Pyrogallol

Colorless, shiny leaves or needles

Fixed

1.45 g · cm -3

131-135 ° C

309 ° C

2-4 hPa (140 ° C)

9.01

• Good in water ( 400 g · l-1 at 20 ° C)
• Soluble in ethanol and diethyl ether
• Poorly in chloroform and benzene

1.561 (134 ° C)

Attention

780 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Pyrogallol ( 1,2,3- trihydroxybenzene ) is a derivative of benzene, a trivalent phenol with three vicinal hydroxyl groups. The other two isomers of phloroglucinol (1,3,5- trihydroxybenzene ) and hydroxyhydroquinone (1,2,4- trihydroxybenzene ).

History

Pyrogallol was first established in 1786 by Carl Wilhelm Scheele by heating gallic acid, characterized and named. The name derives from the Greek pyr = fire and gallol of gallic acid; -ol refers to the hydroxy (OH) groups, and is indicative of the manufacturing method.

Extraction / representation

Pyrogallol can be made most easily by pyrolysis of gallic acid decarboxylation.

It is also formed in the decomposition of tannins.

Properties

Pyrogallol is in a pure state of white crystalline needles, but the color on the air fast gray - brown. It is a strong reducing agent and absorbed eagerly in alkaline solution oxygen from the air; it complexed metal ions (e.g. Fe3 , a blue color ). Upon prolonged standing in air ( especially in alkaline solution ) is pyrogallol about by oxidation into carbon dioxide, acetic acid, purpurogallin ( Trihydroxybenztropolon ) and other decomposition products; the solution turns dark brown then. The aqueous solutions react gradually acidic due to this decomposition, hence comes the name pyrogallol, which is not a true name for the pure substance.

Use

It has been used for the quantitative ( volume) oxygen analysis and is used in holography still use. After it was rarely used as a photographic developing agent for a long time, developers are again popular with pyrogallol share today. Partial pyrogallol is used in addition to BHT as stabilizer for substances such as diethyl ether, subject to the auto-oxidation by atmospheric oxygen.

Proof

For qualitative analytical detection arises in the bromination with potassium bromide and bromine, the dibromo derivative, which has a melting point of 158 ° C.

Reactions

Carboxylation of pyrogallol by a Kolbe-Schmitt reaction leads to the pyrogallol - 4-carboxylic acid.

Safety

Pyrogallol is harmful. It will also gradually absorbed through the skin. In animal experiments, as well as when trying to change the DNA of human cells could be detected.