PYROGALLOL, or Pyrogallic Acid, a trioxybenzene, C 6 H 3 (OH) 3 (1: 2: 3), prepared by Scheele in 1786 by heating gallic acid, C 6 H 2 (OH) 3 CO 2 H.
Pyrogallol dimethyl ether is found in beechwood tar.
Pyrogallol has antiseptic properties and is employed medicinally in the treatment of psoriasis.
Eugallol, or monacetyl pyrogallol and lenigallol, or triacetyl pyrogallol, are also used.
This may be effected by burning phosphorus in a confined volume of air, by the action of an alkaline solution of pyrogallol on air, by passing air over heated copper, or by the action of copper on air in the presence of ammoniacal solutions.
Anthragallol is synthetically prepared by the condensation of benAoic and gallic acids with sulphuric acid OH i [[Cooh + I 10h - 2h20+ Hooc /Oh]] or from pyrogallol and phthalic anhydride in the presence of sulphuric acid or zinc chloride.
It melts at about 200° C., and at 210° to 255° it is resolved into carbon dioxide and pyrogallol, C 6 H 3 (OH) 3.
An alkaline solution of pyrogallol is also used; this solution rapidly absorbs oxygen, becoming black in colour, and it is necessary to prepare the solution immediately before use.