Patent GB-418745-A (GB)
Title: Improvements in the sensitisation of photographic emulsions
IPC: G03C1/18
Filed: 1933-04-26
Abstract: Silver halide emulsions are sensitized for ranges about 500m m --710m m  by the incorporation of carbocyanine dyes in which one or both of the benzene rings fused onto the heterocyclic nuclei are substituted in the positions para to the carbon atoms common to the benzene and heterocyclic rings by similar or dissimilar substituents or jointly by a methylene dioxy or ethylene dioxy group.  The dyes are incorporated in the emulsion before casting, in the form of solutions in, for example, methyl or ethyl alcohol or by bathing the finished emulsion in an alcoholic solution of the dye.  Examples are given of the preparation of (1) 1 : 1<1> : diethyl-5 : 6 : 5<1> : 6-tetramethoxy-benzothiocarbocyanine iodide by heating 2-methyl-5 : 6-dimethoxybenzothiazole with paratoluene-sulphonic acid ethyl ester, adding triethyl-orthoformate and pyridine and heating the mixture, and is precipitated by addition of potassium iodide; (2) 1 : 1<1>-diethyl5 : 6 : 5<1> : 6-tetraethoxybenzothiocarbocyanine iodide as in example 1 starting from 2-methyl-5 : 6-diethoxybenzothiazole; (3) 1 : 1<1>-diethyl 5 : 6 : 5<1> : 6<1> : bis-methylenedioxybenzothiocarbocyanine bromide as in example 1 starting with 2-methyl-5 : 6-methylenedioxybenzothiazole; (4) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1>-tetramethylbenzothio-mesomethyl-carbocyanine iodide by heating 2 : 5 : 6-trimethylbenzothiazole with para-toluene-sulphonic acid ethyl ester, adding triethyl-orthoacetate and pyridine, heating the mixture and precipitating the dye with potassium iodide; (5) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1>-tetramethoxybenzothio - mesoethyl - carbocyanine iodide as in example 1 using triethyl-orthopropionate in place of triethyl-orthoformate; (6) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1>-tetraethoxy benzothio-mesomethyl-carbocyanine iodide as in example 2 using triethyl-orthoacetate in place of triethyl-orthoformate; (7) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1>-tetramethoxy-benzoselenocarbocyanine bromide by heating 2-methyl-5 : 6-dimethyl benzoselenazole diethylsulphate with triethyl-ortho-formate in pyridine and precipitating the dye with potassium bromide; (8) 1 : 1<1>-diethyl 5 : 6 : 5<1> : 6<1>-tetraethoxy benzoselenocarbocyanine bromide as in example 7 starting with 2-methyl-5 : 6-diethoxy benzoselenazole diethyl sulphate; (9) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1> bis-ethylenedioxybenzoselenocarbocyanine iodide by condensing 2-methyl - 5 : 6 - ethylenedioxybenzselenazole diethylsulphate with triethyl-ortho-formate and precipitating the dye with potassium iodide; (10) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1>-bis-ethylene dioxybenzoseleno-mesoethyl carbocyanine iodide as in example 9 using triethyl-ortho-propionate in place of trimethyl-ortho-formate; (11) 1 : 1<1>-diethyl-5 : 6 : 5<1> : 6<1>-tetramethoxy benzoseleno-mesoethyl-carbocyanine perchlorate by heating 2-methyl-5 : 6-diethoxybenzoselenodiethyl sulphate with triethyl-orthopropionate in pyridine and precipitating the dye with sodium perchlorate; (12) 1 : 1<1>-diethyl:5 : 6 : 5<1> : 