Patent GB-853724-A (GB)
Title: Oxazolo benzothiazole derivative sensitizing dye intermediates
IPC: G03C1/12
Filed: 1958-02-21
Abstract: The invention comprises new compounds of the general formula <FORM:0853724/IV(b)/1> in which R is an alkyl or aralkyl group and R1 is an alkyl, aryl or aralkyl group; and the quaternary salts of these compounds.  The free bases are prepared as follows: 2-amino-5-hydroxy thiophenol is prepared by the alkali fusion of a 2-amino- or a 2-mercapto-6-methoxybenzothiazole; to the solution of alkali salts of 2-amino-5-hydroxythiophenol is added an acid anhydride, e.g. acetic, propionic or butyric anhydride, or an acyl halide, e.g. acetyl, propionyl, phenylacetyl or phenylpropionyl chloride; a 6-acyloxybenzothiazole substituted in the 2-position by an aralkyl or alkyl group thereby being found.  This compound is saponified by dilute alkali to give 6-hydroxy-2-alkyl (or aralkyl) benzothiazole which is coupled with a diazonium salt such as phenyldiazonium chloride to give the 2 - alkyl - 5 - phenyldiazo - 6 - hydroxybenzothiazole.  Reduction of the aryldiazonium group, e.g. with sodium hydrosulphite in alkaline medium, gives the 2-alkyl-5-amino-6-hydroxybenzothiazole. Finally acylating the amino or hydroxyl group or both groups, followed by distillation gives the desired 2. 6-disubstituted oxazolo benzothiaazole.  These bases may be quaternated by conventional methods.  For example they may be heated with methyl or ethyl iodide under pressure.  The quaternary salts may be obtained with compounds of formula (R2X) in which R2 is alkyl, b -hydroxyethyl, g -hydroxypropyl, carboxyalkyl or aralkyl and X is an anion such as chloride, bromide, iodide, perchlorate or p-toluenesulphonate.  The quaternary salts are used in the production of sensitising dyes (see Group IV(b)) which may be used in photographic emulsions (see Group XX).ALSO:Quaternary salts of new oxazolo [4,5-f]-benzothiazoles having the general formula: <FORM:0853724/IV (c)/1> in which R is alkyl or aralkyl; R1 is alkyl, aryl or aralkyl; R2 is alkyl, hydroxyalkyl, carboxyalkyl or aralkyl; and X is an anion, are converted to sensitizing dyes of formula: <FORM:0853724/IV (c)/2> in which n is an integer of from 1 to 4; m is 1 or 2; A is hydrogen or a lower alkyl group; R3 is alkyl, hydroxyalkyl, carboxyalkyl or aralkyl; and Z represents the atoms necessary to complete a 5- or 6-membered nitrogenous heterocyclic system of the type used in cyanine dyes, such as pyridine, lepidine, quinoline, indoline, oxazole, thiazoline, thiazole, selenazole, selenazoline, oxazoline, benzothiazole, benzoselenazole, benzoxazole and naphthothiazole.  The conversion is brought about by heating the oxazolobenzothiazonium salts in the presence of an acid-binding agent, such as pyridine, trimethylamine or triethylamine, with a cyclammonium quaternary salt having a reactive grouping on the carbon atom in the 2-position of the heterocyclic ring, such as a halogen atom, an alkyl mercapto group, an alkylmercaptovinyl group, an alkyl mercaptoalkylvinyl group, a b -acetanilidovinyl group, a 4- acetanilido -1, 3- butadienyl group or a 6- acetanilido -1, 3, 5- hexatrienyl group.  These dyes may be used to increase the sensitivity of photographic emulsions (see Group XX).