Patent GB-412309-A (GB)
Title: Manufacture of dyes and intermediates therefor, and photographic emulsions sensitised therewith
IPC: C09B23/06
Filed: 1933-01-17
Abstract: Carbocyanine dyes substituted at the central carbon atom of the trimethine chain by an alkyl, aryl or aralkyl radicle or intermediates therefor are prepared by condensing a quaternary ammonium compound of a heterocyclic base containing a reactive methyl group in a -position with a thioimide of the general formula <FORM:0412309/IV/1> wherein R3 represents alkyl, aryl, aralkyl, R4 represents alkyl and R5 a phenyl or substituted phenyl radicle.  The dyes are derived by condensing the quaternary salt with \ba1/2\be--1\ba1/2\be molecular proportions of thioimide in presence of a basic condensing agent, such as pyridine. Intermediates are formed by condensation in the absence of a condensing agent, or in the presence of an acid condensing agent, such as acetic or propionic anhydride or glacial acetic acid; in the first case an arylidovinyl type of compound is probably obtained, whereas in the second case (which is preferred when the desired intermediate is to be employed in the preparation of a ms-methyl as distinct from a ms-ethyl substituted carbocyanine) a thiovinyl type of compound is obtained. Both types of intermediates, on condensation in presence of a basic condensing agent with a quaternary ammonium compound of a heterocyclic base containing a reactive methyl group in a -position, yield symmetrical or unsymmetrical polymethine dyes.  Suitable quaternary ammonium salts for these processes may be comprised by the general formula <FORM:0412309/IV/2> wherein Y represents CR1 R2 (R1, R2 stand for alkyl, aryl), O, S, Se, r represents alkyl, R represents vinylene, phenylene, naphthylene or the radicle of a polynuclear ring system, such as anthracene, phenanthrene, fluorene, or diphenyleneoxide, and x is an anion such as Cl, Br, I, ClO4.  In the first formula above R3 and R4 may stand for methyl, ethyl, propyl, butyl, amyl, isoamyl and in the case of R3 also for phenyl, tolyl, alkoxyphenyl.  In examples: (1) 2-methylbenzthiazole ethiodide is condensed with ethyl isothioacetanilide in presence of acetic anhydride, and the resulting thiovinyl derivative condensed in presence of pyridine alone or admixed with piperidine with 2-methylbenzthiazole ethiodide,2-methyl-4,5-benzobenzthiazole dimethylsulphate, 5-diethylamino-2-methylbenzthiazole ethiodide and 2-methyl-6,7-benzobenzthiazole dimethylsulphate; (2) 2-methylbenzthiazole ethiodide is condensed with ethyl isothiopropionanilide and the resulting intermediate condensed in presence of pyridine with 2-methyl-5-methoxybenzselenazole ethiodide, 2-methyl-4,5-benzobenzthiazole dimethylsulphate, 2-methylbenzthiazole ethiodide, 2-methyl -6,7 - benzobenzthiazole diethylsulphate 2-methylbenzselenazole ethiodide and 2-methylbenzoxazole ethiodide; (3) 2-methylbenzthiazole methiodide is condensed with ethyl isothiopropionanilide and the resulting intermediate condensed with 2-methyl-6,7-benzobenzthiazole diethylsulphate; (4) 2-methylbenzthiazole ethiodide is condensed in presence of acetic anhydride with S-ethylisothiophenyl acetanilide and the resulting intermediate is condensed with 2-methylbenzselenazole ethiodide; (5) 2-methylbenzselenazole ethiodide is condensed with ethyl isothioacetanilide in acetic anhydride and the resulting intermediate condensed with 2-methylbenzselenazole ethiodide, 5-diethylaminobenzthiazole ethiodide, and 2-methyl-4,5-benzobenzthiazole dimethylsulphate in presence of a mixture of pyridine and piperidine; (6) 2-methylbenzselenazole ethiodide is condensed with ethyl isothiopropionanilide and the resulting intermediate condensed with 2-methyl-5-methoxybenzselenazole ethiodide and 2-methyl-4,5 - benzobenzthiazole dimethylsulphate in presence of pyridine; (7) symmetrical dyes are obtained by condensing 5-methoxy-2-methylbenzselenazole ethiodide in presence of pyridine with ethyl isothiopropionanilide, ethyl isothiobutyranilide and ethyl isothio-p-methoxybenzanilide. Both symmetrical and unsymmetrical dyes sensitize silver halide emulsions and sensitizing data are given in the case of each product described in the examples.  The use in sensitizing silver halide emulsions of those unsymmetrical dyes whose asymmetry is independent of any dissimilarity between the radicles (r) attached to the quaternany nitrogen atom forms part of the invention.  The dyes are added in amounts of 5-40 milligrams per kilo emulsion; they may be incorporated in the emulsion in the form of solutions, or applied by coating the cast but not dried emulsion layer with a solution of the dye, or by bathing the finished photographic material in such a solution.  The spectrograms of some of the above unsymmetrical dyes are given.  Specification 334,706, [Class 2 (iii)], also is referred to.  Heterocyclic bases serving as parent materials for the dyes are prepared analogously to known methods.  Substituted benzoxazoles are obtained by condensing substituted o-aminophenols with acetic anhydride.  Substituted benzthiazoles and benzoselenazoles are prepared as described in Specification 394,537.  Amino substituted benzthiazoles are prepared as described in Specification 400,951 or according to the processes (a) 6-amino-2-methylbenzthiazole is prepared as described in Specification 313,293, [Class 2 (iii)]; (b) 5-amino-2-methylbenzthiazole is prepared by reducing the corresponding nitro compound with iron and acetic acid; (c) 7-amino-2,4,6-trimethylbenzthiazole is prepared by converting 2,4-dimethyl-5-acetylaminoaniline into 4,6-dimethyl-7-acetylamino-2-aminobenzthiazole according to Specification 295,295, [Class 2 (iii)], saponifying this with strong aqueous alkali according to Specification 306,590, [Class 2 (iii)], and heating the resulting o-aminomercaptan with acetic anhydride. Substituted naphthothiazoles may be prepared in a manner analogous to the following: 2-amino-7-methoxynaphthalene is acetylated, converted to the thioaceto compound by means of phosphorus pentasulphide and oxidized with potassium ferricyanide in alkaline solution to give 2-methyl-8-methoxy-a -naphthothiazole. S-Ethylisothiophenylacetanilide is prepared by treating phenyl acetanilide with phosphorus pentasulphide, and converting this thioaceto compound in known manner by means of sodium ethylate and ethylbromide into the S-ethyl ether.  The Specification as open to inspection under Sect. 91 relates to the manufacture of polymethine dyes containing a substituent at the central carbon atom of the polymethine chain, and comprises the use in sensitizing a silver halide emulsion of any unsymmetrical carbocyanine dye substituted at the central carbon atom of the trimethine chain; also of a symmetrical carbocyanine dye substituted at the central carbon atom of the trimethine chain by a propyl group.  It is stated that the latter dyes cannot be produced by use of an orthoacid ester in the known manner since orthobutyric acid esters are unknown.  This subject-matter does not appear in the Specification as accepted.