GB418157A - Improved process of sensitising silver halide emulsion layers - Google Patents

Abstract

Silver halide emulsions are sensitized by the use of aminosubstituted benzthiocarbocyanine dyes having an alkyl group attached to the middle carbon atom of the trimethine chain. The amino groups may be unsubstituted or may be substituted by, for example, methyl, ethyl, propyl, or acetyl groups. Examples are given of the preparation of (1) 1 : 1<1>-diethyl-6 : 6<1> - bisdiethylaminobenzthio - b - methyl carbocyanine iodide by heating 2-methyl-5-diethylaminobenzthiazole ethyl iodide with ethyl orthoacetate in dry pyridine; (2) 1 : 1<1>-diethyl - 6 : 6<1> - bis - diethylaminobenzthio - b - ethyl-carbocyanine perchlorate by heating the base of (1) with ethyl orthopropionate in dry pyridine; and (3) 1 : 1<1>-diethyl-5 : 5<1>-bisdiethylamino-b -methyl-carbocyanine perchlorate by heating 6-diethylamino-2-methylbenzthiazole with ethyl orthoacetate in dry pyridine. In examples 2 and 3 the dye is precipitated by the addition to the solution in pyridine of sodium perchlorate. The base 2-methyl-5-diethylaminobenzthiazole ethyliodide is prepared from para-bromodiethylaniline analogously to the production of 2-methyl-5-dimethylaminobenzthiazole described in example 2 of the parent Specification and the base 6-diethylamino-2-methylbenzthiazole is prepared as described in example 1 of the parent Specification. The Specification as open to inspection under Sect. 91 describes also the preparation and use of benzselenazole dyes. In examples: (1) 1 : 1<1>-diethyl-5 : 5<1>-bis-acetylaminobenzseleno-b -methyl-carbocyanine bromide is prepared by heating 6-acetylamino-2-methyl-benzselenazole ethyl sulphate with ethyl orthoacetate in pyridine; and (2) 1 : 1<1>-dimethyl-5 : 5<1>-bispropionylaminobenzselenazole - b - ethyl - carbo - cyanine bromide is prepared by heating 6 - propionylamino - 2 - methyl - benzselenazole dimethyl sulphate with ethyl orthopropionate in dry pyridine, the dyes being precipitated with potassium bromide in both cases. The selenazole bases are prepared by the action of acetic or propionic anhydride on 2-methyl-6-aminobenzselenazole prepared by nitrating 2-methyl benzselenazole and reducing the nitro group with stannous chloride and hydrochloric acid or iron powder and acetic acid. This subject-matter does not appear in the Specification as accepted.