Tartaric acid dextro

On studying the sodium-ammonium salt of ordinary tartaric acid (dextro tartaric acid), to see if there was any indication of unsymmetrical crystalline form with which to connect the optical activity, according to the suggestion of Herschel, Pasteur observed that the crystals possessed hemi-hedral facets. These gave to the crystals an unsymmetrical form. He then turned his attention to the second known tartaric acid, viz., racemic acid, which is optically inactive. His expectation was that in this acid no such unsymmetrical form would exist as it did not possess optical activity. But to his surprise he found, in the crystals of the sodium-ammonium salt, the same hemi-hedral facets that he had just found in the salts of the active acid. On closer examination. 

Tartaric acid (dextro-tartaric acid) has been employed for a long time as a substrate in carbohydrate synthesis, especially in the held of tetroses. In the past decade Nakagawa and co-workers improved the preparation of L-threose. Methyl hydrogen di-O-acetyl-c/gxtro-tartrate (384) was reduced with sodium borohydride in water solution to L-threono- y-lactone (385) in 74% yield. Further reduction of the lactone grouping with bis(3-methyl-2-butyl) borane to the aldehyde stage proceeded smoothly and afforded L-threose in about 63% yield. 

Tartaric acid [526-83-0] (2,3-dihydroxybutanedioic acid, 2,3-dihydroxysuccinic acid), C H O, is a dihydroxy dicarboxyhc acid with two chiral centers. It exists as the dextro- and levorotatory acid the meso form (which is inactive owing to internal compensation), and the racemic mixture (which is commonly known as racemic acid). The commercial product in the United States is the natural, dextrorotatory form, (R-R, R )-tartaric acid (L(+)-tartaric acid) [87-69-4]. This enantiomer occurs in grapes as its acid potassium salt (cream of tartar). In the fermentation of wine (qv), this salt forms deposits in the vats free crystallized tartaric acid was first obtained from such fermentation residues by Scheele in 1769. 

In general, the maximum number of optically active isomers is given by 2n where n represents the number of asymmetric carbon atoms. Thus for a compound where n = 1, as in lactic acid, there would be two stereoisomers, one the dextro and the other the laevo. For a compound with two asymmetric carbon atoms, there would be 22 = 4 stereoisomers. But if the two asymmetric carbon atoms carry exactly identical groups, as in tartaric acid, the number would be fewer than four and we know that it exists in three forms, the d the 1 and the meso. 

Raemie aeid is a compound of dextro and lsevo>tartaric acids. It may be produced by tiniting them, and may again bo resolved into them. 

For a long time, this reaction was conducted exclusively with acety-lated nitriles of aldonic acids, and the products obtained were known in general as "aldose-amides. Fischer2 used this reaction to transform tetra-O-acetyl-L-rhamnononitrile into l,l-bis(acetamido)-l,5-dideoxy-L-arabinitol, whose subsequent hydrolysis and oxidation allowed him to determine the configuration of dextro-tartaric acid (L-threaric acid). 

Later, Pasteur 15) had arrived at the general stereochemical criterion for a chiral or dissymmetric molecular structure. Thus, the specific rotations of the two sets of sodium ammonium tartrate crystals in solution, isolated from the racemic mixture by hand-picking, were equal in magnitude and opposite in sign, from which Pasteur inferred that enantiomorphism of the dextro- and laevorotatory crystals is reproduced in the microscopic stereochemistry of the (+)- and (—)-tartaric acid molecules. The term dissymmetry or chirality is used when there is no superimposability between the two enantiomers, as seen in Sect. 2.1. 

Tartaric acid can be obtained in four forms dextro-, laevo-, meso- and the mixed-isomer equilibrium, or racemic, form. Commercially, it is usually available as cferfro-tartaric acid. This acid has a sharper flavour than citric and it may therefore be used at a slightly lower level to give equivalent palate acidity. (Palate acidity is a purely subjective evaluation and it is generally agreed that a number of acids can be used at concentrations different from those indicated by their chemical acid equivalent, see Table 5.3.)... 

