5 - Chloro - 2 - methylbenzthiazole p - sulphobenzylbromide is prepared by heating together 5-chloro-2-methylbenzthiazole and p-sulphobenzyl bromide. 2-Methylbenzthiazole p-sulphobenzylbromide and lepidine p - sulphobenzylbromide are similarly prepared. p-Sulphobenzyl bromide is prepared by heating together p-toluenesulphonic acid and bromoform, and adding bromine dropwise. 5 - Chloro - 2 - methylbenzthiazole b - sulphoethylbromide is prepared by heating together 5 - chloro - 2 - methylbenzthiazole and 2 - bromoethanesulphonic acid. 2-Methyl-a -naphthathiazole b - sulphoethylbromide, 2 - methylbenzthiazole b - sulphoethylbromide, and 2 : 3 : 3 - trimethylindolenine b - sulphoethylbromide are similarly prepared. 2-Bromoethanesulphonic acid is prepared by stirring together sodium 2 - bromoethanesulphonate, an ethyl alcohol solution of dry HCl, and ethyl alcohol. Lepidine carboxymethobromide is prepared by refluxing together lepidine carbethoxymethobromide and 48 per cent hydrobromic acid. Cyclammonium sulphoalkyl iodides and per chlorates are prepared by adding concentrated aqueous solutions of potassium iodide and of sodium perchlorate to hot methyl alcohol solutions of the cyclammonium sulphoalkyl bromide. Cyclammonium sulphoalkyl chlorides, acetates, and thiocyanates are prepared by stirring the bromides with boiling methyl alcohol suspensions of silver chloride, acetate, and thiocyanate, filtering off the silver salts, and isolating from the methyl alcohol solutions. 2 - (4 - Acetanilido - 1 : 3 - butadienyl) - 5 - chlorobenzthiazol b -carboxyethiodide is prepared by refluxing together 5-chloro-2-methylbenzthiazole b -carboxyethiodide, b -anilinoacrolein anil hydrochloride and acetic anhydride. Specifications 606,141, 645,288, 647,542 and 649,725 are referred to.ALSO:Dyes of the general formula <FORM:0654683/IV (c)/1> wherein R is a carboxyalkyl or sulphoalkyl group, L is a methine group, n is 1 or 2, and Q and Z are the atoms necessary to complete heterocyclic nuclei containing 5 or 6 atoms in the heterocyclic ring are prepared by condensing a cyclammonium carboxyalkyl or sulphoalkyl quaternary salt containing in the a - or g -position to the quaternary N atom a thioether group or halogen atom with a heterocyclic compound of the general formula <FORM:0654683/IV (c)/2> The condensation may be effected in the presence of an alcoholic solution of an alkali metal hydroxide. 5 - [3 - b - Carboxyethyl - 2(3) - benzthiazolylidene]-3-ethylrhodanine is prepared by heating together 2-phenylmercaptobenzthiazole and b -iodopropionic acid, adding 3-ethylrhodanine, triethylamine, and ethyl alcohol and boiling. Dyes of the general formula <FORM:0654683/IV (c)/3> are prepared by condensing a cyclammonium carboxyalkyl or sulphoalkyl quaternary salt containing in the a - or g -position to the quaternary N atom a b -arylaminovinyl group (which may be acylated), or a b -alkylmercaptovinyl group, or by condensing a cyclammonium carboxyalkyl or sulphoalkyl quaternary salt containing in the a - or g - position to the quaternary N atom a -CH2R4 group (R4 being H or alkyl) with an arylaminomethylene compound of the general formula <FORM:0654683/IV (c)/4> (wherein R5 is H or an acyl group and R6 is an aryl group). 5 - [(3 - Carboxymethyl - 2(3) - benzoxazolylidene) - ethylidene] - 3 - ethylrhodanine is prepared by refluxing together 2-b -acetanilidovinylbenzoxazole carboxymethobromide, 3 - ethylrhodanine, triethylamine, and ethyl alcohol. 3 - b - Carboxyethyl - 5 - [(3 - carboxymethyl - 2(3) - benzoxazolylidene) - ethylidene] - rhodanine is similarly prepared. 5-[(3-b -Carboxyethyl - 2(3) - benzthiazolylidene) - isopropylidene]-3-ethylrhodanine is prepared by heating together 3 - b - carboxyethyl - 2 - thioacetylmethylenebenzthiazoline and methyl p-toluenesulphonate, adding 3-ethylrhodanine, triethylamine, and ethyl alcohol, and refluxing. 5-[(3-b - Carboxyethyl - 2(3) - benzthiazolylidene) - a - ethylethylidene] - 3 - ethylrhodanine and 5 - [(3 - b - carboxyethyl -2(3) - benzthiazolylidene) - a - ethylethylidene] - 3 - ethyl - 2 - thio - 2 : 4(3 : 5) - oxazoledione are similarly prepared. 