Pyrazolone dyes

Pyrazolone dyes are particularly versatile yellow chromophores the yellow dye developer used in Polacolor, the first instant color film, was based on a pyrazolone dye. The stmctures of the three Polacolor dyes are shown in Figure 3. The study of azo dyes derived from 4-substituted 1-naphthols led to the chromophore used in the Polacolor magenta dye developer. The Polacolor cyan dye developer contained a 1,4,5,8-tetra-substituted anthraquinone as chromophore (20). 

Pyrazoles, 13 599 Pyrazolinone couplers, 19 254-255 Pyrazolo-(3,2,-c)-5-triazole couplers, 19 256 Pyrazolobenzimidazole couplers, 19 256 Pyrazolone dyes, 19 285 Pyrazolone Orange, 19 435 pigment for plastics, 7 367t Pyrazolone reds, 19 437 Pyrazolones, 9 283 13 599... 

The situation in the pyrazolone-azo dye series is more complex. In contrast to former assumptions the dyes are inaccurately described as azo compounds and in fact exist exclusively in a tautomeric phenylhydrazone form. The simple pyrazolone dye (116 R=H) absorbs at 398 nm in ethanol (67BCJ1239). In this instance the pyrazolone heterocyclic ring... 

Technical Observations. The manufacture of pyrazolone dyes is relatively simple. The arylhydrazine condensations are usually run in enameled vessels to minimize losses of expensive materials. Nothing particularly new is involved in the diazotization and coupling reactions. 

This is the simplest member of the pyrazolone dyes which are prepared in two ways (a) from dihydroxytartaric acid and phenylhy-drazine (tartrazines), and (b) from phenylmethylpyrazolones by coupling with diazo compounds. The second method is simpler and has largely displaced the older, first method. The pyrazolone is prepared from a given phenylhydrazine (e.g., phenylhydrazinesulfonic acid, page 128) and acetoacetic ester, and coupled with diazotized aniline ... 

Sulfonation of pritnuline-like color bases by the baking process yields sulfonic acids whose azo dye derivatives are more fast to light than those from sulfonic acids prepared in the ordinary way. It is assumed that in the baking process, the sulfo group enters ortho to the amino group, and that this increases the light fastness. This same principle was mentioned in connection with the pyrazolone dyes. 

Comments tartrazine is a monoazo, or pyrazolone, dye. It is used to improve the appearance of a product and to impart a distinctive coloring for identification purposes. 

The pyrazolone dye 16 may serve as an example of the use of pyrazolones as couplers in color photography, which react with the developer (e.g., N,N-diethyl-p-phenylenediamine) in an oxidative coupling process during the chromogenic development. 

A further example of pyrazolone dye is Acid Red 38. This dye is the chromium complex of the azo compound made by coupling diazotized 2-amino-5-nitrophenol with meta-(3-methyl-5-oxo-2-pyrazolin-l-yl)-benzene-sulfonamide. It is used as a dye for wool and nylon. Acid Red 38 has one advantage over dyes such as Mordant Black 17 in that the dyer does not have to form the chromium complex by a separate operation during the dyeing process. 

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