Tartaric acid
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Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes but also in tamarinds, bananas, avocados, and citrus.<ref name="pubchem"/> Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally in the process of fermentation. Potassium bitartrate is commonly mixed with sodium bicarbonate and is sold as baking powder used as a leavening agent in food preparation. The acid itself is added to foods as an antioxidant E334 and to impart its distinctive sour taste. Naturally occurring tartaric acid is a useful raw material in organic synthesis. Tartaric acid, an alpha-hydroxy-carboxylic acid, is diprotic and aldaric in acid characteristics and is a dihydroxyl derivative of succinic acid.
History
[edit]Tartaric acid has been known to winemakers for centuries. However, the chemical process for extraction was developed in 1769 by the Swedish chemist Carl Wilhelm Scheele.<ref>Retzius, Anders Jahan (1770) "Försök med vinsten och dess syra" (Experiments with cream of tartar and its acid), Kungliga Vetenskapsakademiens Handlingar (Proceedings of the Royal Academy of Sciences), 31 : 207–213. From p. 209: "§. 6. Dessa försök omtalte jag för Hr. Carl Wilhelm Scheele (en snabb och lårgirug Pharmaciæ Studiosus) … " (§. 6. I mention these experiments on behalf of Mr. Carl Wilhelm Scheele (a quick and studious student of pharmacology) … )</ref>
Tartaric acid played an important role in the discovery of chemical chirality. This property of tartaric acid was first observed in 1832 by Jean Baptiste Biot, who observed its ability to rotate polarized light.<ref>Biot (1835) "Mémoire sur la polarization circulaire et sur ses applications à la chimie organique" (Memoir on circular polarization and on its applications to organic chemistry), Mémoires de l'Académie des sciences de l'Institut, 2nd series, 13 : 39–175. That tartaric acid (acide tartarique cristallisé) rotates plane-polarized light is shown in Table G following p. 168. (Note: This article was read to the French Royal Academy of Sciences on 1832 November 5.)</ref><ref>Biot (1838) "Pour discerner les mélanges et les combinaisons chimiques définies ou non définies, qui agissent sur la lumière polarisée; suivies d'applications aux combinaisons de l'acide tartarique avec l'eau, l'alcool et l'esprit de bois" (In order to discern mixtures and chemical combinations, defined or undefined, which act on polarized light; followed by applications to combinations of tartaric acid with water, alcohol [i.e., ethanol], and spirit of wood [i.e., methanol]), Mémoires de l'Académie des sciences de l'Institut, 2nd series, 15 : 93–279.</ref> Louis Pasteur continued this research in 1847 by investigating the shapes of sodium ammonium tartrate crystals, which he found to be chiral. By manually sorting the differently shaped crystals, Pasteur was the first to produce a pure sample of levotartaric acid.<ref>Template:Cite journal</ref><ref>L. Pasteur (1848) "Sur les relations qui peuvent exister entre la forme cristalline, la composition chimique et le sens de la polarisation rotatoire" (On the relations that can exist between crystalline form, and chemical composition, and the sense of rotary polarization), Annales de Chimie et de Physique, 3rd series, 24 : 442–459.</ref><ref>Pasteur, Louis (1850) "Recherches sur les propriétés spécifiques des deux acides qui composent l'acide racémique" [Investigations into the specific properties of the two acids that compose racemic acid], Annales de Chimie et de Physique, 3rd series, 28 (3) : 56–99. See also Plate II. (See also the report of the commission that was appointed to verify Pasteur's findings, pp. 99–117.) [in French]</ref><ref>Template:Cite journal</ref><ref name=Flack>Template:Cite journal</ref>
Stereochemistry
[edit]Naturally occurring form of the acid is dextro tartaric acid or L-(+)-tartaric acid (obsolete name d-tartaric acid). Because it is available naturally, it is cheaper than its enantiomer and the meso isomer. The dextro and levo prefixes are archaic terms.<ref>Template:Cite web</ref> Modern textbooks refer to the natural form as (2R,3R)-tartaric acid (L-(+)-tartaric acid), and its enantiomer as (2S,3S)-tartaric acid (D-(−)-tartaric acid). The meso diastereomer is referred to as (2R,3S)-tartaric acid or (2S,3R)-tartaric acid.
- Dextro and levo form monoclinic sphenoidal crystals<ref>Template:Cite journal, based on P. Groth’s “Chemische Krystallographie".</ref> and orthorhombic crystals.
