GB415949A - Process for sensitising photographic silver halide emulsions - Google Patents

Abstract

Silver halide emulsions are sensitized especially to the yellow and green by the use of symmetrical naphthoxocarbocyanine dyes substituted at the central carbon atom of the trimethine chain and derived from 2-methyl-a -or -b -naphthoxazole. These dyes are prepared by condensing a quaternary ammonium salt of a 2-methyl-a - or b -naphthoxazole with a trialkyl ester of an orthocarboxylic acid containing more than one carbon atom or according to the process described in Specification 412,309. In examples (1) 1 : 1<1>-dimethyl-mo-ethyl-b -naphthoxocarbocyanine bromide is prepared by heating 2-methyl-b -naphthoxazole dimethyl sulphate with triethyl orthopropionate in pyridine and precipitating with potassium bromide; (2) 1 : 1<1>-dimethyl-mo-ethyl-a -naphthoxocarbocyanine bromide is prepared as in example 1 starting with 2-methyl-a -naphthoxazole; (3) 1 : 1<1>-dimethyl-mo-methyl-a -naphthoxocarbocyanide bromide is prepared by heating 2-methyl-a -naphthoxazole dimethyl sulphate with triethyl orthoacetate in pyridine and working up as in example 1; (4) by using triethyl orthothiophenate in place of triethyl orthoacetate as in example 3 the dye 1 : 1<1> dimethyl-mo-thienyl-a -naphthoxocarbocyanine bromide is formed; (5) by using triethyl orthobenzoate in place of triethyl orthoacetate as in example 3 the dye 1 : 1<1>-dimethyl-mo-phenyl-a -naphthoxocarbocyanine bromide is formed; and (6) 1 : 1<1>-dimethyl-mo-ethyl-b -naphthoxocarbocyanine bromide is prepared by heating 2-methyl-b -naphthoxazole dimethyl sulphate with ethylisothio propionic acid anilide in pyridine and precipitating the dye in the form of bromide. Specification 403,845 also is referred to.