Color couplers

Aromatic azapentalenes feature in a number of patents dealing with color couplers, sensitizing dyes, and emulsion stabilizers (see also Section IV,C,4,b). Derivatives of pyrazolo[l,5-[Pg.312]

Figure 28-12 Schematic changes in the development of a color film exposed to green light. The color couplers are present in the original sensitized layers.

A different color coupler is used for each layer of the emulsion and, although the complete color picture is formed in this step, the film is coal black because of the metallic silver produced at the same time. The silver then is oxidized to silver bromide with dichroinate solution containing bromide ion and removed with thiosulfate solution. The final image thus contains no silver. 

Such dyes often are called azomethines. The nature of the exact color couplers used in color film is not well publicized. It is important that the couplers not diffuse out of the layers where they belong and, for this reason, insolubilizing substituent groups are attached to strategic positions on the color couplers. 

A limited set of phenylenediamine color developers are used. Kodak s CD-3, CD-4, and CD-6 (26-28) are the principle color developers used today [31], They are directly incorporated into the alkaline processing fluid. The methyl group in the 2-position is important for preventing side reactions and enhancing the formation of the desired dye. The phenylenediamine undergoes a two-electron oxidation to quinonediimine, which then reacts with the color couplers to form the desired chromophores [32],... 

In recent years a great deal of research on 5-imino-3-pyrazoli-dinones has been done because of their use as color couplers in color... 

The pyrazolinones and pyrazolidinones are extensively employed in photography as color couplers, sensitizers, supersensitizers, developers and antihalation agents. A number of pyrazolinones which have been prepared for use as sensitizers are listed in Tables LI and LIL... 

U40.ii42.i247.i684 Weissberger and Edens1593 have reported very complex amides which are useful as color couplers, but are so complex that they are listed in none of the tables. In the color photography process employing the 2-pyrazolin-5-one in solution in the developer, low... 

Although by far the majority of 2-pyrazolin-5-ones used as color couplers have no substituent at C-4, this is not a necessary condition. 4,4 -Bis(2-pyrazolin-5-ones) can be used for this purpose since the 4-substituents can be eliminated and an azomethine dye formed. Such couplers may offer certain advantages. It is claimed that they are more stable and also they make it possible to form two azomethine dyes if the two portions of the molecule are different. Weissberger, Vittum and Porter1540,1603 have patented a number of 4,4 -arylidenebis(2-pyra-zolin-5-ones) for use as color couplers. Gluck580 has suggested 4,4 -bis-(2-pyrazolin-5-ones) linked by sulfur which he prepared. 

Another approach to prevention of diffusion of color couplers has been the incorporation of 2-pyrazolin-5-ones into some type of polymer. 

In many photographic processes it has been found advantageous to use a colored coupler. In these processes a 4-arylazo-2-pyrazolin-5-one is the coupler and it reacts with a developer as shown in eq. 272 (p. 138).1539 This results in the formation of an azomethine dye which counteracts the overlapping absorption of the negative image dyes present and leads to improved color reproduction. These compounds usually have a negative substituent at N-l 1058,1305 as this enhances the... 

Aryliminopyrazol-3-ones are widely employed as color couplers in photography. In an attempt to synthesize (E/Z)-4-phenyliminopyrazol-3-one 345 by heating... 

Oxidation dyes are often referred to as permanent hair dyes and are the most important of the commercial hair dyes. Permanent hair dyes generally consist of p-diamines and p-aminophenols that are oxidized by hydrogen peroxide to active intermediates [3]. These active intermediates then react inside the hair with color couplers to provide shampoo-resistant hair dyes. 

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