5-[(3-b -Carboxyethyl - 2(3) - benzthiazolylidene) - ethylidene] - 3-ethylrhodanine is prepared by refluxing together 2 - methylbenzthiazole - b - carboxyethiodide, 5 - acetanilidomethylene - 3 - ethylrhodanine, triethylamine, and ethyl alcohol. 5 - [(3 - b - Carboxyethyl - 2(3) - benzoxazolylidene) - ethylidene] - 3 - ethylrhodanine, 5 - [(3 - carboxymethyl - 2(3) - a - naphthathiazolylidene) - ethylidene] - 3 - ethylrhodanine, 5 - [(3 - carboxyethyl - 2(3) - thiazolinylidene) - ethylidene] - 3 - ethylrhodanine, 4 - [(3 - b - carboxyethyl - 2(3) - benzthiazolylidene) - ethylidene) - 3 - methyl - 1 - phenyl - 5 - pyrazolone, 4 - [(1 - b - carboxyethyl - 3 : 3 - dimethyl - 2(1) - indolylidene) - ethylidene] - 3 - methyl - 1 - phenyl - 5 - pyrazolone, 5 - [(1 - carboxymethyl - 4(1) - quinolylidene) - ethylidene] - 3 - ethylrhodanine, 5 - [(3 - b - carboxyethyl - 2(3)-benzthiazolylidene) - ethylidene] - 3 - ethyl - 1 - phenyl - 2 - thiohydantoin, 5 - [(3 - b - carboxyethyl - 2(3) - benzthiazolylidene) - ethylidene] - 3 - ethyl - 2 - thio - 2 : 4(3 : 5) - oxazoledione, and 5 - [(5 - chloro - 3 - b - sulphoethyl - 2(3) - benzthiazolylidene) - ethylidene] - 3 - ethylrhodanine triethylamine salt are similarly prepared. Dyes of the general formula <FORM:0654683/IV (c)/5> are prepared by condensing a cyclammonium carboxyalkyl or sulphoalkyl quaternary salt containing in the a - or g - position to the quaternary N atom a 4-arylamino-1 : 3-butadienyl group (which may be acylated) with a heterocyclic compound of the formula given above, or by condensing a cyclammonium carboxyalkyl or sulphoalkyl quaternary salt containing in the a - or g -position to the quaternary N atom a -CH2R4 group (wherein R4 is H or alkyl) with an arylaminoallylidene compound of the general formula <FORM:0654683/IV (c)/6> (wherein R7 is H or an acyl group and R8 is an aryl group). 5 - [(3 - b - Carboxyethyl - 5 - chloro-2(3)-benzthiazolylidene) - 1 : 3 - butadienylidene)-rhodanine is prepared by refluxing together 2-(4-acetanilido-1 : 3-butadienyl)-5-chlorobenzthiazole b -carboxyethiodide, rhodanine, triethylamine, and ethyl alcohol. 5-[(3-b -Carboxyethyl - 2(3) - benzoxazolylidene) - 1 : 3 - butadienylidene) - 1 : 3 - diethylbarbituric acid is prepared by refluxing together 5-g -acetanilidoallylidene-1 : 3-diethylbarbituric acid, 2-methylbenzoxazole-b -carboxyethiodide, triethylamine, and ethyl alcohol. Merotricarbocyanine dyes are prepared by condensing a cyclammonium carboxyalkyl or sulphoalkyl quaternary salt containing in the a - or g -position to the quarternary N atom a -CH2R4 group (R4 being H or alkyl) with an arylamino-2 : V-pentadienylidene compound of the general formula <FORM:0654683/IV (c)/7> wherein R0 is H or acyl and R10 is aryl. 5-[(3-b -Carboxyethyl - 2(3) - benzoxazolylidene) - 2 : 4 - hexadienylidene - 1 : 3 - diphenyl - 2 - thiobarbituric acid is prepared by refluxing together 5-(5-acetanilido - 2 : 4 - pentadienylidene) - 1 : 3 - diphenyl - 2 - thiobarbituric acid, 2 - methylbenzoxazole-b -carboxyethiodide, triethylamine, and ethyl alcohol. Dyes of the general formula <FORM:0654683/IV (c)/8> wherein m is 1 to 4, Q1 is O, S, or -N-R2 (R2 being alkyl or aryl), R1 is alkyl or aryl, and d i 2 or 3, are prepared by treating a merocyanine dye of the general formula <FORM:0654683/IV (c)/9> with an alkyl ester to obtain a quaternary alkylmercapto compound and then condensing with a heterocyclic compound of the formula given above. 5-[(3-b -Carboxyethyl-2(3)-benz-oxazolylidene) - ethylidene] - 3 - ethyl - 5 - (3 - ethyl - 4 - oxo - 2 - thiono - 5 - thiazolidylidene) - 4 - thiazolidone is prepared by heating together 5-[(3-b -carboxyethyl 2(3)-benzoxazolylidene)-ethylidene] - 3 - ethylrhodanine and methyl p toluenesulphonate, dissolving the washed product in pyridine, adding 3 ethylrhodanine and triethylamine, and refluxing. Specifications 606,141, 645,288, 647,542 and 649,725 are referred to.