Tannic acid

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Tannic acid

Chemical structure of penta(digalloyl)glucose, a representative component of tannic acid
Names
IUPAC name
1,2,3,4,6-penta-O-{3,4-dihydroxy-5-[(3,4,5-trihydroxybenzoyl)oxy]benzoyl}-D-glucopyranose
Systematic 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
3D model (
JSmol
)
8186386
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.014.321 Edit this at Wikidata
IUPHAR/BPS
KEGG
UNII
  • InChI=1S/C76H52O46/c77-32-1-22(2-33(78)53(32)92)67(103)113-47-16-27(11-42(87)58(47)97)66(102)112-21-52-63(119-72(108)28-12-43(88)59(98)48(17-28)114-68(104)23-3-34(79)54(93)35(80)4-23)64(120-73(109)29-13-44(89)60(99)49(18-29)115-69(105)24-5-36(81)55(94)37(82)6-24)65(121-74(110)30-14-45(90)61(100)50(19-30)116-70(106)25-7-38(83)56(95)39(84)8-25)76(118-52)122-75(111)31-15-46(91)62(101)51(20-31)117-71(107)26-9-40(85)57(96)41(86)10-26/h1-20,52,63-65,76-101H,21H2/t52-,63-,64+,65-,76+/m1/s1 ☒N
    Key: LRBQNJMCXXYXIU-PPKXGCFTSA-N ☒N
  • InChI=1/C76H52O46/c77-32-1-22(2-33(78)53(32)92)67(103)113-47-16-27(11-42(87)58(47)97)66(102)112-21-52-63(119-72(108)28-12-43(88)59(98)48(17-28)114-68(104)23-3-34(79)54(93)35(80)4-23)64(120-73(109)29-13-44(89)60(99)49(18-29)115-69(105)24-5-36(81)55(94)37(82)6-24)65(121-74(110)30-14-45(90)61(100)50(19-30)116-70(106)25-7-38(83)56(95)39(84)8-25)76(118-52)122-75(111)31-15-46(91)62(101)51(20-31)117-71(107)26-9-40(85)57(96)41(86)10-26/h1-20,52,63-65,76-101H,21H2/t52-,63-,64+,65-,76+/m1/s1
    Key: LRBQNJMCXXYXIU-PPKXGCFTBB
  • Oc1cc(cc(O)c1O)C(=O)Oc1cc(cc(O)c1O)C(=O)OC[C@H]1O[C@H](OC(=O)c2cc(O)c(O)c(OC(=O)c3cc(O)c(O)c(O)c3)c2)[C@H](OC(=O)c2cc(O)c(O)c(OC(=O)c3cc(O)c(O)c(O)c3)c2)[C@@H](OC(=O)c2cc(O)c(O)c(OC(=O)c3cc(O)c(O)c(O)c3)c2)[C@@H]1OC(=O)c1cc(O)c(O)c(OC(=O)c2cc(O)c(O)c(O)c2)c1
Properties
C76H52O46
Molar mass 1701.19 g/mol
Density 2.12g/cm3
Melting point decomposes above 200 °C
2850 g/L or 250 g/L[1][2]
Solubility 100 g/L in ethanol
1 g/L in glycerol and acetone
insoluble in benzene, chloroform, diethyl ether, petroleum, carbon disulfide, carbon tetrachloride.
Acidity (pKa) ca. 6
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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redwood tree
.

Tannic acid is a specific form of

Rhus semialata or Quercus infectoria or Sicilian sumac leaves (Rhus coriaria
).

According to the definitions provided in external references such as international pharmacopoeia,

amorphous
powder.

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 many different types of tannins not just exclusively tannic acid.[3]

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

Quercitannic and gallotannic acids

gallotannic acid
and is found in oak galls.

The quercitannic acid molecule is also present in quercitron, a yellow dye obtained from the bark of the Eastern black oak (Quercus velutina), a forest tree indigenous in North America. It is described as a yellowish-brown amorphous powder.

In 1838, Jöns Jacob Berzelius wrote that quercitannate is used to dissolve morphine.[6]

In 1865 in the fifth volume of "A dictionary of chemistry", Henry Watts wrote :

It exhibits with ferric salts the same reactions as gallotannic acid. It differs however from the latter in not being convertible into

pyrogallic acid by dry distillation. It is precipitated by sulfuric acid in red flocks. (Stenhouse
, Ann. Ch. Pharm. xlv. 16.)
According to Rochleder (ibid lxiii. 202), the tannic acid of black tea is the same as that of oak-bark.[7]

In 1880, Etti gave for it the molecular formula C17H16O9. He described it as an unstable substance, having a tendency to give off water to form

anhydrides (called phlobaphenes), one of which is called oak-red (C34H30O17). For him, it was not a glycoside.[8][9]

An electrostatic potential map (blue is positive and red is negative charge) of decagalloyl tannic acid, i.e. a tannic acid derived from ten molecules of gallic acid

In Allen's "Commercial Organic Analysis", published in 1912, the formula given was C19H16O10.[10]

Other authors gave other molecular formulas like C28H26O15, while another formula found is C28H24O11.[11]

According to Lowe, two forms of the principle exist – "one soluble in water, of the formula C28H28O14, and the other scarcely soluble, C28H24O12. Both are changed by the loss of water into oak red, C28H22O11."[12]

Quercitannic acid was for a time a standard used to assess the phenolic content in spices, given as quercitannic acid equivalent.[13]

In an interesting historical note, the inventor of

Edward G. Acheson, discovered that gallotannic acid greatly improved the plasticity of clay. In his report of this discovery in 1904 he noted that the only known historical reference to the use of organic material added to clay is the use of straw mixed with clay described in the Bible, Exodus 1:11 and that the Egyptians must have been aware of his (re-)discovery. He stated "This explains why the straw was used and why the children of Israel were successful in substituting stubble for straw, a course that would hardly be possible, were the fibre of the straw depended upon as a bond feasible for the clay, but quite reasonable where the extract of the plant was used."[14]

Uses

Tannins are a basic ingredient in the chemical staining of

heartwood
.

