Pyrogallol is an organic compound with the formula C 6 H 3 (OH) 3 . It is a soluble solid in water although the sample is usually brownish because of its sensitivity to oxygen. This is one of the three isomeric benzenetriol.
Video Pyrogallol
Produksi, kejadian, reaksi
It was produced in the way first prepared by Scheele (1786): heating the acid error. Currently the gallic acid is obtained from tannins. Heating induces decarboxylation:
Because tannins are expensive, many alternative routes have been designed. An alternative preparation involves the treatment of para-chlorophenoldisulphonic acid with potassium hydroxide, a variant on a time-honored route for the phenol of sulfonic acid.
Aquiline plant Myriophyllum spicatum produces pirogallic acid.
When in an alkaline solution, it absorbs oxygen from the air, turning brown from a colorless solution. It can be used in this way to calculate the amount of oxygen in the air, especially through the use of the Orsat apparatus.
Maps Pyrogallol
Usage
One can find its use in hair dyes, dyeing of suturing materials and for the absorption of oxygen in gas analysis. It also has antiseptic properties. Pyrogallol is also used as a development agent in black and white developers, but its use is largely historical except for special purpose applications. (Hydroquinone is more commonly used today.). It is also used in the inert gas insulation of the gas mixture, which requires the absorption of oxygen from the mixture.
Use in photography
Although popular photography development agencies in the 19th and early 20th centuries, pyrogallol was largely disliked around the 1920s, although it is still used by some famous photographers including Edward Weston. In those days it had a reputation for erratic and unreliable behavior, due to its propensity for oxidation. It experienced a revival beginning in the 1980s due in large part to the experimental efforts of Gordon Hutchings and John Wimberley. Hutchings spent more than a decade working on pyrogallol formulas, eventually producing what he called the PMK (for the main ingredient, pyrogallol, Metol, and Kodalk [Kodak trade name for sodium metaborate]). This formulation solves the problem of consistency, and Hutchings finds that the interaction between greenish stains given to the film by the pyro developers and the color sensitivity of modern contrast-color photographic paper gives effect from extreme compensation developers. From 1969 to 1977, Wimberley experimented with Pyrogallol's development agency. He published the formula for WD2D in 1977 at Petersons Photographic.
PMK and other modern piro formulations are now used by many black and white photographers.
The Movie Developing Cookbook has an example.
Security
Pyrogallol usage, eg. in hair dye formulations, decreased due to concerns about its toxicity. LD50 (oral, rat) is 300 mg/kg.
See also
- Error acid
- Catechol
- Syringol
- Gallacetophenone (2,3,4-trihydroxyacetophenone)
References
Source of the article : Wikipedia
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