GB423827A - Process for sensitising photographic silver halide emulsions - Google Patents

Abstract

Silver halide emulsions are sensitized, mainly to the blue and blue-green portions of the spectrum by pseudocyanine dyes unsubstituted at the methine carbon atom and derived from a substituted or unsubstituted benzoxazole. The dyes are prepared by condensing a quaternary ammonium salt of substituted or unsubstituted 2-methylbenzoxazole with a 2-iodo derivative of a heterocyclic base or with a 2-thio-keto-derivative as described in Specification 423,792. Examples are given of the preparation of (1) 1<1>-methyl-1<1>-ethyl-6<1>-methylbenzoxoquino - pseudocyanine iodide by heating 2-methylbenzoxazole dimethyl sulphate with N-ethyl-6-methylthioquinolone ethiodide in pyridine and piperidine; (2) 1-methyl-1<1>-ethyl - 5 - methoxy - 6<1> - methyl - benzoxoquino-pseudocyanine iodide from 2-methyl-6-methoxy-benzoxazole di-methyl sulphate as in example (1); (3) 1-methyl-1<1>-ethyl-6<1>-methyl-4 : 5-benzo-benzoxoquino-pseudocyanine iodide by heating 2-methyl-a -naphthoxazole dimethylsulphate with N-ethyl-6-methylthioquinolone ethiodide in pyridine and piperidine; and (4) 1 - methyl - 1<1> - ethyl - 6<1> - methyl - 6 : 7 - benzobenzoxo-pseudocyanine iodide by heating 2-methyl-b -naphthoxazole dimethylsulphate with N-ethyl-6-methyl-thioquinolone ethiodide, in pyridine and piperidine. The 2-methyl-6-methoxy-benzoxazole used in example (2) is prepared by distilling 5-methoxy-2-acetylamino-1-phenol.