Tartaric acid is a white crystalline diprotic aldaric acid. It is predominantly found naturally in several plants, in particular bananas, grapes, and tamarinds. It is a useful raw material in organic chemistry for the synthesis of other chiral molecules.
L-(+)-tartaric acid is obtained from a naturally-occurring component of lees, a solid by-product of fermentation. The former by-products mostly consist of potassium bitartrate (KHC4H4O6).
This potassium salt is converted to calcium tartrate (CaC4H4O6) upon treatment with milk of lime (Ca(OH)2):
KO2CCH(OH)CH(OH)CO2H + Ca(OH)2 → Ca(O2CCH(OH)CH(OH)CO2) + KOH + H2O
Higher yields of calcium tartrate are obtained with the addition of calcium chloride. Calcium tartrate is then converted to tartaric acid by treating the salt with aqueous sulfuric acid.
This process yields L-(+)-tartaric acid:
Ca(O2CCH(OH)CH(OH)CO2) + H2SO4 → HO2CCH(OH)CH(OH)CO2H + CaSO4
L(+)-Tartaric acid is widely used as an acidulant in beverages and other food products such as soft drinks, wine, candy, bread and some colloidal sweetmeats. Tartaric acid is also commonly combined with baking soda to function as a leavening agent in recipes and is one of the main acids found in wine. It is added to give a sour taste and is used as an antioxidant under E number E334.
Tartaric acid is used with citric acid in effervescent salts production which improves the taste of oral medications. The potassium antimonyl derivative of the acid known as tartar emetic is included, in small doses, in cough syrup as an expectorant.
Tartaric acid has several applications for agricultural use such as a chelating agent. Its chelating properties on metal ions drives its popularity in the farming industry for purposes such as complexing micronutrients in soil fertilizer.
It is also used in the metal industries as a chelating agent for cleaning metal surfaces consisting of aluminum, copper, iron, and alloys of these metals. With its reduction properties, it is also used as a reductive agent in manufacturing mirror chemically or imaging agent in photography. Its acidity can also be used as a catalyst in the resin finishing of polyester fabric or pH value regulator in oryzanol production.