Cyanine dyestuff

In two patents,the preparation of thioether-substituted selena-zoles of the general formula (6) have been described. These are stated to be formed by reaction of halogenoketothioethers with selenoamide components selenoacetamide, selenobenzamide, and A -ethylseleno-urea are given as examples. The resulting selenazoles were not further characterized. They are stated to be starting materials for the preparation of cyanine dyestuffs which are useful photographically. 

Dimethylamino)-benzaldehyde reacts in acidic medium, e.g. with the indole ring of cyclopiazione or ergot alkaloids and forms a cyanin dyestuff by electrophilic substitution in the 2-position followed by the elimination of water [12, 17]. 

The substitution of two or three hydrogen atoms of methane by six-membered nitrogen heterocycles, like pyridine, quinoline, or benzoquinoline, leads to a class of compounds which we call quinolylmethanes, as its representatives are in structure as well as in their chemical and physical properties similar to di-(2-quinolyl)methane, the compound prepared first.1 Substitution of the central —CH2— (or =CH—) bridge by —NH— (or =N—) leads to the corresponding quinolylamines. Quinolylmethanes and quinolylamines are the fundamental substances of many cyanine dyestuffs. 

On quaternization with alkyl halides, 2-quinolyl-4-quinolyl-methanes yield isocyanines and di-(4-quinolyl)methanes the corresponding cyanines. Quinolylamines give azacyanines in an analogous way. Since cyanine dyestuffs are readily prepared by condensation of the A-alkyl quaternary compounds39,40 of quinolylmethanes and -amines, by reactions analogous to those described in Section II, A, 1, the method of preparation involving alkylation of the parent compounds is of little practical use. 

For the cyanine dyestuffs, a characteristic correlation exists between basicity, the sterically induced twisting of parts of the molecule out of the plane, and the electronic excitation energy.42"45... 

The reductive cyclization of 2-nitrophenylselenoacetic acid (168) with iron and acetic acid yields 2/7-l,4-benzoselenazin-3(4//)-one (169) (Equation (38)) <30JPR336>. This product is also available by the annulation of zinc di(2-aminophenyl)selenide (170) through reaction with chloroacetic acid and hydrogen chloride in ethanol. When treated with phosphorus pentasulfide the corresponding thione (171) is formed, and this, with bromoacetone and perchloric acid, affords 1-methyl-thiazolo[2,3-c]-l,4-benzoselenazium perchlorate (172), the basis of some cyanine dyestuffs... 

This nucleus has also been referred to as 4,5-quinoxalinoimidazole and imidazolo-5, 4 2,3-quinoxaline. Most of the reported derivatives of this ring system are cyanine dyestuffs and may be named accordingly. For example, Chemical Abstracts indexes compound SO as an imidazo[4,5-h]quinoxalinocarbocyanine, as well as by using more systematic nomenclature. Similarly 51 may also be called an imidazo[4,5-h]quinoxalino-indocarbocyanine, and compound 52 is referred to as an imidazo[4,5-b ]quinoxalinothiacarbocyanine. 

Ogata, T. Cyanine dyestuffs. IV. Pentamethine- and heptamethine-cyanines. Proc. Imperial Acad. 1932, 8, 421 23 Chem. Abstr. 1933, 27, 10023. 

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