5-pyrazolone) and thio-bis-(1-p-nitrophenyl-3-methyl-5-pyrazolone). The couplers may be used as such or as the inorganic acid salts, if any. In example (1) an ethylene glycol-methyl alcohol solution of thio-bis-(1-phenyl-3-methyl-5-pyrazolone) is added to a developing solution comprising N : N - diethyl - p - phenylenediamine hydro - chloride, sodium sulphite, sodium carbonate and water. In example (2), an ethylene glycolmethyl alcohol solution of thio-bis-acetoacetanilide is added to the same developing solution. The coupler may be incorporated in a separate layer. Thio-bis-pyrazolones are prepared by condensing thio-bis-acetoacetic ester with a phenylhydrazine or by condensing a pyrazolone with sulphur dichloride or thionyl chloride. Thio - bis - (1 - phenyl - 3 - methyl - 5 - pyrazo - lone) is prepared by adding thionyl chloride to a chloroform solution of 1-phenyl-3-methyl-5-pyrazolone. Thio-bis-acetoacetanilides are p prepared by condensing thio-bis-acetoacetic ester with an aniline derivative or by condensing an acetoacetanilide with sulphur dichloride or thionyl chloride. Thio-bis-acetoacetanilide is prepared by adding sulphur dichloride to a benzene solution of acetoacetanilide. Specification 489,161 is referred to.