Paratartaric acid

Para-verblndung, /. para compound, -wein-saure, /. paratartaric acid (racemic acid), -xylol, n. paraxylene, p-xylene. parazentrisch, a. paracentric. 

Louis Pasteur encountered the phenomenon of optical activity in 1843, during his investigation of the crystalline sediment that accumulated in wine casks (a form of tartaric acid called paratartaric acid—also called racemic acid, from Latin racemus,... 

Pasteur devised three methods to resolve paratartaric acid the first was manual, the second was chemical, and the third could be considered biological or physiological. Because paratartaric acid (also called racemic acid) was the first inactive compound to be resolved into optical isomers (enantiomers, an equimolar mixture of two enantiomers is now called a racemate. 

Pasteur also discovered a method for resolving paratartaric acid while he was deeply involved in the study of fermentation. In essence, it depends on the capacity of certain microorganisms to discriminate between enantiomers and selectively to metabolize one instead of the other. This method is obviously less desirable than the chemical method since, at best, only one pure enantiomer can be obtained. The particular example described below by Pasteur in his second lecture grew out of his study of the fermentation of ammonium paratartrate. 

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. 

Acide rac mique, vinic acid, and TraubensSure all refer to an acid from grapes or wine. By the 1840s most French and English chemists were calling it paratartaric acid. 

Pararosaniline, N,N,N, N, N",N"-hexamethyl-, chloride. See Basic violet 3 Parasept. See Butylparaben Parasonar Mark . See Ethyl urocanate Paratartaric acid. See DL-Tartaric acid Paratherm NF. See Mineral oil Parathion CAS 56-38-2 UN NA 2783 (DOT)... 

CAS 133-37-9 EINECS/ELINCS 205-105-7 Synonyms Butanedioic acid, 2,3-dihydroxy-, (R,R)-( )- 2,3-Dihydroxybutanedioic acid (R,R)-( )-2,3-Dihydroxybutanedioic acid DL-Dihydroxysuccinic acid Paratartaric acid Racemic tartaric acid Resolvable tartaric acid ( )-Tartaric acid Uvic acid Empirical C4H6O6... 

The scientist whose name is most closely associated with early work on optical activity is Louis Pasteur (1822-1895). In 1844, while still a student in Paris, Pasteur read a recently published paper by Mitscherlich on the salts of the isomeric tartaric and paratartaric acids. The only known difference in the properties of the two acids and their salts was that the tartrates were optically active while the paratartrates were not. Mitscherlich reported that crystals of the sodium ammonium salts of tartaric and paratartaric acids were isomorphous and he therefore concluded that the nature and the number of atoms, their arrangement and their distances, are the same in the two substances compared . 

Pasteur was convinced that there must be some molecular difference between the two salts, and he made the problem the subject of his first major piece of research. He prepared several salts of tartaric acid and found that in all cases the crystals were asymmetric (Pasteur used the term dissymmetric), and displayed hemihedral faces. Pasteur was tempted to speculate that such asymmetric crystals were typical of optically active materials, and were the manifestation of asymmetry of the molecules. He then found that crystals of the optically inactive sodium ammonium paratartrate also displayed hemihedral faces, but on careful examination he saw that two types of crystal were present, one the mirror image of the other (Figure 10.13). He carefully sorted some of the crystals by hand. Those with right-handed hemihedry gave a solution which was dextrorotatory and identical with a solution of sodium ammonium tartrate. A solution of equal concentration of the crystals with left-handed hemihedry rotated polarised light to an equal extent in the opposite direction. A solution of equal concentrations of each crystalline form was optically inactive. Pasteur thereby demonstrated that paratartaric acid was... 

Further work by Pasteur showed that it was also possible to separate or resolve the two isomers present in paratartaric acid by forming a salt with a naturally occurring optically active base such as /-cinchonidine. The two salts had markedly different solubilities and could be separated by fractional crystallisation. A third method, also discovered by Pasteur, was to use a microorganism which consumed one of the enantiomers but not the other. Thus he found that the mould Penicillium... 

Pasteur converted rf-tartaric acid into paratartaric acid (and hence to the /-form) by heating the /-cinchonidine salt to 170 C and extracting the resulting mass with water. He also found that a fourth form of the acid, mesotartaric acid, was formed in this process. This was optically inactive but could not be resolved into enantiomers. 

Pasteur contended that the ability to produce an asymmetric molecule was a property of living organisms, and that an optically active material could never be obtained from an inactive precursor in the laboratory. He thought that all compounds displaying optical activity would have an inactive meso isomer, and that laboratory syntheses would result in such forms. He was forced to abandon this view in 1860 when W. H. Perkin (1838-1907) and B. F. Duppa made paratartaric acid from succinic acid. 

After van t Hoff published his theories on the tetrahedral carbon atom and on optical and geometric isomerism in 1874, much work was done to confirm his ideas by Johannes Adolf Wislicenus (1835-1902). He showed how the chemistry of maleic and fumaric acids was best explained if they were geometric isomers. The isomerism of Pasteur s tartaric acid was explained by proposing that it possessed two asymmetric carbon atoms, and that the meso form was inactive by internal compensation. Paratartaric acid was also known as racemic acid since it sometimes crystallises out from wine (the Latin racemus means a bunch of grapes). Inactive mixtures of optical antipodes are now known as racemic mixtures. 

So far, we have considered only nonchiral molecules, which have a plane of mirror symmetry, so the molecule is equal to its mirror image. However, there are molecules that are not symmetric when reflected, and they are called chiral. The first studies of the molecular chirality are dated back to the Ph.D. work of Louis Pasteur in 1848, when he observed the chiral separation of the crystals of tartaric and paratartaric acids in the sediments of fermenting wines. However, the definition of chiral objects was given first by Lord Kelvin only in 1893 "An object is chiral, if it cannot be superimposed on its mirror image."... 

A final and decisive progress was contributed by Pasteur [9-11] (1822-1895) and van t Hoff (1852-1908) [12]. Pasteur was troubled as a student by a report that salts of tartaric acid and paratartaric acid (i.e., the racemate) differed from each other by the optical rotation of tartrate solutions and absence of optical rotation in the case of paratartrates , although these salts had identical properties in aU other aspects. Careful examination of numerous salts of racemic tartaric acid led to an extremely important discovery. In the case of sodium-potassium or sodium ammonium salts he found equal amounts of heimhedral crystals which contained either the laevorotatory or the dextrorotatory molecules. In other words, he was able to separate the optical enantiomers in their crystalline form. About 20 years later Paterno published a rarely cited paper [13] in which he presented a tetrahedral... 

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