Tannic acid is a common mordant used in the dyeing process for cellulose fibers such as cotton, often combined with alum and/or iron. The tannin mordant should be done first as metal mordants combine well with the fiber-tannin complex. However this use has lost considerable interest.

Similarly tannic acid can also be used as an aftertreatment to improve wash fastness properties of acid dyed polyamide. It is also an alternative for fluorocarbon aftertreatments to impart anti-staining properties to polyamide yarn or carpets. However, due to economic considerations currently the only widespread use as textile auxiliary is the use as an agent to improve chlorine fastness, i.e. resistance against dye bleaching due to cleaning with hypochlorite solutions in high-end polyamide 6,6-based carpets and swimwear. It is, however, used in relatively small quantities for the activation of upholstery flock; this serves as an anti-static treatment.

Tannic acid is used in the conservation of ferrous (iron based) metal objects to passivate and inhibit corrosion. Tannic acid reacts with the corrosion products to form a more stable compound, thus preventing further corrosion from taking place. After treatment the tannic acid residue is generally left on the object so that if moisture reaches the surface the tannic acid will be rehydrated and prevent or slow any corrosion. Tannic acid treatment for conservation is very effective and widely used but it does have a significant visual effect on the object, turning the corrosion products black and any exposed metal dark blue. It should also be used with care on objects with copper alloy components as the tannic acid can have a slight etching effect on these metals.

Tannic acid is also found in commercially available iron/steel corrosion treatments, such as Hammerite Kurust.

Use in food

In many parts of the world, its uses in food are permitted. In the United States, tannic acid is generally recognized as safe by the Food and Drug Administration for use in baked goods and baking mixes, alcoholic and non-alcoholic beverages, frozen dairy products, soft and hard candy, meat products, and rendered animal fat.[15]

According to

INS number assigned to tannic acid under the FAO-WHO Codex Alimentarius system.[16]

Uses as a medication

In conjunction with magnesium and sometimes activated charcoal, tannic acid was once used as a treatment for many toxic substances, such as strychnine, mushroom, and ptomaine poisonings in the late 19th and early 20th centuries.[17]

The introduction of tannic acid treatment of severe burn injuries in the 1920s significantly reduced mortality rates.[18] During World War I, tannic acid dressings were prescribed to treat "burns, whether caused by incendiary bombs, mustard gas, or lewisite".[19] After the war this use was abandoned due to the development of more modern treatment regimens.

Hazards

Tannic acid could cause potential health hazards such as damage to the eye, skin, respiratory tract, and gastrointestinal tract. It may cause irritation, redness, pain, blurred vision, and possible eye damage. When tannic acid is absorbed through the skin in harmful amounts, it may cause irritation, redness, and pain. Nausea, vomiting and diarrhoea are symptoms of tannic acid ingestion and prolonged exposure may cause liver damage. Upon inhalation, tannic acid may cause respiratory tract irritation.[20]

Crocodilian coloration

Skin color in Crocodilia (crocodiles and alligators) is very dependent on water quality. Algae-laden waters produce greener skin, while tannic acid in the water from decay of leaves from overhanging trees (which produces some types of blackwater rivers) often produce darker skin in these animals.[21]

References

  1. ^ "Tannic acid". American Chemical Society. 15 January 2018.
  2. ^ "Tannic acid". Chemical Book.
  3. PMID 432625
    .
  4. ISBN 978-2-7483-0811-2
    .
  5. ^ "Quercus Cortex. Oak Bark". Henriette's Herbal Homepage.
  6. ^ Traité de chimie, Volume 2. Jöns Jakob Berzelius (friherre) and Olof Gustaf Öngren, A. Wahlen et Cie., 1838[page needed]
  7. ^ Watts, Henry (1868). A Dictionary of chemistry and the allied branches of other sciences. Vol. 5. Longmans, Green, and Company. p. 6.
  8. S2CID 94578197
    .
  9. S2CID 105109992
    .
  10. doi:10.1016/S0140-6736(01)03766-7
    .
  11. OCLC 549678548.[page needed
    ]
  12. ^ Sayre, Lucius E. A manual of organic materia medica and pharmacognosy: An introduction to the study of the vegetable Kingdom and the vegetable and animal drugs (PDF) (Fourth ed.). p. 95.
  13. doi:10.1002/jps.3080121212
    .
  14. ^ Acheson, Edward G. (1904) "Egyptianized Clay" in Transactions of the American Ceramic Society. pp. 31–65.
  15. ^ "Food Additive Status List (GRAS); listing for tannic acid". US Food and Drug Administration. 24 October 2019. Retrieved 6 November 2020.
  16. ^
    doi:10.2903/j.efsa.2014.3828
    .
  17. ISSN 0096-9125
    .
  18. ^ "The use of tannic acid in the local treatment of burn wounds: intriguing old and new perspectives". Wounds. 13 (4): 144–58. 2001.
  19. ^ "Medicine: War Wounds". TIME. 18 September 1939. Archived from the original on May 30, 2008.
  20. ^ "Material Safety Data Sheet: Tannic Acid". fscimage.fishersci.com. Retrieved 10 September 2019.
  21. ^ "American Alligator: Species Profile". National Park Service. 17 October 2017. Retrieved 1 November 2018.

General references

The Merck Index, 9th edition, Merck & Co., Rahway, New Jersey, 1976.

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