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Tartaric acid, or 2,3-dihydroxysuccinic acid, it is a carboxylic acid with the chemical formula C4H6O6. Exist in a variety of plants, such as grapes and tamarind. It is also one of the main organic acids in wine.
As an antioxidant added to food, it can make food have a sour taste. The biggest use of tartaric acid is a beverage additive and a raw material for the pharmaceutical industry.
There are three main methods for preparing tartaric acid:
1. The preparation of DL-tartaric acid is obtained by oxidizing fumaric acid or maleic acid.
2. It is obtained by reacting glyoxal with hydrocyanic acid and then acid hydrolysis. D-tartaric acid, found in many fruits or other parts of plants, exists in a free state, and also exists in a combined state with potassium, calcium and magnesium.
3. Tartaric acid is prepared from the crude tartar precipitate generated during wine production, extracted from potassium hydrogen tartrate, converted into calcium tartrate, acidified with dilute sulfuric acid, or obtained by oxidizing D-glucose with nitric acid. The preparation of DL-tartaric acid is to azeotrope D-tartaric acid with NaOH aqueous solution. 49 grams of maleic anhydride, 0.25 grams of tungstic acid, 130 grams of 30% hydrogen peroxide and 50 milliliters of water were mixed uniformly, and the reaction was stirred at 70° C. for 8 hours, and then flowed for 1 hour. The reaction solution was cooled, 5 ml of concentrated sulfuric acid was added, and the mixture was heated and boiled for 1 hour. On cooling, crystals precipitated. Filter, wash the filter cake with water 3 times, drain and dry to obtain 5 g of tartaric acid.
Tartrates have historically played a role in establishing organic stereochemistry. In 1769, Scheler first obtained free colorless tartaric acid crystals from the fermentation broth of grape juice. Its various stereoisomers and racemates have different physical properties. Most of them are dextrorotatory bodies in nature, especially in grape juice and other berry juices, so they are also called fruit acids. The racemate is obtained as controlled oxidation with butenedioic acid. The tartar produced in the above-mentioned reaction process is treated with lime milk to generate calcium tartrate, and then acidified to obtain meso. In 1848, when French chemist Pasteur was working on the crystallography of sodium ammonium tartrate, he saw an interesting phenomenon that no one had noticed before: the non-optically active sodium ammonium tartrate is a mixture of two different crystals, and their shapes are mirror images of each other, and they are actually racemates. Using a magnifying glass and tweezers, he carefully divided the mixture into small piles. A pile of dextrorotatory crystals and a pile of left-handed crystals are like a pile of right glove and a pile of left glove. Both crystals are optically active when dissolved in water. He discovered the relationship between the stereoisomerism and optical rotation of molecules for the first time, put forward the concept of enantiomer, and laid the foundation for the development of organic stereochemistry.
Tartaric acid has two identical chiral carbon atoms, and there are three stereoisomers (left-handed (L-tartaric acid), dextrorotated (D-tartaric acid), meso-form). L-tartaric acid and dextro-tartaric acid are enantiomers. Naturally occurring tartaric acids are all dextromeric forms. D-tartaric acid is widely distributed in higher plants in the form of free potassium salt, calcium salt and magnesium salt, especially in fruits and leaves. When making wine, large amounts of tartar (hydropotassium) are deposited. In addition, it is also commonly found in molds and lichens. A mixture of equal amounts of levorotatory and dextrorotatory forms, whose optical activities cancel each other out, form a racemate. Racemic tartaric acid is also known as grape acid. During the fermentation process of grape juice or other berry juice, the acid potassium salt of dextro-tartaric acid insoluble in ethanol and water is deposited on the wall of the wine barrel, which is called tartar, and the name of tartaric acid is derived from this. L-tartaric acid can be obtained from the separation of the racemate, and also exists in the fruit and leaves of the Malian carp.
Melting point: 200-206℃
Boiling point: 399.3℃
Flash point: 210℃
Solubility: soluble in water and ethanol, slightly soluble in ether.
Tartaric acid is often used in the preparation of drugs, mordants and tanning agents, and it is also commonly used as a reagent for the resolution of racemic basic compounds. It is also a sour agent in food additives, and its acidity is better than that of malic acid and lactic acid. Several of its salts have important applications, such as the preparation of Fehling's reagent with potassium sodium tartrate in the laboratory, which is used to identify aldehyde functional groups in organic molecular structures. Its potassium and sodium salt is also called Rochelle salt, and its crystal is polarized under pressure to generate a potential difference (piezoelectric effect) on both ends of the surface, which can be used to make piezoelectric components for radio and cable broadcasting receivers and pickups. Antimony potassium tartrate (commonly known as spit tartar) is medically used to treat schistosomiasis.