GB776050A - Improvements in carbocyanine dyes, processes of preparing them and photographic emulsions containing them - Google Patents

Abstract

1 - Ethyl - 5 - ethylcarbamyl - 2 - methyl benzimidazole is prepared by heating N-ethyl-4-ethylamino-3-nitrobenzamide in a mixture of glacial acetic acid and acetic anhydride and adding zinc dust. The reaction mixture is made alkaline with caustic soda. 5-Acetyl-1-ethyl-2-methyl benzimidazole and 5-bromo-1-ethyl-2-methyl benzimidazole are similarly prepared. The benzimidazole bases are quaternized by refluxing with ethyl iodide. The positions of the ethylcarbamyl, acetyl or bromine substituents may be varied by selecting the appropriate starting materials. N - Ethyl - 4 - ethylamino - 3 - nitrobenzamide is prepared by shaking methyl 4-chloro-3-nitrobenzoate with excess ethylamine. 4-Ethylamino-3-nitro-acetophenone is similarly prepared from 4 - chloro - 3 - nitro - acetophenone. The ethylamine may be replaced by other amines such as allylamine, n-propylamine or aniline and the corresponding 1-substituted benzimidazoles prepared as described above. Specification 776,049 [Group XX], is referred to.ALSO:Symmetrical carbocyanine dyes having benzimidazole nuclei substituted by acetyl, alkyl carbamyl or bromine groups are prepared by condensing a compound of the formula:- <FORM:0776050/IV(b)/1> wherein R is an alkyl allyl, substituted alkyl or aryl group R1 is an alkyl, allyl or substituted alkyl group, R3 is acetyl, alkyl carbamyl or bromine and X is an anion, with a chloral alcoholate. Unsymmetrical carbocyanine dyes are prepared by condensing a benzimidazole compound of the above formula with a compound of the formula:- <FORM:0776050/IV(b)/2> wherein R2 is an alkyl, allyl or substituted alkyl group, R4 is an acyl group, R5 is an aryl group, X1 is an anion, n is 0 or 1 and Z completes a heterocyclic nucleus. R, R1 and R2 may be methyl, ethyl, n-propyl, n-butyl, or carbethoxymethyl and a list of nuclei which Z may complete is given. In the examples Z completes a benzoxazole or 3 : 3 - dimethyl indolenine nucleus. Specification 776,049 [Group XX] is referred to.