|Molar mass||170.12 g/mol|
|Appearance||White, yellowish-white, or
pale fawn-colored crystals.
|Density||1.694 g/cm3 (anhydrous)|
|Melting point||260 °C (500 °F; 533 K)|
|1.19 g/100 mL, 20°C (anhydrous)
1.5 g/100 mL, 20 °C (monohydrate)
|Solubility||soluble in alcohol, ether, glycerol, acetone
negligible in benzene, chloroform, petroleum ether
|Acidity (pKa)||COOH: 4.5, OH: 10.|
|Safety data sheet||External MSDS|
|Lethal dose or concentration (LD, LC):|
LD50 (Median dose)
|5000 mg/kg (rabbit, oral)|
|Benzoic acid, Phenol, Pyrogallol|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is: / ?)(|
Gallic acid is a trihydroxybenzoic acid, a type of phenolic acid, a type of organic acid, also known as 3,4,5-trihydroxybenzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H2(OH)3COOH. Gallic acid is found both free and as part of hydrolyzable tannins. The gallic acid groups are usually bonded to form dimers such as ellagic acid. Hydrolysable tannins break down on hydrolysis to give gallic acid and glucose or ellagic acid and glucose, known as gallotannins and ellagitannins respectively.
Gallic acid is commonly used in the pharmaceutical industry. It is used as a standard for determining the phenol content of various analytes by the Folin-Ciocalteau assay; results are reported in gallic acid equivalents. Gallic acid can also be used as a starting material in the synthesis of the psychedelic alkaloid mescaline.
Historical context and uses
Gallic acid is an important component of iron gall ink, the standard European writing and drawing ink from the 12th to 19th century with a history extending to the Roman empire and the Dead Sea Scrolls. Pliny the Elder (23-79 AD) describes his experiments with it and writes that it was used to produce dyes. Galls (also known as oak apples) from oak trees were crushed and mixed with water, producing tannic acid. It could then be mixed with green vitriol (ferrous sulfate) — obtained by allowing sulfate-saturated water from a spring or mine drainage to evaporate — and gum arabic from acacia trees; this combination of ingredients produced the ink.
Gallic acid was one of the substances used by Angelo Mai (1782–1854), among other early investigators of palimpsests, to clear the top layer of text off and reveal hidden manuscripts underneath. Mai was the first to employ it, but did so "with a heavy hand", often rendering manuscripts too damaged for subsequent study by other researchers.
Gallic acid was first studied by the Swedish chemist Carl Wilhelm Scheele in 1786. In 1818 the French chemist and pharmacist Henri Braconnot (1780–1855) devised a simpler method of purifying gallic acid from galls; gallic acid was also studied by the French chemist Théophile-Jules Pelouze (1807–1867), among others.
Gallic acid is formed from 3-dehydroshikimate by the action of the enzyme shikimate dehydrogenase to produce 3,5-didehydroshikimate. This latter compound tautomerizes to form the redox equivalent gallic acid, where the equilibrium lies essentially entirely toward gallic acid because of the coincidentally occurring aromatization.
- gallate + O2 → (1E)-4-oxobut-1-ene-1,2,4-tricarboxylate.
Gallate decarboxylase is another enzyme in the degradation of gallic acid.
Gallate 1-beta-glucosyltransferase is an enzyme that uses UDP-glucose and gallate, whereas its two products are UDP and 1-galloyl-beta-D-glucose.
Gallic acid is easily freed from gallotannins by acidic or alkaline hydrolysis. When gallic acid is heated with concentrated sulfuric acid, rufigallol is produced by condensation. Oxidation with arsenic acid, permanganate, persulfate, or iodine yields ellagic acid, as does reaction of methyl gallate with iron(III) chloride.
List of plants that contain gallic acid
- Gallic acid is found in oaks species like the North American white oak (Quercus alba) and European red oak (Quercus robur).
- Caesalpinia mimosoides
- stem bark of Boswellia dalzielii
- Drosera (sundew)
- Rhodiola rosea (golden root)
- Triphala (Ayurvedic herbal rasayana formula)
- Toona sinensis
- Urtica dioica (stinging nettle)
- Humulus lupulus (common hop)
- Areca nut
- Bearberry (Arctostaphylos sp)
- Bergenia sp
- Hot chocolate
- Juglans regia (Common walnut)
- Mango in peels and leaves
- Phyllanthus emblica (Indian gooseberry) in fruits
- Syzygium aromaticum (clove)
- Wine grape seeds
- Witch hazel (Hamamelis virginiana)
- White tea
|Lambda-max:||220, 271 nm (ethanol)
|Extinction coefficient (log ε)|
|Major absorption bands||ν : 3491, 3377, 1703, 1617, 1539, 1453, 1254 cm−1 (KBr)|
7.15 (2H, s, H-3 and H-7)
|Other NMR data|
|ESI-MS [M-H]- m/z : 169.0137 ms/ms (iontrap)@35 CE m/z product 125(100), 81(<1)|
Also known as galloylated esters:
- Methyl gallate
- Ethyl gallate, a food additive with E number E313
- Propyl gallate, or propyl 3,4,5-trihydroxybenzoate, an ester formed by the condensation of gallic acid and propanol
- Octyl gallate, the ester of octanol and gallic acid
- Dodecyl gallate, or lauryl gallate, the ester of dodecanol and gallic acid
- Epicatechin gallate, a flavan-3-ol, a type of flavonoid, present in green tea
- Epigallocatechin gallate (EGCG), also known as epigallocatechin 3-gallate, the ester of epigallocatechin and gallic acid, and a type of catechin
- Gallocatechin gallate (GCG), the ester of gallocatechin and gallic acid and a type of flavan-3ol
- Theaflavin-3-gallate, a theaflavin derivative
It is a weak carbonic anhydrase inhibitor. In basic research, gallic acid extracted from grape seeds has been shown to inhibit the formation of amyloid fibrils, one of the potential causes of Alzheimer's disease and Parkinson's disease. One study indicated that gallic acid has this effect on amyloid protein formation by modifying the properties of alpha-synuclein, a protein associated with the onset of neurodegenerative diseases.
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