Formazans selenazole

Selenazole formazans, dyes, photography and color industry, 274 from selenazole benzylidenehydrazones. 254... 

Bulka et al.,22 during the attempted preparation of selenazole formazans, found that the hydrazones of the selenazoles with unsubstituted 5-positions reacted with diazonium salts to give 5-azo derivatives preferentially. Thus coupling 2-benzylidenehydrazino-4-phenyl-selenazole with diazotized o-phenetidine afforded two compounds that could be separated chromatographically on aluminum oxide. The main product (67%) was 2-benzylidenehydrazino-4-phenyl-5-(o-ethoxybenzeneazo) selenazole (7), which formed ruby red prisms with a green surface sheen, mp 206°C.29 The desired formazan formed the minor product (see Section II,B,6). 

Bulka et al. (43) have demonstrated the electrophilic reactivity of selenazoles possessing an hydrazonc in the 2-position and nonsubstituted in the 5-position toward diazonium salt to give 5-phenylazo derivatives preferentially. For example, the main product of the coupling of 2-benzylidene hydrazino-4-phenylselenazole with diazo-o-phenetidine is the 5-(o-ethoxyphenylazo)-selenazole (Scheme 371 ruby red prisms, m.p. 206°C. yield 67"o). A formazan is obtained as by-product. (See Section III.6) (43). 

Hydrazono-5-(p-dialkylaminophenylimino)seienazoles, pyrazolone azomethin selenazoles, quinoid dyes, and formazans are other important dyes used in photography and the color industry (cf. previous sections). 

Despite the inconveniences, a certain number of studies have been carried out, particularly concerning dyes containing azomethine groups. Such as hydrazones, pyrazolones, formazans, and selenazoles quinoids. Saturated heterocycles, that is, selenazolines and selenazolidines. have also been tackled. Selenium derivatives for pharmacological or physiological applications are little developed by comparison with their thiazole homologs. 

With the synthesis of the benzylidene hydrazones of selenazoles, it was possible to prepare formazans containing a selenazole ring. Of the compounds already described (Section I,C,1), 2-benzylidene-hydrazino-4,5-diphenyl- and 2-benzylidenehydrazino-4-methyl-5-carb-ethoxy-selenazole were used to couple with diazonium salts in order... 

Whereas reaction of hydrazones disubstituted in the 4,5-position of the selenazole rings with diazotized arylamines only gives formazans, compounds unsubstituted in the 5-position can be attacked there by the diazonium cation. In fact, the azo coupling in this position is decidedly quicker reaction of 5-benzylidenehydrazino-4-phenyl-... 

Tetrazolium selenazole salts (perbromides). preparation, by dehydrogenation of formazans, 255... 

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