Hydroquinone developer

Formaldehyde emission regulations, 15 776 Formaldehyde gas, 12 110 Formaldehyde-hydroquinone developers, 19 210... 

Fig. 5. Electron micrograph of two silver grains obtained by developing silver bromide grains in a distortionless hydroquinone developer.

The solvent action of sulfite on silver bromide and the resultant tendency to isolate latent image nuclei from the grain accounts for the failure of sulfite itself to act as a direct developer in spite of the autocatalytic character of its reduction of silver ion. The active nuclei simply are isolated from the grain before development gets under way. The same phenomenon enters to prevent sulfite-containing hydroquinone solutions of low pH (e.g., 8.5) from developing readily even though the thermodynamic conditions are suitable for reaction and the hydroquinone develops readily at the same pH when sulfite is absent. 

In a modification of the process the sensitized layers are arranged as before but nonwandering couplers are incorporated into the respective layers during manufacture of the film. This means that, after the hydroquinone development has been carried out, the differently coloured images can be formed in one common developer solution. Silver and silver halide are removed as previously. 

Uses Hardening bath (10% solution). In connection with hydroquinone developer, yields negatives of great contrast useful for developing litho film. A small amount prevents swelling of gelatin in warm solutions. Also useful as a preservative. 

At temperatures below 50F/10C hydroquinone developers are inactive. It is extremely susceptible to the action of bromide. When compounded with alkali carbonates it gives a slow-working but high contrast developer. With caustic alkali (e.g., sodium hydroxide) its action is very rapid, with the highest possible contrast. For this reason, it is the most widely used developer for technical applications, especially in process work where the highest attainable contrast is essential. In the presence of caustic alkali (i.e., high pH) it is not temperature-sensitive and can be used for low-temperature developing. Hydroquinone developers keep well and are slowly exhausted. 

Uses A small amount in pyro and hydroquinone developers tends to lower fog and give greater density. 

Uses Toning baths retarder in hydroquinone developer used to buffer acidity of acid solutions. Notes Keep in a tightly sealed bottle in a cool place. 

These reactions involve proton and electron transfer and kinetic data suggest that the mechanism involves a protonated intermediate followed by base-catalyzed deprotonation of the ring [32]. In black-and-white developers the amount of sulfite present is usually very high at about 60 g L of sodium sulfite (0.5 m), and almost all the oxidized developer formed is immediately removed from the reaction site. (At low sulfite levels the effects of accumulated oxidation products can have a significant effect on the development rate, particularly for hydroquinone developers see the section on Lith development ). In the case of hydroquinone the reaction with sulfite is similar to that of p-phenylenediamine (Eq. (22)). 

Electochemical measurements by Jaenicke and co-workers [56] indicate two possible mechanisms by which superadditivity could arise. In the first, a developer showing irreversible oxidation becomes reversible in the presence of a second developing agent. In the second, when the mixed potential is in the limiting current region of the anodic reaction, superadditivity occurs if the limiting current rises because the number of electrons delivered per molecule of a first developer, for example hydroquinone, is increased by the addition of a second developer, such as Phenidone. This could happen with hydroquinone development in the presence of sulfite because the reaction product, hydroquinone monosulfonate, is a poor developer by itself but in the presence of Phenidone it is activated. 

Predicting Time, temperature, and solution concentration are all important factors in the developing process. What would be the consequence of leaving the film too long in the hydroquinone developer (Hint the developer is a reducing agent.)... 

Rate constants of the process and the nuclearity-redox potential correlation will be compared with corresponding data obtained in another environment, particularly when a surfactant or an associated ligand is present. The complete analysis of the autocatalytic transfer mechanism will also be compared with the photographic process of electron transfer from hydroquinone developer to clusters supported on silver bromide. 

Texter, J., Hydroquinone development acceleration by tri-azolium thiolates, J. Photogr. Sci, 40, 83-88 (1992). 

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