Gallic acid

Structural formula
General
Surname	Gallic acid
other names	3,4,5-trihydroxybenzoic acid; Pyrogallol-5-carboxylic acid; GALLIC ACID ( INCI ) ;
Molecular formula	C 7 H 6 O 5
Brief description	yellowish needles
External identifiers / databases
EC number	205-749-9
ECHA InfoCard	100.005.228
PubChem	370
ChemSpider	361
Wikidata	Q375837
properties
Molar mass	170.12 g mol −1
Physical state	firmly
density	1.69 g cm −3
Melting point	253 ° C (decomposition)
pK s value	3.13 (COOH)
solubility	poor in cold water (11.9 g l −1 at 20 ° C), easy in warm water; soluble in ethanol , acetone and glycerine ; insoluble in benzene , chloroform and petroleum ether ;
safety instructions
GHS labeling of hazardous substances Caution
H and P phrases	H: 315-319-335
	P: 261-305 + 351 + 338
Toxicological data	5000 mg kg −1 ( LD 50 , rabbit , oral )
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

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

history

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

Several galls on a branch of an oak

Occurrence

Gallic acid is the building block of the vegetable tannin group of gallotannins and comes e.g. B. very rich in oak bark and gall apples . Compared to black tea , green tea contains ten times the amount of gallic acid and twice as much gallic acid as oolong tea .

synthesis

In the industrial production of gallic acid, molds are mostly used, whereby the enzyme tannase is formed. Tannase breaks down tannins into gallic acid and sugar . Gallic acid can also be obtained from aqueous extracts of gall apples or by hydrolytic cleavage with dilute acids.

properties

When gallic acid is heated, carbon dioxide is split off ( decarboxylation ) and pyrogallol (1,2,3-trihydroxybenzene) is formed.

use

Gallic acid is used to make iron gall inks (formerly), antioxidants in food, sunscreens and dyes (e.g. anthracene brown , gallamine blue , gallocyanine , rufigallic acid ).

Individual evidence

↑ Entry on GALLIC ACID in the CosIng database of the EU Commission, accessed on May 13, 2020.
↑ ^a ^b Entry for CAS no. 149-91-7 in the GESTIS substance database of the IFA , accessed on January 6, 2008(JavaScript required) .
↑ ^a ^b ^c ^d Entry on gallic acid. In: Römpp Online . Georg Thieme Verlag, accessed on December 25, 2014.
↑ ^a ^b ^c ^d Entry on gallic acid in the ChemIDplus database of the United States National Library of Medicine (NLM) .
↑ ^a ^b data sheet Gallic acid from Sigma-Aldrich , accessed on April 2, 2011 ( PDF ).

Web links

Commons : Gallic Acid - Collection of Images, Videos, and Audio Files

Wiktionary: Gallic acid - explanations of meanings, word origins, synonyms, translations

[CosIng-1] Entry on GALLIC ACID in the CosIng database of the EU Commission, accessed on May 13, 2020.

[GESTIS-2] Entry for CAS no. 149-91-7 in the GESTIS substance database of the IFA , accessed on January 6, 2008(JavaScript required) .

[roempp-3] Entry on gallic acid. In: Römpp Online . Georg Thieme Verlag, accessed on December 25, 2014.

[ChemIDplus-4] Entry on gallic acid in the ChemIDplus database of the United States National Library of Medicine (NLM) .

[Sigma-5] ta sheet Gallic acid from Sigma-Aldrich , accessed on April 2, 2011 ( PDF ).