Patent GB-378870-A (GB)
Title: Improvements in and relating to the manufacture of light-sensitive photographic materials
IPC: C09B23/06
Filed: 1931-03-12
Abstract: Thiocarbocyanines are prepared by condensing a quaternary salt of a 2-methyl-b -naphthothiazole or a 1-methyl-a -naphthothiazole with an orthocarboxylic acid ester having an alkyl, aralkyl, or aryl group linked directly to the carboxy carbon atom.  The preparation of 8-methyl-2.2<1> - dialkyl - 5.6 : 5<1>.6<1> - dibenzothio - carbocyanine by condensation of a 1-methyl-a -naphthothiazole quaternary salt with an ester of orthoacetic acid ester is excluded. An excess of the orthocarboxylic acid ester is preferably employed. In examples, (1) 2-methyl-b -naphthothiazole is condensed with ethyl-p-toluenesulphonate and the resulting quaternary salt condensed with two mols. of triethyl orthoacetate in pyridine; ammonium bromide is then added to give 8-methyl-2.2<1>-diethyl-3.4 : 3<1>.4<1>-dibenzothiocarbocyanine bromide; if methyl-p-toluenesulphonate be employed instead of the corresponding ethyl body 2.2<1>.8-trimethyl - 3.4 : 3<1>.4<1> - dibenzothiocarbocyanine bromide results; the acid radicle can also be changed: (2) 2-methyl-b -naphthothiazole ethyl-p-toluenesulphonate is condensed with 2 mols. of trimethyl orthopropionate in dry pyridine and a hot solution of potassium iodide added to give 2.2<1>.8-triethyl-3.4 : 3<1>.4<1> dibenzothiocarbocyanine iodide: (3) 2-methyl-b -naphthothiazole methyl p-toluenesulphonate is condensed with 2 mols. of methyldiethyl orthoisocaproate in dry pyridine, and potassium iodide added to give 2.2<1>-dimethyl-8-isoamyl-3.4 : 3<1>.4<1>-dibenzothiocarbocyanine iodide.  The preparation of other 8-substituted derivatives and of the corresponding dyes from 1-methyl-a -naphthothiazole proceeds on similar lines.  The thiazoles may be substituted in the fused-on benzene ring; thus 1-amino-4-ethoxynaphthalene, 1-amino-4-methoxynaphthalene, or 2-amino-7-methoxynaphthalene or acetyl derivatives of these may be treated in the known manner to produce a m -methylnaphthothiazole, and a quaternary salt of the latter, for example of a m -methyl-4-ethoxynaphthothiazole, is then condensed with an orthocarboxylic acid ester.  Dyes in which the alkyl groups in the 2.2<1>-positions are dissimilar are obtained by treating a mixture of two quaternary salts of the m -methylnaphthothiazole whereby a mixture of products is obtained, one constituent of which contains the desired dissimilar alkyl substituents.  Orthocarboxylic acid esters other than orthoformic esters are prepared by dissolving the corresponding acid nitrile in dry ethyl ether together with a dry alcohol, such as methyl or ethyl alcohol, and passing in dry hydrochloric acid gas.  The imino-ether hydrochloride separates, and is washed and dried prior to treatment with more dry alcohol.  The orthocarboxylic acid ester so formed is distilled over under reduced pressure. Thus trimethyl orthopropionate is derived from propionitrile by using methyl alcohol in each stage, trimethyl orthophenylacetate from benzyl cyanide, trimethyl-ortho-g -phenoxybutyrate from g -phenoxybutyronitrile, triethyl-orthobenzoate from benzonitrile, trimethyl ortho-p-toluate from p-tolunitrile. Mixed esters may be obtained by employing two different alcohols in the two stages of the preparation; thus isocapronitrile may first be converted to isocaproiminomethylether hydrochloride by the joint action of methyl alcohol and hydrochloric acid gas, and then by further treatment with ethyl alcohol methyldiethyl orthoisocaproate is obtained.  Specification 378,885 also is referred to.