Tartaric acid, chemical structure

Multiple Chiral Centers. The number of stereoisomers increases rapidly with an increase in the number of chiral centers in a molecule. A molecule possessing two chiral atoms should have four optical isomers, that is, four structures consisting of two pairs of enantiomers. However, if a compound has two chiral centers but both centers have the same four substituents attached, the total number of isomers is three rather than four. One isomer of such a compound is not chiral because it is identical with its mirror image it has an internal mirror plane. This is an example of a diaster-eomer. The achiral structure is denoted as a meso compound. Diastereomers have different physical and chemical properties from the optically active enantiomers. Recognition of a plane of symmetry is usually the easiest way to detect a meso compound. The stereoisomers of tartaric acid are examples of compounds with multiple chiral centers (see Fig. 1.14), and one of its isomers is a meso compound. 

To our knowledge, one alternative route to simple enantiopure quinuclidine-2-carboxylic acid has recently been described by Corey who assembled target molecule 68 whereas racemic 68 was first synthesized several decades ago by Prelog and [44]. Parent quinuclidine-2-carboxylic acid ester 68 that is structurally related to proline and pipecolinic acid was obtained from commercial 4-(2-hydroxyethyl)-piperidine in six chemical steps including one tartaric acid-mediated resolution (Scheme 12.17) [45]. A cyanoactivated intramolecular SN2 reaction delivered the strained [2.2.2]bicyclic system. The cyano group serves as a handle of further functionality and elaboration. 

The amine 2 is made by a chemical reaction - the reductive amination of ketone 1. The starting material 1 and the reagents are all achiral so the product 2, though chiral, must be racemic. Reaction with one enantiomer of tartaric acid 3 forms the amine salt 4, or rather the amine salts 4a and 4b. Examine these structures carefully. The stereochemistry of tartaric acid 3 is the same for both salts but the stereochemistry of the amine 2 is different so these salts 4a and 4b are diastereoisomers. They have different physical properties the useful distinction, discovered by trial and error, is that 4b crystallises preferentially from a solution in methanol leaving 4a behind in solution. Neutralisation of 4b with NaOH gives the free amine (S) -2, insoluble in water and essentially optically pure. 

In addition to tartaric acid another compound named paratartaric acid was found in wine sediments. Chemical analysis showed this compound to have the same composition as tartaric acid, so most scientists assumed the two compounds were identical. Strangely enough, however, paratartaric acid did not rotate plane-polarized fight. Pasteur would not accept the idea that such an experimental result could be an accident or unimportant. He guessed that even though the two compounds had the same chemical composition, they must somehow have different structures—and he set out to find evidence to prove his hypothesis. 

As (2, 3i )-(+)-tartaric acid can be genetically connected by chemical interactions with the D-series of organic compounds originating from D-glyceraldehyde, also (+)-tartaric acid can be considered a more refiable structure than D-glyceraldehyde. It turned out that the spatial formula adopted arbitrarily by Fischer proved to be the correct absolute configuration. On the other hand, Waser ascribed the opposite configuration for (+)-tartaric acid, but that was not confirmed. 

Cream of tartar is the potassium acid salt of tartaric acid. This means one acidic hydrogen of tartaric acid is replaced with a potassium ion. The structure is shown below. If you ve ever seen crystals of something in a bottle of wine (or even fresh grape juice), it was probably this chemical. 

FIGURE 8.14 Chemical structure of regular PEAs made from L-tartaric acid, succinic acid, and n-amino-l-alkanols. 

The chemical structure of tartaric acid is HOOC-HCOH-HOCH-COOH, which has two carbon atoms with four different substituents, that is, two centers of asymmetry. The natural tartaric acid is dextrorotatory. 

ViUuendas I., Molina I., Regano C., Bueno M., Martinez de Ilarduya A., Galbis J.A., Munoz-Guerra S., Hydrolytic degradation of poly(ester amidejs made from tartaric and succinic acids. Influence of the chemical structure and microstructure on degradation rate. Macromolecules, 32, 1999, 8033-8040. 

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