Gallic acid

3,4,5- trihydroxybenzoic acid, pyrogallol - 5-carboxylic acid

Yellowish needles

Fixed

1.69 g · cm -3

253 ° C ( decomposition)

3.13

• Poorly in cold water ( 11.9 g · l-1 at 20 ° C), slightly in warm water
• Insoluble in ethanol, acetone and glycerol
• Insoluble in benzene, chloroform and petroleum ether

Attention

5000 mg · kg -1 ( LD50, rabbit, oral)

Template: Infobox chemical / molecular formula search available

Gallic acid (3,4,5- trihydroxybenzoic acid ) is an aromatic compound which is derived both from the benzoic acid and the pyrogallol ( 1,2,3- trihydroxybenzene ). The structure consists of a benzene ring with an attached carboxy (-COOH ), and three hydroxyl groups (-OH) as a substituent. It belongs to the group of Trihydroxybenzoesäuren, its salts hot gallates.

History

Gallic acid was first described by Carl Wilhelm Scheele. As a natural product of plant secondary metabolism, it is the most important parent compound of the aromatic compounds in petroleum.

Occurrence

Gallic acid is the building block of plant Gerbstoffgruppe the gallotannins and comes, for example, very rich in oak bark and galls before. Green tea contains compared to black tea ten times the content of gallic acid, gallic acid and twice as much as oolong tea.

Synthesis

In the industrial preparation of gallic acid most molds are used, wherein the enzyme tannase is formed. Tannase decomposed tannins in gallic acid and sugar. Gallic acid can also be obtained from aqueous extracts of galls or by hydrolytic cleavage with dilute acids.

Properties

When heating gallic acid is formed under elimination of carbon dioxide ( decarboxylation) the pyrogallol ( 1,2,3- trihydroxy ).

Use

Gallic acid is used for the production of iron gall inks (formerly ), antioxidants in food, sunscreen and dyes ( eg Anthrazenbraun, Gallaminblau, Gallozyanin, Rufigallussäure ).