Patent GB-457450-A (GB)
Title: Manufacture of dyes and process for sensitising photographic silver halide emulsions
IPC: C09B23/02
Filed: 1935-05-24
Abstract: Cyanine dyes are prepared by condensing a quaternary alkyl salt of a heterocyclic base of the general formula <FORM:0457450/IV/1> wherein X stands for sulphur, oxygen or selenium, with an alkyl ester of an orthocarboxylic acid, diarylformamidine, b -ethoxyacrolein-acetal, or glutaconic aldehyde dianilide hydrochloride.  Unsymmetrical cyanine dyes are prepared by condensing the above-defined quaternary salt with a quinoline alkyliodide or with a molecular proportion of a diarylformamidine followed by condensing this condensation product with a quinaldine alkyliodide.  Styryl dyes are prepared by condensing the above-defined quaternary salt with a p-dialkylaminobenzaldehyde. The products have a high solubility in organic solvents and in water and have a strong sensitizing power when applied to photographic emulsions.  In examples dimethylthiodiazole ethiodide (made by heating the base with ethyl iodide) is condensed (a) in acetic anhydride with triethyl orthoformic acid to give a mixture which is resolved by fractional precipitation into a carbocyanine containing three methylthiodiazole rings and an unsubstituted carbocyanine; (b) in alcohol containing piperidine with p-dimethylaminobenzaldehyde; (c) in pyridine with triethyl ortho-acetic acid ester; (d) in pyridine with b -ethoxyacrolein acetal; (e) in alcohol containing sodium alcoholate with quinoline ethiodide; (f) with a molecular proportion of diphenylformamidine to give an intermediate which is condensed with quinaldine ethiodide in pyridine.  A further example illustrates the use of these products for sensitizing photographic emulsions. either by adding an alcoholic solution (0,1 per cent) to an uncast gelatine-bromide photographic emulsion or by bathing plates or films coated with gelatine-bromide emulsion in such solution, and in the examples sensitizing data of the products are furnished. The dyes wherein X is represented by oxygen sensitize to shorter wave lengths than the corresponding thio-dyes whereas when X is represented by selenium the dyes sensitize to longer wave-lengths than the corresponding thio-dyes.  Dimethylselenodiazole is prepared like the corresponding thiodiazole using phosphorus pentaselenide instead of the pentasulphide (cf. J. für Prak. Chem. 69, 145-160).  The Specification as open to inspection under Sect. 91 relates broadly to an improvement in the manufacture of dyes by condensing a quaternary alkyl salt of a heterocyclic base to form cyanine or styryl dyes consisting in the use as parent heterocyclic base of dimethyl-thiodiazole, -furodiazole or -selenodiazole; and to sensitizing photographic emulsions by incorporating therein a cyanine or styryl dye containing at least one ring of the structure <FORM:0457450/IV/2> wherein X stands for sulphur, oxygen or selenium, Y for alkyl and Z for halogen, methylsulphate, perchlorate or other anion.  Dyes also specified for use in this way are further formulated <FORM:0457450/IV/3> wherein X, Y and Z are as above, n stands for 0, 1, 2 or 3 and wherein one or more hydrogen atoms of the polymethine chain may be exchanged for alkyl.  This subject-matter does not appear in the Specification as accepted.  Reference has been directed by the Comptroller to Specification 425,609.