Pyrogallol

Pyrogallol is a benzene derivative with three adjacent hydroxyl groups, formula C₆H₃(OH)₃. It readily oxidizes in air, giving it uses in chemical analysis, photography, and gas absorption.

Autoxidation: The spontaneous oxidation of a substance by molecular oxygen without an added oxidizing agent. Pyrogallol consumes oxygen through rapid autoxidation, especially in alkaline solution.
Gas analysis: The measurement of the composition of a gas mixture using chemical or instrumental methods. Alkaline pyrogallol absorbs oxygen, allowing its amount in a gas sample to be measured.
Benzene: An aromatic hydrocarbon with six carbon atoms arranged in a planar ring. Pyrogallol’s six-carbon aromatic framework is a benzene ring.
Carl Wilhelm Scheele: A Swedish-German chemist known for discoveries in eighteenth-century experimental chemistry. Scheele isolated pyrogallol by heating gallic acid, the preparation reflected in its name.
Reactive oxygen species: Reactive oxygen-containing molecules and radicals formed in processes such as oxidation and metabolism. Pyrogallol autoxidation can generate superoxide and hydrogen peroxide.
Orsat apparatus: A manual gas-analysis instrument that measures constituents of combustion gases by selective absorption. Its pipettes can use alkaline pyrogallol to remove oxygen from a measured gas sample.
Phenol: An aromatic compound in which a hydroxyl group is bonded directly to a benzene ring. Pyrogallol is a triphenol, with three phenolic hydroxyl groups on one ring.
Gallic acid: A naturally occurring phenolic acid found in plants and in hydrolysable tannins. Heating gallic acid can remove carbon dioxide and yield pyrogallol.
Alkaline solution: A water-based solution with a pH greater than seven. Alkali accelerates pyrogallol oxidation and enables its use as an oxygen absorbent.
Photographic developer: A chemical solution that converts exposed silver halide crystals in film or paper into metallic silver. Pyrogallol can develop photographic images because it reduces exposed silver halide.

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