Tannic acid
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Molecular Structure
Detailed Description
Tannic acid
EINECS: 215-753-2
Molecular Formula: C76H52O46
CAS Registry Number: 1401-55-4
Synonyms: Gallotannic acid,Gallotannin,Galloylglucose,Glycerite,Quebracho,Tannins
HS Code: 32019090
Appearance: light yellow to tan solid with a faint odor
Molecular Weight: 1701.22
Density: 2.12 g/cm3
Melting Point: 218℃
Flash Point: 198℃
Storage Temperature: Store in a cool, dry, well-ventilated area away from incompatible substances. Keep containers tightly closed. Store protected from light.
Refractive index: 1.927
Solubility: 250 g/L (20 °C) in water
Stability: Stable. Incompatible with metallic salts, strong oxidizing agents, iron and other heavy metals.
Usage: Mordant in dyeing, manufacture ink, sizing paper & silk, printing fabrics, tanning, as coagulant in rubber mfr, with gelatin & albumin for manufacture of imitation horn & tortoise shell, clarifying beer or wine, in photography, manufacture gallic acid & pyrogallol, as reagent in analytical chemistry.
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.
Tannins are a basic ingredient in the chemical staining of wood, and are already present in woods like oak, walnut, and mahogany. Tannic acid can be applied to woods low in tannin so chemical stains that require tannin content will react. The presence of tannins in the bark of redwood (Sequoia) is a strong natural defense against wildfire, decomposition and infestation by certain insects such as termites. It is found in the seeds, bark, cones, and 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.
- Tannic acid
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