Some interest also attaches, on stereochemical grounds, to the effects of the isomers of tartaric acid and malic acid. At 0.01 M, erythraric acid (meso-tartaric acid) caused slight competitive inhibition,181 183 186 whilst d- or L-threaric acid (levo- or dextro-tartaric acid) had no effect138181 commercial DL-threaric acid ( racemic acid ) had a small effect that disappeared on purification.181 Some authors have noted slight inhibition with L-tartaric acid.147 166 183 L-Malic acid resembled erythraric acid in its action,136 147 1 65 188,185 but n-malic acid appeared to be non-inhibitory.136-183 Unsubstituted w-dicarboxylic acids cause little, if any, inhibition.135 147 166183... 

Biochemical Resolution (Pasteur s Third Method).96 Pasteur observed that, when salts of eZZ-tartaric acid were introduced into cultures of yeast or of certain molds, the dextro component was decomposed com-... 

Chemists have known about racemates since Pasteur, at 26 years of age, told the Paris Academy of Sciences how he used tweezers to separate two types of crystals of salts of tartaric acid, which rotate polarized light clockwise (d, dextro) or counterclockwise (l, levo). Unfortunately, this correspondence does not always hold true. In fact, the magnitude and even the direction of optical rotation are complicated functions of the electronic structure surrounding the chiral center. For example, the common enantiomer of the sugar fructose is termed d because of the stereochemical orientation about the chiral atom. But this enantiomer actually rotates the plane of polarization to the left, and its mirror image, L-fructose, rotates the plane of polarization to the right. 

Ordinary tartaric acid, commonly present in grapes, is dextrorotatory and was long known as d- or dextro-tartaric acid. Its configuration has been established as HO H... 

This amine is of interest because it is readily resolved with tartaric acid to give the pure dextro and levo isomers.1... 

Pasteur.— The discovery that optically active substances exist in two forms dextro-rotatoryj and levo-rotatory and that the corresponding inactive compound is composed of equal amounts of the dextro and levo and may be split into these two forms, was made by Pasteur, who, because of his later remarkable work in the field of pathology, is not generally known as a chemist. Pasteur made this discovery during a study of tartaric acid, and it will be spoken of again when we come to that compound. 

One of the above formulas may be taken to represent the dextro form and the other the levo. The mixture of the two will produce the inactive acid. Now these three forms of tartaric acid are all known and they bear to each other exactly the same relation as has been explained in connection with lactic acid. The inactive form is able to be split into its two optical components like the inactive lactic acid. These three acids are as follows,... 

Dextro Tartaric Acid.—The ordinary tartaric acid as it occurs in grapes. 

It is this fourth unresolvable inactive tartaric acid which gives to tartaric acid its especial interest and importance in connection with the theory of stereo-isomerism. This acid, like the other three, has been fully explained in accordance with the tetra-hedral theory of van t Hoff and LeBel. The explanation rests upon the fact that there is a second asymmetric carbon atom in tartaric acid. We may construct, by models, or, by drawings, space-formulas for tartaric acid. According to the tetra-hedral theory, the dextro, levo and racemic inactive forms will be as follows, analogous to the corresponding formulas for the three lactic acids. The meso-tartaric acid is represented by the third drawing. 

The dextro tartaric acid has the three groups, (—COOH), (—OH), (—H) linked to each of the asymmetric carbons, arranged in a right handed manner in both of the asymmetric groups. The levo tartaric acid has, similarly, a left handed arrangement in both of the asymmetric groups. The racemic acid consists of equal molecules of these two active forms and is thus optically inactive and is able to be split into its optically 20... 

In 1820 Sir John Herschel, in considering the question of the different optical rotation of crystalline substances, suggested that it might be connected with an unsymmetrical form of crystallization. Later, Pasteur in 1848 while studying the salts of tartaric acid recalled this suggestion of Herschel and also a statement by Mitscherlich to the effect that the crystalline form of ordinary tartaric acid which is dextro rotatory is identical with that of racemic acid which is inactive. At that time the tw o tartaric acids just mentioned were the only ones known. 

Thus from a study of the crystalline sodium-ammonium salt of racemic acid and of dextro tartaric acid Pasteur showed, conclusively, the relationship of these two acids to each other and also discovered the existence of a third isomer optically active but of opposite direction to the ordinary tartaric acid already known. Racemic acid, therefore, is optically inactive because it consists of equal molecules of the ordinary dextro tartaric acid and the newly discovered levo tartaric acid. Also racemic acid can be resolved into its optically isomeric components by mechanically separating the two forms of crystals of the sodium-ammonium salt. The two active forms of tartaric acid, when mixed in equal molecular amounts, yield the inactive or racemic acid. Later, Pasteur prepared the fourth variety of tartaric acid, viz., meso-tartaric acid, by heating the cinchonine salt of dextro tartaric acid. This new acid proved to be inactive like racemic acid, but, unlike it, was unable to be resolved into optically active components. Its relation to the other three forms of tartaric acid was unexplained by Pasteur. 

