Gallic acid
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Names | |||
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Preferred IUPAC name
3,4,5-Trihydroxybenzoic acid | |||
Other names
Gallic acid
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Identifiers | |||
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ECHA InfoCard
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100.005.228 | ||
EC Number |
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KEGG | |||
PubChem CID
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RTECS number
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Properties | |||
C7H6O5 | |||
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 | ||
log P | 0.70 | ||
Acidity (pKa) | COOH: 4.5, OH: 10. | ||
-90.0·10−6 cm3/mol | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards
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Irritant | ||
NFPA 704 (fire diamond) | |||
Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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5000 mg/kg (rabbit, oral) | ||
Safety data sheet (SDS) | External MSDS | ||
Related compounds | |||
Related
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phenols, carboxylic acids | ||
Related compounds
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Benzoic acid, Phenol, Pyrogallol | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a
Its name is derived from
Isolation and derivatives
Gallic acid is easily freed from gallotannins by acidic or alkaline hydrolysis. When heated with concentrated sulfuric acid, gallic acid converts to rufigallol. Hydrolyzable tannins break down on hydrolysis to give gallic acid and glucose or ellagic acid and glucose, known as gallotannins and ellagitannins, respectively.[2]
Biosynthesis
Gallic acid is formed from
Reactions
Oxidation and oxidative coupling
Alkaline solutions of gallic acid are readily oxidized by air. The oxidation is catalyzed by the enzyme gallate dioxygenase, an enzyme found in Pseudomonas putida.
Oxidative coupling of gallic acid with arsenic acid, permanganate, persulfate, or iodine yields
Hydrogenation
Hydrogenation of gallic acid gives the cyclohexane derivative hexahydrogallic acid.[6]
Decarboxylation
Heating gallic acid gives pyrogallol (1,2,3-trihydroxybenzene). This conversion is catalyzed by gallate decarboxylase.
Esterification
Many esters of gallic acid are known, both synthetic and natural. Gallate 1-beta-glucosyltransferase catalyzes the glycosylation (attachment of glucose) of gallic acid.
Historical context and uses
Gallic acid is an important component of
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.[9]
Gallic acid was first studied by the Swedish chemist Carl Wilhelm Scheele in 1786.[10] In 1818, French chemist and pharmacist Henri Braconnot (1780–1855) devised a simpler method of purifying gallic acid from galls;[11] gallic acid was also studied by the French chemist Théophile-Jules Pelouze (1807–1867),[12] among others.
When mixed with acetic acid, gallic acid had uses in early types of photography, like the calotype to make the silver more sensitive to light; it was also used in developing photographs.[13]
Occurrence
Gallic acid is found in a number of
Esters
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
Gallate esters are antioxidants useful in food preservation, with propyl gallate being the most commonly used. Their use in human health is scantly supported by evidence.
Spectral data
UV-Vis
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Lambda-max :
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220, 271 nm (ethanol) |
Extinction coefficient (log ε)
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IR | |
Major absorption bands | ν : 3491, 3377, 1703, 1617, 1539, 1453, 1254 cm−1 (KBr) |
NMR
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Proton NMR
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δ : 7.15 (2H, s, H-3 and H-7) |
Carbon-13 NMR
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δ : 167.39 (C-1), |
Other NMR data | |
MS
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Masses of main fragments |
ESI-MS [M-H]- m/z : 169.0137 ms/ms (iontrap)@35 CE m/z product 125(100), 81(<1) |
See also
- Benzoic acid
- Catechol
- Hydrolyzable tannin
- Pyrogallol
- Syringol
- Syringaldehyde
- Syringic acid
- Shikimic acid
References
- PMID 15206456.
- ^ Andrew Pengelly (2004), The Constituents of Medicinal Plants (2nd ed.), Allen & Unwin, pp. 29–30
- ^ Gallic acid pathway on metacyc.org
- PMID 5807212.
- ^ a b Edwin Ritzer; Rudolf Sundermann (2007), "Hydroxycarboxylic Acids, Aromatic", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, p. 6
- .
- ^ Pliny the Elder with John Bostock and H.T. Riley, trans., The Natural History of Pliny (London, England: Henry G. Bohn, 1857), vol. 6, p. 196. In Book 34, Chapter 26 of his Natural History, Pliny states that verdigris (a form of copper acetate (Cu(CH3COO)2·2Cu(OH)2), which was used to process leather, was sometimes adulterated with copperas (a form of iron(II) sulfate (FeSO4·7H2O)). He presented a simple test for determining the purity of verdigris. From p. 196: "The adulteration [of verdigris], however, which is most difficult to detect, is made with copperas; … The fraud may also be detected by using a leaf of papyrus, which has been steeped in an infusion of nut-galls; for it becomes black immediately upon the genuine verdigris being applied."
- ^ Fruen, Lois. "Iron Gall Ink". Archived from the original on 2011-10-02.
- ^ L.D. Reynolds and N.G. Wilson, "Scribes and Scholars" 3rd Ed. Oxford: 1991, pp 193–4.
- ^ Carl Wilhelm Scheele (1786) "Om Sal essentiale Gallarum eller Gallåple-salt" (On the essential salt of galls or gall-salt), Kongliga Vetenskaps Academiens nya Handlingar (Proceedings of the Royal [Swedish] Academy of Science), 7: 30–34.
- ^ Braconnot Henri (1818). "Observations sur la préparation et la purification de l'acide gallique, et sur l'existence d'un acide nouveau dans la noix de galle" [Observations on the preparation and purification of gallic acid, and on the existence of a new acid in galls]. Annales de Chimie et de Physique. 9: 181–184.
- ^ J. Pelouze (1833) "Mémoire sur le tannin et les acides gallique, pyrogallique, ellagique et métagallique," Annales de chimie et de physique, 54: 337–365 [presented February 17, 1834].
- ISBN 978-1-58839-225-1.
- PMID 23344249.
- .
- PMID 10999626.
- ^ .
- ^ Alemika, Taiwo E.; Onawunmi, Grace O.; Olugbade, Tiwalade A. (2007). "Antibacterial phenolics from Boswellia dalzielii". Nigerian Journal of Natural Products and Medicine. 10 (1): 108–10.
- ^ PMID 26251571.
- PMID 17420579.
- PMID 10888536.
- S2CID 95396304.
- S2CID 91784893.
- PMID 27834921.