Patent GB-405309-A (GB)
Title: Manufacture of dyes
IPC: C09B23/02
Filed: 1932-07-28
Abstract: In the manufacture of carbocyanines, useful for sensitising photographic silver halide emulsions, heterocyclic bases are used as starting material which contain a thiazole ring, or an oxygen or selenium analogue, having in the 2-position an aralkyl group or an alkyl group with at least two carbon atoms.  These bases are condensed, for example with aliphatic ortho esters according to known methods whereby carbocyanines are obtained in which an alkyl or aryl group is present in the a  or lateral position in the tri-methine chain, and possibly an alkyl group in the b  or central position. The said bases containing an alkyl group with at least two carbon atoms in the 2-position may also be used for the preparation by known methods of iso and pseudo cyanines, which thereby contain an alkyl group attached to the methine carbon atom.  In examples: (1) 2-ethylbenzthiazole ethyliodide is condensed with ethyl o-formate to give 1 : 1<1>-diethylbenzthio-a  : a <1>-dimethylcarbocyanine iodide: (2) 1-ethyl-a -naphthothiazole diethylsulphate is condensed with ethyl o-acetate to give 1 : 1<1>-diethyl-a -naphthothio-a  : b  : a <1>-trimethyl-carbocyanine iodide: (3) 1-propyl-a -naphthothiazole diethylsulphate is condensed with ethyl-o-formate: (4) 2-ethylbenzselenazole dimethylsulphate is condensed with ethyl-o-acetate or propionate: (5) 2 - ethyl - 5 - ethoxybenzselenazole - dimethylsulphate is condensed with ethyl-o-formate: (6) 2-ethylbenzselenazole methyliodide is condensed with 2-iodoquinoline ethyliodide or its 6-methyl derivative: (7) 2-ethylbenzthioazole methyliodide is condensed with 2-iodo-6-methylquinoline ethyliodide.  The halides, perchlorates and nitrates of the dyestuffs are mentioned.  2-Ethylbenzselenazole may be prepared by distilling the mixture obtained by boiling o : o<1>-diaminodiphenyl diselenide with propionic anhydride and zinc dust and adding alkali.  2-Ethyl-5-Ethoxybenzselenazole may similarly be prepared from p : p<1>-diethoxy-o : o<1>-diaminodiphenyldiselenide which is obtainable from 1-amino-2-nitro-4-ethoxybenzene by diazotising, treating with potassium selenocyanide and reducing the resulting p : p<1>-diethoxy-o : o<1>-dinitrodiphenyldiselenide. 1-Ethyl-a -naphthothiazole may be prepared by fusing 1-amino-a -naphthothiazole with caustic potash and heating the resulting potassium salt of 1-mercapto-2-naphthylamine with propionic anhydride.  1-n-Propyl-a -naphthothiazole may similarly be prepared. 2-Iodo-6-methylquinoline ethyl iodide may be prepared by oxidising p-toluquinoline diethylsulphate with potassium ferricyanide to 1-ethyl-6-methylquinolone and treating the latter with phosphorus pentachloride to form the 2-chlor derivative which yields the corresponding 2-iodo-6-methylquinoline ethyl iodide by heating in a sealed tube with ethyl iodide.  Specifications 345,735 and 347,141 are referred to.  The Specification as open to inspection under Sect. 91 comprises also the production and use as sensitisers of cyanine dyes of any type containing an alkyl or aryl group in at least one of the a -positions of the polymethine chain or in the methine group. In a further example, 1 : 1<1>-dimethyl-a  : a -dimethyldibenzthiopentacarbocyanine iodide is prepared from 2-ethylbenzthiazole methyliodide and b -ethoxyacroleinacetal. Bases containing the group =C(CH3)2 or tellurium may also be used. Heptacarbocyanines are mentioned, and in the case of pseudo cyanines, the methine hydrogen may be replaced by aryl. This subject-matter does not appear in the Specification as accepted.