Splitting Racemic Compounds.—The methods by which racemic compounds may be split into their optically active components are several. The three methods used were all originated by Pasteur. The first method has been referred to and consists of the mechanical separation of the two oppositely hemi-hedral forms in which the salts of a racemic compound crystallize. This method is especially applicable in the case of tartaric acid when the sodium-ammonium salt is used. The crystallization and separation must be carried out under definite conditions. If the racemic acid salt is crystallized below 28° the two forms of crystals are produced and a separation can be accomplished. If, however, the crystallization takes place above 28° the two forms of crystals are not produced but the sodium-ammonium racemate crystallizes in unseparable crystals of one form. That is, above 28° the sodium-ammonium racemate crystallizes as such, while, below 28° the racemate splits into its two isomeric components and equal amouts of the sodium-ammonium dextro tartrate and the sodium-ammonium levo tartrate are formed. The second method for the splitting of a racemic compound into its optically active components consists of the formation of the cinchonine, strychnine, or other similar alkaloid salts. When the cinchonine salt of racemic acid is formed it splits into the... 

Dextro tartaric acid is the ordinary tartaric acid as it is found widely distributed in nature, in grapes, mountain ash berries, pineapples, potatoes and other plants. It crystallizes without water of crystallization in transparent, mono-clinic columns which are easily soluble in water or in alcohol. 100 parts of water at 15° dissolve 132 parts of the acid. It melts at i68°-i70°. In water solution it is dextro rotatory. The chief source of tartaric acid is the juice of the grape, where it is present as the free acid and as the acid potassium salt. In this source it is mostly the dextro variety that is found. It is obtained from the vinasse, or residue which settles out from the juice after it has been expressed. When grape juice ferments, in the formation of wine, the solubility of the acid potassium salt is lessened due to the presence of alcohol and it gradually separates and settles to the bottom iii the form of what is known as lees. These lees are dried or recrystallized once and the product is then known as crude tartar or argol. The crude tartar contains, in addition to the acid potassium tartrate, free tartaric... 

Salts.—Several of the salts of dextro tartaric acid are important. 

Levo tartaric acid, the optical isomer of dextro tartaric acid, was discovered, as already stated, by Pasteur in 1848. It has the same solubility and melting point as the dextro acid. It crystallizes without water of crystallization in the form enantiomorphic to the dextro acid. Its optical rotation is the same in amount but opposite in direction to the dextro acid. When mixed in equal molecular amount with dextro tartaric acid it yields racemic acid. Its synthetic reactions have been considered. It has no common uses. 

German name, Trauben-saure, is derived from the word for grapes. It is probable that it does not exist in grapes as racemic acid but that it is formed from the dextro acid as this transformation can easily be effected by the action of acids or even by water alone. When tartaric acid is prepared synthetically from succinic acid, from glyoxal, or from malic, maleic or fumaric acids either racemic acid or meso-tartaric acid is always formed. That is, synthetic reactions result in the formation of an inactive form. The methods of splitting racemic acid into its optically active components has been fully discussed. The sodium-ammonium racemate is the only salt that is of importance. This has been spoken of in connection with the method of splitting racemic acid into its components.. Like the free acid this salt exists, in dilute solution, as equal molecular parts of the dextro and levo forms. Only in concentrated solution does it exist as the racemate itself. 

This acid, the inactive by intra-molecular compensation and un-resolvable into optically active components, was first obtained by Pasteur by heating the cinchonine salt of dextro tartaric acid, to 170 . It may also be prepared by boiling the dextro tartaric acid with an excess of hydrochloric acid, or with sodium hydroxide. Also by long boiling with water alone or by heating with a small amount of water to 165°. When di-brom succinic acid is treated with silver hydroxide, or when malic acid is oxidized, in the presence of water, both meso-tartaric acid and racemic acid are formed. When meso-tartaric acid is heated to 200° it is partly converted into racemic acid. Meso-tartaric acid crystallizes in rectangular plates with one molecule of water. The water free acid melts at i40°-i45°. 

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