Patent GB-425417-A (GB)
Title: Process for sensitizing photographic emulsions
IPC: G03C1/20
Filed: 1933-09-14
Abstract: Sensitizers for silver halide emulsions are penta and heptacarbocyanine dyes in which the polymethine chain is unsubstituted and the benzene rings are substituted in each of the two positions p to the carbon atoms common to the benzene and heterocyclic rings.  The dyes correspond to the general formula <FORM:0425417/IV/1> wherein Y is S, Se, O, --CH=CH-- or CR2 (R being alkyl or aryl), R1 and R2 are alkyl, alkoxy, alkylthio or aryl, X is an acid radicle such as C1, Br, I, SO4.CH3 or ClO4, R3 is alkyl and n=2 or 3.  In place of separate substituents, R1 and R2 together may be a methylene-or ethylene-dioxy group.  Examples are given of (1) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - tetramethoxybenzothiopentacarbocyanine iodide obtained by boiling 2 - methyl - 5 : 6 - dimethoxybenzothiazole ethiodide with b  - ethoxy - acrolein - acetal in pyridine; (2) 1 : 1<1> - diethyl - 5 : 5<1> - dimethyl - 6 : 6<1> - diethoxybenzothiopentacarbocyanine iodide obtained as in example 1 starting from 2 : 6 - dimethyl - 5 - ethoxybenzothiazole ethiodide; (3) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - tetramethoxybenzothioheptacarbocyanine iodide obtained by boiling 2 - methyl - 5 : 6 - dimethoxybenzothiazole ethiodide with a - phenylamino - e  - phenylimino - a  : g  - pentadiene - hydrobromide; (4) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - tetraethoxybenzothioheptacarbocyanine iodide obtained as in (3) starting from 2 - methyl - 5 : 6 - diethoxybenzothiazole - ethiodide; (5) 1 : 1<1> - diethyl - 5 : 6 : 5<1> - tetraethoxybenzoselenoheptacarbocyanine iodide obtained by boiling 2 - methyl - 5 : 6 - diethoxybenzoselenazole with a  - (N - methyl - phenylamino) - e  - (N - methyl - phenylimino) - a  : g  - pentadiene hydrobromide in the presence of methylamine; (6) 1 : 1<1> - diethyl - 5 : 5<1> - dimeththio - 6 : 6<1> - dimethoxybenzothiopentacarbocyanine iodide obtained by boiling 2 - methyl - 5 - methoxy - 6 - meththiobenzothiazole ethiodide with b  - ethoxy - acrolein - acetal in pyridine; (7) 1 : 1<1> - diethyl - 5 : 5<1> - dimeththio - 6 : 6<1> - dimethoxybenzothioheptacarbocyanine iodide obtained by heating 2 - methyl - 5 - methoxy - 6 - meththiobenzothiazole ethiodide with a  - (N - methyl - phenylamino) - e  - (N - methyl - phenylimino) - a  - g  - pentadiene hydrobromide in the presence of pyridine; (8) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - bis - methylenedioxybenzothiopentacarbocyanine iodide obtained by boiling 2 - methyl - 5 : 6 - methylenedioxybenzothiazole ethiodide with b  - ethoxyacroleinacetal in pyridine; (9) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - bis - ethylenedioxybenzoselenopentacarbocyanine iodide obtained as in (8) starting from 2 - methyl - 5 : 6 - ethylenedioxybenzoselenazole ethiodide; (10) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - bis - methylenedioxybenzothioheptacarbocyanine iodide obtained by heating 2 - methyl - 5 : 6 - methylenedioxybenzothiazole ethiodide with a  - phenylamino - e  - phenylimino - a  : g  - pentadiene hydrobromide in the presence of piperidine and; (11) 1 : 1<1> - diethyl - 5 : 6 : 5<1> : 6<1> - bis - ethylenedioxybenzoselenoheptacarbocyanine iodide obtained by boiling 2 - methyl - 5 : 6 - ethylenedioxybenzoselenazole ethiodide with a  - phenylamino - e  - phenylimino - a  : g  - pentadiene hydrobromide in the presence of diethylamine.  For making 2 - methyl - 5 - methoxy - 6 - meththiobenzothiazole, 1 - chloro - 2 - methoxy - 4 - nitrobenzene is converted by sodium disulphide into 2 : 2<1> - dimethoxy - 4 : 4<1> - dinitrodiphenyl - 1 : 1<1> - disulphide which is dissolved in sodium hydrosulphide and treated with dimethylsulphate to give 1 - meththio - 2 - methoxy - 4 - nitrobenzene which is reduced to 1 - meththio - 2 - methoxy - 4 - aminobenzene which is converted into the thiazole.  Specification 418,745 is referred to.