Gallic acid

Gallic acid
IUPAC name 3,4,5-trihydroxybenzoic acid
Other names Gallic acid Gallate 3,4,5-trihydroxybenzoate
Identifiers
CAS number	149-91-7 Y, [5995-86-8] (Monohydrate)
PubChem	370
ChemSpider	361 Y
UNII	632XD903SP Y
KEGG	C01424 Y
ChEBI	CHEBI:30778 Y
ChEMBL	CHEMBL288114 Y
Jmol-3D images	Image 1
SMILES O=C(O)c1cc(O)c(O)c(O)c1
InChI InChI=1S/C7H6O5/c8-4-1-3(7(11)12)2-5(9)6(4)10/h1-2,8-10H,(H,11,12) Y Key: LNTHITQWFMADLM-UHFFFAOYSA-N Y InChI=1/C7H6O5/c8-4-1-3(7(11)12)2-5(9)6(4)10/h1-2,8-10H,(H,11,12) Key: LNTHITQWFMADLM-UHFFFAOYAN
Properties
Molecular formula	C7H6O5
Molar mass	170.12 g/mol
Exact mass	170.021523 u
Appearance	White, yellowish-white, or pale fawn-colored crystals.
Density	1.7 g/cm3 (anhydrous)
Melting point	250 °C, 523 K, 482 °F
Solubility in water	1.1 g/100 ml water @ 20°C (anhydrous) 1.5 g/100 ml water @ 20 °C (monohydrate)
Acidity (pKa)	COOH: 4.5, OH: 10.
Hazards
MSDS	External MSDS
Main hazards	Irritant
Related compounds
Related compounds	Benzoic acid, Phenol, Pyrogallol
Y acid (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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.^[1] The chemical formula is C₆H₂(OH)₃COOH. Gallic acid is found both free and as part of tannins. Salts and esters of gallic acid are termed 'gallates'. Despite its name, it does not contain gallium.

Gallic acid is commonly used in the pharmaceutical industry.^[2] 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.^[3] Gallic acid can also be used as a starting material in the synthesis of the psychedelic alkaloid mescaline.^[4]

Gallic acid seems to have anti-fungal and anti-viral properties. Gallic acid acts as an antioxidant and helps to protect human cells against oxidative damage. Gallic acid was found to show cytotoxicity against cancer cells, without harming healthy cells. Gallic acid is used as a remote astringent in cases of internal haemorrhage. Gallic acid is also used to treat albuminuria and diabetes. Some ointments to treat psoriasis and external haemorrhoids contain gallic acid.^[5]

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 gallic acid (hence the name). It could then be mixed with green vitriol (ferrous sulfate), obtained by allowing sulfate saturated spring or mine drainage water to evaporate, and gum arabic from acacia trees to produce the ink^[6] .

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 damaging manuscripts for future study.^{[citation needed]}

It has been discovered by French chemist and pharmacist Henri Braconnot (1780–1855) in 1818 and studied by French chemist Théophile-Jules Pelouze (1807–1867).

Early photographers also used it, Joseph Bancroft Reade (1801–1870) for instance and William Fox Talbot (1800–1877) for developing latent images in calotypes. It has also been used as a coating agent in zincography.

It was also used by George Washington to communicate with spies during the United States war for independence (American Revolution) according to the miniseries "America the Story of Us."

Gallic acid is a component of some whistle mixtures.

List of plants or foods that contain the chemical

• Areca nut
• Bearberry (Arctostaphylos sp)
• Bergenia sp
• Blackberry
• Caesalpinia mimosoides^[7]
• Hot chocolate
• Drosera (sundew)
• Juglans regia (Common walnut)
• Mango in peels and leaves
• Phyllanthus emblica (Indian gooseberry) in fruits
• Raspberry
• Syzygium aromaticum (clove)^[8]
• Rhodiola rosea (Golden root)
• Triphala (Ayurvedic herbal rasayana formula)
• Witch hazel (Hamamelis virginiana)
• White tea
• Toona sinensis

Spectral data

UV-Vis
Retention time
Lambda-max:	220, 271 nm (ethanol) Spectrum of gallic acid
Extinction coefficient (log ε)
IR
Major absorption bands	ν : 3491, 3377, 1703, 1617, 1539, 1453, 1254 cm−1 (KBr)
NMR
Proton NMR (acetone-d6): d : doublet, dd : doublet of doublets, m : multiplet, s : singlet	δ : 7.15 (2H, s, H-3 and H-7)
Carbon-13 NMR (acetone-d6):	δ : 167.39 (C-1), 144.94 (C-4 and C-6), 137.77 (C-5), 120.81 (C-2), 109.14 (C-3 and C-7)
Other NMR data
MS
Masses of main fragments	ESI-MS [M-H]- m/z : 169.0137

Reference^[7]

Esters

Also known as galloylated esters:

• 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

Metabolism

Gallate 1-beta-glucosyltransferase (EC 2.4.1.136) is an enzyme that uses UDP-glucose and gallate, whereas its two products are UDP and 1-galloyl-beta-D-glucose.

Gallate decarboxylase (EC 4.1.1.59)is another enzyme.

See also

• Pyrogallol
• Syringol
• Syringaldehyde
• Tannin
• Shikimic acid

References

1. ^ LD Reynolds and NG Wilson, “Scribes and Scholars” 3rd Ed. Oxford: 1991. pp193–4.
2. ^ S. M. Fiuza. "Phenolic acid derivatives with potential anticancer properties––a structure–activity relationship study. Part 1: Methyl, propyl and octyl esters of caffeic and gallic acids". Elsevier. doi:10.1016/j.bmc.2004.04.026. 
3. ^ Andrew Waterhouse. "Folin-Ciocalteau Micro Method for Total Phenol in Wine". UC Davis. http://waterhouse.ucdavis.edu/phenol/folinmicro.htm. 
4. ^ Tsao, Makepeasce (July 1951). "A New Synthesis Of Mescaline". Journal of the American Chemical Society 73 (11): 5495–5496. doi:10.1021/ja01155a562. ISSN 0002-7863. 
5. ^ phytochemicals.info
6. ^ Fruen, Lois. "Iron Gall Ink". http://www.realscience.breckschool.org/upper/fruen/files/Enrichmentarticles/files/IronGallInk/IronGallInk.html. 
7. ^ ^{a b} Antimicrobial gallic acid from Caesalpinia mimosoides Lamk. Anchana Chanwitheesuk, Aphiwat Teerawutgulrag, Jeremy D. Kilburn and Nuansri Rakariyatham, Food Chemistry, Volume 100, Issue 3, 2007, pp. 1044-1048, doi:10.1016/j.foodchem.2005.11.008
8. ^ Pathak, S. B. et al.; Niranjan, K.; Padh, H.; Rajani, M. (2004). "TLC Densitometric Method for the Quantification of Eugenol and Gallic Acid in Clove". Chromatographia 60 (3 - 4): 241–244. doi:10.1365/s10337-004-0373-y. 

External links

• King's American Dispensatory (1898) entry on Gallic acid