Formazans special

Guanyl hydrazones (18) react with diazonium salts to yield a special class of formazans called guanazyls, e.g., 19 (Eq. 1).20 22 The reaction is... 

The earliest oxidations were effected with nitrous fumes and later with mercuric oxide and isoamyl nitrite.74 Lead tetraacetate in acetic acid is in many cases the reagent of choice, but the removal of by-products can present some difficulties.75 IV-Haloimides and amides in alcoholic solutions have been reported to yield essentially pure tetrazolium salts76 and have been found specially useful in the preparation of heteroaryl-substituted tetrazolium salt.77,78 The novel formazans 49 have been successfully oxidized to 50 using 7V-chloro succinimide (Eq. II).79 tert-Butyl hypo-... 

Verdrazyls, e.g., 210, are a class of cyclic free radicals, with characteristic ESR spectra and intense colors. They represent a special case of oxidation of formazans and can be obtained from the methylation of and simultaneous or subsequent dehydrogenation of formazans.359-361 Ver-... 

A special process for the production of coppered l,5-bis(2-hydroxyphenyl)-formazans 32 is based on the demethylative copperization of 1,5-bis(2-methoxy-phenyl)formazans [63], The method involves heating for a short time in pyridine, formamide, or dimethylformamide. 

Special Processes and Development Trends [36, 37], Many attempts have been made to remedy the weak points of the reactive dyeing system. Lightfastness could be significantly improved over a wide range of shades by development of effective chromophores (e g., triphenodioxazine and copper formazan for blues). However, in the red range, reactive dyes are still inferior in lightfastness to vat and naphthol dyes. 

The reaction mechanism of formazan formation has been studied by many researchers. The fundamental work of Busch and his coworkers and the studies by Hiinig and Boes, and by Hauptmann and Perissd, merit special mention. A host of other authors have endeavored to widen the sphere of application of the formazan reaction, and have extended it successfully to the 4,4-iV-diarylsemicarbazonesi and guanylhydrazones, -i respectively. 

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