Patent GB-874011-A (GB)
Title: Cyanine dyestuffs derived from 5-(ª--thienyl)-benzoxazoles and silver halide emulsion layers optically sensitised therewith
IPC: C09B23/10
Filed: 1958-08-18
Abstract: 2-Methyl-5(a -thienyl)-benzoxazole which is used for the preparation of cyanine dyestuffs (see Group IV(c)) is prepared as follows:- <FORM:0874011/IV (b)/1> <FORM:0874011/IV (b)/2> The p-nitrophenyl thiophene used as starting material is reduced to p-aminophenyl thiophene with stannous chloride and hydrochloric acid; the p-aminophenyl thiophene is then diazotised with sodium nitrite and the solution obtained is introduced into boiling copper sulphate solution the p-hydroxyphenyl thiophene formed separating out; the p-hydroxyphenyl thiophene is dissolved in caustic soda solution and diazotised aniline is then added to give the azo dye which is heated with ethanol and caustic soda solution and introduced into a mixture of sodium hydrosulphite and caustic soda in water to give hydroxyamino-phenyl thiophene; the hydroxy amine is then boiled with acetic anhydride to give 2-methyl-5-(a -thienyl)-benzoxazole.  This base can be converted in the usual manner, for example by heating with p-toluene sulphonic acid ethyl ester, dimethyl sulphate, alkyl chlorides, alkyl bromides, alkyl iodides, butane sultone or iodopropionic acid to give quaternary compounds.  Specifications 419,361, 430,357 and 512,494 are referred to.ALSO:The invention comprises cyanine dyestuffs of the general formul <FORM:0874011/IV(c)/1> OR <FORM:0874011/IV(c)/2> in which R represents an alkyl, sulphoalkyl or carboxyalkyl radical; R1, R11 and R111 each represent a hydrogen atom or an alkyl radical; A represents a 5-(a -thienyl)-benzoxazole radical or an unsubstituted benzthiazole, naphthiazole, thiazole, benzselenazole, selenazole, benzoxazole, naphthoxazole or quinoline ring system; Q represents the atoms needed for completing a heterocyclic ketomethylene ring which may be linked by way of a methine group to a 5-(a -thienyl)-benzoxazole ring; and n and m each represent 0, 1 or 2. Asymmetrical 2, 21-monomethinecyanines (pseudo cyanines) are obtained by condensing the quaternary salts of 2-methyl-5-(a -thienyl)-benzoxazole, <FORM:0874011/IV(c)/3> with quaternary salts of heterocyclic nitrogen compounds which contain an alkylmercapto group in the a - or g -position, suitable heterocyclic nitrogen compounds being, for example, substituted or unsubstituted benzthiazoles, naphthiazoles, thiazoles, benzselenazoles, benzoxazoles, naphthoxazoles and quinolines.  In addition to the alkyl mercapto group the compounds may be substituted by one or more alkoxy, halide, alkyl, aryl, aralkyl, amino, or substituted amino groups.  Symmetrical monomethine-cyanines are obtained by condensation the salts of 2-methyl-5-(a -thienyl)-benzoxazole with amyl nitrite in glacial acetic acid.  Symmetrical carboxycyanines are produced by condensing the quaternary salts by means of ethyl orthoformate in pyridine solution.  Asymmetrical carbocyanines, unsubstituted in the trimethine chain, are obtained by condensing the quaternary salts with heterocyclic nitrogen bases of the type previously mentioned which are substituted in the a -position by an acyl-aryl-amino-vinyl group such as an acetyl-phenyl-amino-vinyl group.  Symmetrical carbocyanines which are substituted at the middle carbon atom of the trimethine chain by an alkyl group are obtained by condensing the quaternary thienyl bases with an ortho-ester of acetic acid or of a higher fatty acid.  By condensing the above-mentioned quaternary salts with quaternary salts of heterocyclic nitrogen bases which contain a <FORM:0874011/IV(c)/4> group in the a -position asymmetrical carbocyanines are obtained which are substituted in the trimethine chain by an alkyl group. Symmetrical pentamethine, heptamethine and nonamethine-cyanines may also be obtained from the quaternary thienyl bases by known methods, such as by condensing the bases with aniline acrolein anil or glutaconic aldehyde dianilide in alcoholic solution with sodium ethoxide.  Merocyanines may be obtained by condensing the quaternary salts of the thienyl-benzthiazoles with compounds of the formula:- <FORM:0874011/IV(c)/5> in which R2 is an alkyl radical, R3 is an alkoxy or anilino group and Y is oxygen or sulphur.  These merocyanines correspond to compounds <FORM:0874011/IV(c)/6> <FORM:0874011/IV(c)/7> <FORM:0874011/IV(c)/8> <FORM:0874011/IV(c)/9> of the general formula VIa.  It is also possible to condense any other known quaternary merocyanine salts such as those of general formula X with one of the above quaternary salts of thienyl benzoxazole to give rhodacyanines of general formula VIII.  The quaternary salts of thienyl benzoxazole may also be used for the production, by known methods, of isocyanines of the general formula IX.  The cyanine dyestuffs referred to above may be used for optically sensitizing silver halide emulsion layers (see Group XX). Specifications 419,361, 430,357 and 512,494 are referred to.