Mesotartaric acid

Colourless prisms m.p. 130 C. Manufactured by treating maleic anhydride with water. It is converted to the anhydride by heating at By prolonged heating at 150 "C or by heating with water under pressure at 200 C, it is converted to the isomeric (trans) fumaric acid. Reduced by hydrogen to succinic acid. Oxidized by alkaline solutions of potassium permanganate to mesotartaric acid. When heated with solutions of sodium hydroxide at 100 C, sodium( )-malate is formed. Used in the preparation of ( )-malic acid and in some polymer formulations. 

Racemic acid, ( )-tartaric acid, is a compound of the two active forms. M.p. 273 C (with IHjO), m.p. 205°C (anhydrous). Less soluble in water than (-t-)-tartaric acid. Formed, together with mesotartaric acid, by boiling (4-)-tartaric acid with 30% NaOH solution, or by oxidation of fumaric acid. Potassium hydrogen racemate is very insoluble. 

Mesotartaric acid crystallizes in plates (IHjO), m.p. 140 C (anhydrous). Very soluble in water. Obtained from the mother-liquors in the preparation of racemic acid or by oxidation of maleic acid. Potassium hydrogen mesotartrale is soluble in water. 

Racemic and Mesotartaric Acids.—These two acids represent two inactive types of compounds containing a< yminct7 ic carbon atoms (see above). Apart from certain well-marked differences in physical properties they also differ in one important feature racemic acid can be lesoh-ed into its optical enantiomorphs, whereas mesotartaric acid cannot. The latter belongs to what is termed the inactive indivisible type. If we examine the structuial formula of tartaric acid it will l>e seen that it possesses two asyimnetric carbon atoms, denoted in the formula by thick type. 

The oxidation of maleic acid by KMn04 gives mesotartaric acid. 

We have already seen that mesotartaric acid is optically inactive because of internal compensation, although, it contains two asymmetric carbon atoms. We have also seen that the molecule as a whole must be asymmetric for being optically active. Therefore, the best criterion to judge optical activity would be whether molecule is superimposable on its mirror image or not. Now superimposability would lead to optical activity and vice-versa and non-symmetrical molecules are non superimposable. To decide whether a molecule is symmetrical or not, we should first try to know whether it has a plane of symmetry, a centre of symmetry or an alternating axis of symmetry. The presence of any one of these would lead the molecule to be symmetrical and hence to optical inactivity. 

Let us consider a molecule of the type C abd - C abd (exemplified by mesotartaric acid) which has got a plane of symmetry shown by the dotted line. 

The conversion of an optically active compound into an optically inactive mixture (dl mixture) is known as racemisation. The (+) and (-) forms of most compounds are capable of racemisation under the influence of heat, light or chemical reagents. Which agent can bring about racemisation, depends on the nature of the compound. For example (+) tartaric acid when heated strongly with water to 175° is transformed into a mixture of racemic and mesotartaric acids. 

Oxidation of maleic acid by NaC103-0s04 in aqueous solution involves the formation of the cyclic osmate ester, the oxidative clevage of which by chlorate gives mesotartaric acid with the regeneration of 0s04. 

What are the products of oxidation and reduction of the monosaccharides Mucic add, of which the preparation from d-galactose has been described, is optically inactive and incapable of resolution, just like duldtol, the corresponding hexahydric alcohol. As the formula shows, the four asymmetric carbon atoms of galactose form two pairs (2, 5 and 3, 4) having the same substituents but opposite arrangement in space, and when the carbon atoms 1 and 6 become alike, inactive forms are produced by intramolecular compensation, as in mesotartaric acid. 

Certain chiral APIs, however, are diastereoisomers and mesocompounds with two or more optically active centers (carbons) in the molecule (i.e., eryth-rose, threose, and mesotartaric acid). In such cases, simplification between race-mates and single enantiomers is often not readily apparent. The conversion of racemates to active enantiomers can be accomplished using one of the following reaction pathways ... 

It appears that the CHOH-COOH group, or the CO-COOH group, promotes adsorption on the lactic acid centre, while the CH2-COOH group favours adsorption on the succinic acid centre. An exception was found in mesotartaric acid, HOOC CHOH CHOH-COOH, which seems to be adsorbed on both centres and the phenyl propionic acid had some tendency to be adsorbed on the lactic acid centre also. 

Problem 34.17 Give the specification by the R/S system of (a) (-j-tartaric acid (b) (4-)-tartaric acid (c) mesotartaric acid. 

The nomenclature of optically active organic molecules has been revised since their absolute configuration has been determinable via X-ray diffraction (Chapter 6). The equivalent terms are (d)-tartaric acid = (-l-)-tartaric acid = (2R,3R)-tartaric acid (/)-tartaric acid = (—)-tartaric acid = (2S,3S)-tartaric acid mesotartaric acid = (2R,3S) tartaric acid = (2S,3R)-tartaric acid. 

It is easy to imagine a T5T>e A 2 crystal structure for KHY centro-s3mimetric hydrogen-mesotartrate anions linked into chains by hydrogen bonds across centres of symmetry. In fact, neither mesotartaric acid nor its anion adopts a centrosymmetric conformation in any of the... 

Sodium chlorate in dilute acid with OsOt catalyst.Mesotartaric acid... 

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