6<1>-tetramethylbenzothio-mesoethyl-carbocyanine iodide as in example 4 using triethylortho-acetate in place of triethyl-orthoformate; (13) 1 : 1<1> diethyl-5 : 5<1>-dimethoxy-6 : 6<1>-diphenylbenzothiocarbocyanine bromide from 2-methyl-5-phenyl-6-methoxybenzothiazole as in example 1; (14) 1 : 1<1>-diethyl-5 : 5<1>-dimeththio - 6 : 6<1>-dimethoxybenzothiocarbocyanine bromide as in example 1 starting with 2-methyl-5 - methoxy - 6 - meththiobenzothiazole; (15) 1 : 1<1>-dimethyl-3 : 3 : 5 : 3<1> : 3<1> : 5<1>-hexamethyl-6 : 6<1>-dichloroindocarbocyanine chloride starting from 1 : 3 : 3 : 5-tetramethyl-6-chloro-2-methyleneindolene as in Specification 232,740, [Class 2 (iii)]; (16) 1 : 1<1>-diethyl-benzoseleno-5<1> : 6<1> - dimethylbenzothio - mesoethyl - carbocyanine iodide by heating 2 - methylbenzoselenazole ethiodide with ethylisothiopropionanilide and heating the product with 2 : 5 : 6 : - trimethylbenzothiazole ethiodine in pyridine and precipitating the dye with potassium iodide; (17) 1 : 1<1>-diethyl-benzothio-5<1> : 6<1>-dimethyl benzothio-mesomethyl-carbocyanine iodide by heating 2-methyl-benzothiazole ethiodide with ethylisothioacetanilide and acetic anhydride and heating the product with 2 : 5 : 6-trimethylbenzothiazole ethiodide in pyridine and precipitating the dye with potassium iodide; (18) 1 : 1<1>-diethyl-benzoseleno - 5<1>-methyl-6<1>-ethoxybenzothio-mesoethyl-carbocyanine iodide by heating the intermediate product of example 16 with 2 : 6-dimethyl-5-ethoxybenzothiazole ethiodide in pyridine and working up as in example 16 (19) 1 : 1<1>-diethyl-6-methoxybenzoseleno-5<1> : 6<1> dimethylbenzothio - mesoethyl - carbocyanine perchlorate by heating the intermediate product from 2 - methyl - 5 - methoxybenzoselenazole ethiodide produced as in example 16 with 2 : 5 : 6-trimethylbenzothiazole ethiodide in pyridine and precipitating the dye with sodium perchlorate.  The preparation of the following bases is described (1) 2 : 5 : 6-trimethylbenzothiazole.  3 : 4-dimethylphenylthiourea is produced from 4-amino-1 : 2-xylene and potassium sulphocyanide and is converted into 2 - amino - 5 : 6 - dimethyl - benzothiazole by means of sulphuryl chloride.  The aminothiazole is converted into 1 : amino-2-mercapto-4 : 5-dimethyl - benzene by means of potassium hydroxide under pressure which yields 2 : 5 : 6 trimethylbenzothiazole when treated with acetic anhydride; (2) 2-methyl-5-methoxy-6-meththiobenzothiazole.  Di - (2 - methoxy - 4-nitrophenyl)-disulphide is formed by acting on 1 - chloro - 2 - methoxy - 4 - nitrobenzene with sodium disulphide and is dissolved in sodium hydrosulphide and methylated giving 1-meththio-2-methoxy nitrobenzene which is reduced to 1-meththio-2-methoxy-4 aminobenzene from which the thiazole is formed.  (3) 2-methyl-5 : 6-ethylenedioxybenzoselenazole is obtained from 1-amino-2-nitro-4 : 5-ethylenedioxybenzene itself prepared by nitrating 4-acetylaminopyrocatechol ethylene ether and eliminating the acetyl group by saponification.  The preparation of the dye 1 : 1-diethyl-5 : 5<1> dimethyl-6 : 6<1>-bis-diethylamino-meso - methyl - benzothiocarbocyanine iodide by heating 2 : 6-dimethyl--5 diethylaminobenzthiazole ethiodide with ethyl-orthoacetate in pyridine and precipitating the dye with potassium iodide is also described.