Patent GB-438420-A (GB)
Title: Improvements in or relating to the production of compounds of the cyanine type
IPC: C09B23/04
Filed: 1934-05-08
Abstract: Cyanine dyes are prepared by reacting an N-alkylthione of a heterocyclic nitrogen compound with an alkyl-p-toluenesulphonate and with a quaternary ammonium salt of a heterocyclic nitrogen compound having a reactive methyl group.  The N-alkylthione may first be reacted with the alkyl-p-toluenesulphonate to form a quaternary salt which is then reacted with the quaternary ammonium salt of a heterocyclic nitrogen compound having a reactive methyl group, or the N-alkylthione of a heterocyclic nitrogen compound, the heterocyclic nitrogen compound having a reactive methyl group and an alkyl-p-toluenesulphonate are all mixed together and the reaction carried out in one step.  Reaction may be effected in presence of a solvent (for example alcohol) and of an acid-binding (sodium acetate); a solvent such as pyridine may combine both functions. N-alkylthione and reactive methyl derivatives of unsubstituted and substituted thiazoles, thiazolines, oxazoles, oxazolines, selenazoles, selenazolines, quinolines, indolenines and pyridines may be used; the substituent radicles may be alkyl, aralkyl or aryl and in the case of polycyclic compounds substituents on the carbocyclic rings may be hydroxy, alkoxy, halogen, alkyl, aryl, aralkyl, amino or substituted amino.  Some of the dyes are of use as sensitizing agents in photographic emulsions, for which purpose they may be incorporated in light-sensitive emulsions before casting or the emulsion-coated film may be passed through a bath containing the dyes.  In examples: (1) 1 - methylquinoline - 2 - thione, 2 , 4 - dimethylthiazole and ethyl-p-toluenesulphonate are heated together in pyridine and the dye precipitated out as the iodide; 2.4-dimethylthiazole may be replaced by quinaldine; (2) 1 - methylbenzoxazole, N - methylbenzoxazole - 1 - thione and methyl - p - toluenesulphonate are heated together in pyridine and the dye precipitated as the iodide; (3) 1-methylbenzthiazole, N-ethylbenzoxazole-1-thione and ethyl-p-toluenesulphonate are heated together in alcohol and presence of sodium acetate and the dye precipitated out as the iodide; (4) N-methylbenzoxazole - 1 - thione, a  - picoline and methyl-p-toluenesulphonate are heated together in pyridine and the dye precipitated as the iodide; (5) N-methylpyridine-2-thione, 1-methylbenzthiazole and methyl-p-toluenesulphonate are heated together in pyridine and the dye precipitated as the iodide; (6) N-methylbenzoxazole-1-thione is reacted with methyl-p-toluenesulphonate and the salt obtained with 2 . 3 . 3 - trimethylindolenine - methiodide in pyridine; (7) N - methylbenzthiazole - 1 - thione, b -naphthaquinaldine, and methyl-p-toluene-sulphonate are reacted together in pyridine and the dye precipitated out as the bromide; (8) N - methylbenzthiazole - 1 - thione, 2 . 4 - dimethyloxazole and methyl-p-toluenesulphonate are reacted together in pyridine and the dye precipitated as the iodide; (9) 2.4.5-trimethylbenzoxazole - 1 - thione, 1 . 4. 5 - trimethylbenzoxazole and methyl-p-toluenesulphonate are reacted together in pyridine and the dye precipitated as the bromide. Sensitizing data for some of these products are given.  Samples have been furnished under Sect. 2 (5) of (a) 1 . 3 . 3 . 2<1>-tetramethylindoxacyanine iodide prepared by heating 1 . 3 . 3 - trimethyldihydroindole - 2 - thione, 1 - methylbenzoxazole and methyl - p - toluenesulphonate in pyridine and pouring the mixture into potassium iodide solution; (b) 2-ethyl-1<1>-methylthioisocyanine iodide prepared by heating 2-ethyldihydrobenzthiazole-1-thione, lepidine and methyl-p-toluenesulphonate in pyridine and pouring the mixture into potassium iodide solution.  The N-alkylthione derivatives are generally prepared by methods analogous to those described in the literature in connection with the N-alkylthiones of pyridine, benzoxazole and benzthiazole, or analogous to the preparation of N-methylquinoline-4-thione by reacting 4-chlorquinoline with methyliodide and the product with alcoholic potassium hydrogen sulphide.  The thiazolothiones are prepared by condensing N-alkyldithiocarbamic acid salts with halogenated ketones of the monochloracetone or w-bromacetophenone types.  Specifications 423,792 and 424,559 are referred to.