What Is Tartaric Acid?
Tartaric acid, a hydroxycarboxylic acid with the formula C4H6O6, is known for its presence in many plants, especially grapes. It has a molecular weight of 150.1 and is also referred to as 2,3-dihydroxy succinic acid due to its specific structural arrangement. This acid is unique because it contains two chiral carbon atoms, leading to the existence of three isomers: L-tartaric acid, D-tartaric acid, and meso-tartaric acid, with L-tartaric acid being the most prevalent in nature.
Racemic tartaric acid, or grape acid, is a 1:1 mixture of the L- and D-forms. The melting points vary across these forms, with the L- and D-forms melting at 170°C, the meso-form at 151°C, and the racemic form at 206°C. Their CAS numbers are specific to each form, illustrating their distinct chemical identities.
Properties of Tartaric Acid
As a colorless solid, tartaric acid is soluble in polar solvents, with the racemic form being an exception in water solubility. Its production primarily involves the synthesis from potassium hydrogen tartrate, a byproduct of winemaking, through various chemical processes including the addition of calcium hydroxide or calcium carbonate, followed by extraction and acidification to yield tartaric acid.
Alternative synthetic methods involve the oxidation of maleic acid or fumaric acid, though these have not seen widespread practical application.
Uses of Tartaric Acid
Commonly used as a food additive, tartaric acid imparts a refreshing sour taste to soft drinks, jellies, jams, and sauces. Its salts, potassium hydrogen tartrate and sodium tartrate, serve as leavening agents that release carbon dioxide upon heating. In cosmetics, tartaric acid adjusts pH and acts as an astringent. It plays a role in organic synthesis as a naturally occurring asymmetric catalyst, notably in Sharpless oxidation for the specific synthesis of epoxides.
Other Information on Tartaric Acid
1. Origin of Tartaric Acid
The term “tartaric acid” was derived from its discovery in tartar, a sediment produced in winemaking. It is found in various natural sources, predominantly in grapes, and is characterized by a slight bitterness and sharp acidity.
2. Tartaric Acid and Its Mirror-Image Isomers
In 1849, Louis Pasteur’s isolation and study of tartaric acid salt crystals revealed the existence of mirror-image isomers. This discovery, illustrating that these isomers rotate polarized light in opposite directions, significantly contributed to the development of stereochemistry.