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Tannic acid

Tannic acid
Tannic acid.svg
Names
IUPAC name
2,3-dihydroxy-5-({[(2R,3R,4S,5R,6R)-3,4,5,6-tetrakis({3,4-dihydroxy-5-[(3,4,5-trihydroxyphenyl)carbonyloxy]phenyl}carbonyloxy)oxan-2-yl]methoxy}carbonyl)phenyl 3,4,5-trihydroxybenzoate
Other names
Acidum tannicum
Gallotannic acid
Digallic acid
Gallotannin
Tannimum
Quercitannin
Oak bark tannin
Quercotannic acid
Querci-tannic acid
Querco-tannic acid
Identifiers
1401-55-4 YesY
3D model (Jmol) Interactive image
8186386
ChEBI CHEBI:75211 N
ChEMBL ChEMBL506247 N
ChemSpider 17286569 N
ECHA InfoCard 100.014.321
4319
KEGG C13452 N
PubChem 16129878
UNII 28F9E0DJY6 N
Properties
C76H52O46
Molar mass 1701.19 g/mol
Melting point decomposes above 200 °C
2850 g/L
Acidity (pKa) ca. 10
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Tannic acid is a specific commercial form of tannin, a type of polyphenol. Its weak acidity (pKa around 10) is due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as C76H52O46, which corresponds with decagalloyl glucose, but in fact it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12 depending on the plant source used to extract the tannic acid. Commercial tannic acid is usually extracted from any of the following plant part: Tara pods (Caesalpinia spinosa), gallnuts from Rhus semialata or Quercus infectoria or Sicilian Sumac leaves (Rhus coriaria).

According to the definitions provided in external references such as international pharmacopoeia, Food Chemicals Codex and FAO-WHO tannic acid monograph only tannins sourced from the above-mentioned plants can be considered as tannic acid. Sometimes extracts from chestnut or oak wood are also described as tannic acid but this is an incorrect use of the term. It is a yellow to light brown amorphous powder; 2850 grams dissolves in one litre of water (1.7 moles per liter).

While tannic acid is a specific type of tannin (plant polyphenol), the two terms are sometimes (incorrectly) used interchangeably. The long-standing misuse of the terms, and its inclusion in scholarly articles has compounded the confusion. This is particularly widespread in relation to green tea and black tea, both of which contain tannin but not tannic acid.

Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition.


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