- Racemic tartaric acid forms monoclinic<ref name=CRC49>CRC Handbook of Chemistry and Physics, 49th edition.</ref> and triclinic crystals (space group PTemplate:Overline).<ref>Template:Cite web</ref><ref>Template:Cite journal, Template:Cite web</ref>
- Anhydrous meso tartaric acid form two anhydrous polymorphs: triclinic and orthorhombic.
- Monohydrated meso tartaric acid crystallizes as monoclinic and triclinic polymorphys depending on the temperature at which crystallization from aqueous solution occurs.<ref>Template:Cite journal</ref>
Tartaric acid in Fehling's solution binds to copper(II) ions, preventing the formation of insoluble hydroxide salts.
| DL-tartaric acid (racemic acid) (when in 1:1 ratio) | mesotartaric acid | |
|---|---|---|
| dextrotartaric acid (L-(+)-tartaric acid) |
levotartaric acid (D-(−)-tartaric acid) | |
| File:L-tartaric acid.png | File:D-tartaric acid.png | File:Meso-Weinsäure Spiegel.svg |
| Common name | Tartaric acid | Levotartaric acid | Dextrotartaric acid | Mesotartaric acid | Racemic acid |
|---|---|---|---|---|---|
| Synonyms | (2S,3S)-tartaric acid (S,S)-tartaric acid (−)-tartaric acid l-tartaric acid (obsolete) levotartaric acid Template:Sc-tartaric acid Template:Sc-threaric acid ("unnatural isomer")<ref>Template:Cite web</ref> |
(2R,3R)-tartaric acid (R,R)-tartaric acid (+)-tartaric acid d-tartaric acid (obsolete) Template:Sc-tartaric acid Template:Sc-threaric acid ("natural isomer")<ref>Template:Cite web</ref> |
(2R,3S)-tartaric acid meso-tartaric acid erythraric acid |
rac-(2R,3S)-tartaric acid (2RS,3SR)-tartaric acid (±)-tartaric acid Template:Sc-tartaric acid dl-tartaric acid (obsolete) paratartaric acid uvic acid | |
| PubChem | Template:PubChemCID | Template:PubChemCID | Template:PubChemCID | Template:PubChemCID | Template:PubChemCID |
| EINECS number | Template:EINECS | Template:EINECS | Template:EINECS | Template:EINECS | |
| CAS number | 526-83-0 | 147-71-7 | 87-69-4 | 147-73-9 | 133-37-9 |
Production
[edit]L-(+)-Tartaric acid
[edit]The L-(+)-tartaric acid isomer of tartaric acid is industrially produced in the largest amounts. It is obtained from lees, a solid byproduct of fermentations. The former byproducts mostly consist of potassium bitartrate (Template:Chem2). This potassium salt is converted to calcium tartrate (Template:Chem2) upon treatment with calcium hydroxide (Template:Chem2):<ref name=Ullman>J.-M. Kassaian "Tartaric acid" in Ullmann's Encyclopedia of Industrial Chemistry; VCH: Weinheim, Germany, 2002, 35, 671-678. Template:Doi</ref>
In practice, higher yields of calcium tartrate are obtained with the addition of calcium sulfate. Calcium tartrate is then converted to tartaric acid by treating the salt with aqueous sulfuric acid:
Racemic tartaric acid
[edit]Racemic tartaric acid can be prepared in a multistep reaction from maleic acid. In the first step, the maleic acid is epoxidized by hydrogen peroxide using Template:Ill as a catalyst.<ref name=Ullman/>
In the next step, the epoxide is hydrolyzed.
meso-Tartaric acid
[edit]A mixture of racemic acid and meso-tartaric acid is formed when dextro-Tartaric acid is heated in water at 165 °C for about 2 days. meso-Tartaric acid can also be prepared from dibromosuccinic acid using silver hydroxide:<ref name=Aug>Augustus Price West. Experimental Organic Chemistry. World Book Company: New York, 1920, 232-237.</ref>
meso-Tartaric acid can be separated from residual racemic acid by crystallization, the racemate being less soluble.
Reactivity
[edit]L-(+)-tartaric acid, can participate in several reactions. As shown the reaction scheme below, dihydroxymaleic acid is produced upon treatment of L-(+)-tartaric acid with hydrogen peroxide in the presence of a ferrous salt.
