Other authors gave other molecular formulas like C 28H 26O 15, while another formula found is C 28H 24O 11. In Allen's "Commercial Organic Analysis", published in 1912, the formula given was C 19H 16O 10. a tannic acid derived from ten molecules of gallic acid Īn electrostatic potential map (blue is positive and red is negative charge) of decagalloyl tannic acid, i.e. 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 (C 34H 30O 17). In 1880, Etti gave for it the molecular formula C 17H 16O 9. 202), the tannic acid of black tea is the same as that of oak-bark. It is precipitated by sulfuric acid in red flocks.
It differs however from the latter in not being convertible into gallic acid, and not yielding pyrogallic acid by dry distillation. It exhibits with ferric salts the same reactions as gallotannic acid. In 1865 in the fifth volume of "A dictionary of chemistry", Henry Watts wrote : In 1838, Jöns Jacob Berzelius wrote that quercitannate is used to dissolve morphine. It is described as a yellowish-brown amorphous powder. 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. The other form is called gallotannic acid and is found in oak galls. Quercitannic acid is one of the two forms of tannic acid found in oak bark and leaves. Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition. 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. The long-standing misuse of the terms, and its inclusion in scholarly articles has compounded the confusion. While tannic acid is a specific type of tannin (plant polyphenol), the two terms are sometimes (incorrectly) used interchangeably. It is a yellow to light brown amorphous powder. Sometimes extracts from chestnut or oak wood are also described as tannic acid but this is an incorrect use of the term. Commercial tannic acid is usually extracted from any of the following plant parts: Tara pods ( Caesalpinia spinosa), gallnuts from Rhus semialata or Quercus infectoria or Sicilian sumac leaves ( Rhus coriaria).Īccording to the definitions provided in external references such as international pharmacopoeia, Food Chemicals Codex and FAO-WHO tannic acid monograph only tannins obtained from the above-mentioned plants can be considered as tannic acid.
The chemical formula for commercial tannic acid is often given as C 76H 52O 46, 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. Its weak acidity ( pK a around 6) is due to the numerous phenol groups in the structure. Tannic acid is a specific form of tannin, a type of polyphenol. A bottle of tannic acid (water solution) from the redwood tree.