- HO2CCH(OH)CH(OH)CO2H + H2O2 → HO2CC(OH)C(OH)CO2H + 2 H2O
Dihydroxymaleic acid can then be oxidized to tartronic acid with nitric acid.<ref name=Blair>Template:Cite encyclopedia</ref>
Derivatives
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Important derivatives of tartaric acid include:
- Sodium ammonium tartrate, the first material separated into its enantiomers
- cream of tartar (potassium bitartrate), used in cooking
- Rochelle salt (potassium sodium tartrate), which has unusual piezoelectric properties
- tartar emetic (antimony potassium tartrate), a resolving agent.<ref>Template:Cite journal</ref><ref name="McCallum">Template:Cite journal</ref><ref>Template:Cite journal</ref> Diisopropyl tartrate is used as a co-catalyst in asymmetric synthesis.
Tartaric acid is a muscle toxin, which works by inhibiting the production of malic acid, and in high doses causes paralysis and death.<ref>Template:Cite book</ref> The median lethal dose (LD50) is about 7.5 grams/kg for a human, 5.3 grams/kg for rabbits, and 4.4 grams/kg for mice.<ref>Template:Cite book</ref> Given this figure, it would take over Template:Convert to kill a person weighing Template:Convert with 50% probability, so it may be safely included in many foods, especially sour-tasting sweets. As a food additive, tartaric acid is used as an antioxidant with E number E334; tartrates are other additives serving as antioxidants or emulsifiers.
When cream of tartar is added to water, a suspension results which serves to clean copper coins very well, as the tartrate solution can dissolve the layer of copper(II) oxide present on the surface of the coin. The resulting copper(II)-tartrate complex is easily soluble in water.
Tartaric acid in wine
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Tartaric acid may be most immediately recognizable to wine drinkers as the source of "wine diamonds", the small potassium bitartrate crystals that sometimes form spontaneously on the cork or bottom of the bottle. These "tartrates" are harmless, despite sometimes being mistaken for broken glass, and are prevented in many wines through cold stabilization (which is not always preferred since it can change the wine's profile). The tartrates remaining on the inside of aging barrels were at one time a major industrial source of potassium bitartrate.
Tartaric acid plays an important role chemically, lowering the pH of fermenting "must" to a level where many undesirable spoilage bacteria cannot live, and acting as a preservative after fermentation. In the mouth, tartaric acid provides some of the tartness in the wine, although citric and malic acids also play a role.
Tartaric acid in fruits
[edit]Grapes and tamarinds have the highest levels of tartaric acid concentration. Other fruits with tartaric acid are bananas, avocados, prickly pear fruit, apples, cherries, papayas, peaches, pears, pineapples, strawberries, mangoes and citrus fruits.<ref name="pubchem"/><ref>J.B. Gurtler, T.L. Mai, in Encyclopedia of Food Microbiology (Second Edition), 2014. PRESERVATIVES | Traditional Preservatives – Organic Acids: Tartaric Acid.</ref>
Trace amounts of tartaric acid have been found in cranberries and other berries.<ref>Phytochemicals of Cranberries and Cranberry Products: Characterization, Potential Health Effects, and Processing Stability https://www.researchgate.net/publication/44573816_Phytochemicals_of_Cranberries_and_Cranberry_Products_Characterization_Potential_Health_Effects_and_Processing_Stability</ref>
Tartaric acid is also present in the leaves and pods of Pelargonium plants and beans.
Applications
[edit]Tartaric acid and its derivatives have a plethora of uses in the field of pharmaceuticals. For example, it has been used in the production of effervescent salts, in combination with citric acid, to improve the taste of oral medications.<ref name="Blair" /> The potassium antimonyl derivative of the acid known as tartar emetic is included, in small doses, in cough syrup as an expectorant.
Tartaric acid also has several applications for industrial use. The acid has been observed to chelate metal ions such as calcium and magnesium. Therefore, the acid has served in the farming and metal industries as a chelating agent for complexing micronutrients in soil fertilizer and for cleaning metal surfaces consisting of aluminium, copper, iron, and alloys of these metals, respectively.<ref name=Ullman/>
Toxicity in canines
[edit]While tartaric acid is well-tolerated by humans and lab animals, an April 2021 letter to the editor of JAVMA hypothesized that the tartaric acid in grapes could be the cause of grape and raisin toxicity in dogs.<ref>Template:Cite web</ref><ref>Template:Cite journal</ref> Other studies have observed tartaric acid toxicity in kidney cells of dogs, but not in human kidney cells.<ref>Template:Cite journal</ref>
In dogs, the tartaric acid of tamarind causes acute kidney injury, which can often be fatal.<ref>Template:Cite journal</ref>
A review identified a relationship between grape ingestion and illness, though the specific type or quantity of grapes that cause toxicity remains unclear. Grape ingestion commonly leads to gastrointestinal and/or renal issues, with treatment depending on the symptoms; outcomes can vary.<ref>Template:Cite journal</ref>