Meso tartaric acid

The calcium salts, in particular that of meso-tartaric acid, separate very slowly, and the yield is appreciably lower if the mixture is allowed to stand only eighteen hours. 

The calcium salt of the principal product, d/-tartaric acid, crystallizes with four molecules of water, while the secondary product, meso-tartaric acid, forms a calcium salt which crystallizes with three molecules of water. The amount of sulfuric acid actually required may readily be calculated from the percentage of calcium found on analysis in the regular way or it may be estimated by igniting a sample, and titrating the residue with standard acid. 

Plane of symmetry in eclipsed conformation of meso-tartaric acid... 

Figure 9.11 A symmetry plane through the C2-C3 bond of meso-tartaric acid makes the molecule achiral. H ho co2h...

Let s return for a last look at Pasteur s pioneering work. Pasteur took an optically inactive tartaric acid salt and found that he could crystallize from it two optically active forms having what we would now call the 2R,3R and 2S,3S configurations. But what was the optically inactive form he started with It couldn t have been meso-tartaric acid, because meso-tartaric acid is a different chemical compound and can t interconvert with the two chiral enantiomers without breaking and re-forming chemical bonds. 

Meso compound A symmetrical compound containing two chiral centres configured so that the chirality of one of the centres is equal and opposite to the other. Such internal compensation means that these compounds have no overall effect on polarised light (e.g., meso tartaric acid). 

Tartaric acid (—)-Tartaric acid meso-Tartaric acid... 

This compound is optically active because of molecular asymmetry. Of course, the presence of an asymmetric carbon atom lends asymmetry to the molecule and hence gives rise to optical activity but it is not always essential. The presence of an asymmetric carbon atom may or may not give rise to optical activity. The case of meso. tartaric acid is worth mentioning in this connectiar. Although the molecule has two asymmetric carbon atoms but it is optically inactive. 

The fact that the existence of asymmetric C-atoms is neither necessary nor sufficient for chirality was pointed out in 1902 by Aschan 21> in his criticism of van t Hoff s concept. He used the examples of meso-tartaric acid 10 and the achiral trioxiglutonic acid 11 to demonstrate that asymmetric C-atoms are not sufficient for chirality, and example 72 shows that they are also not necessary. 

The equilibrium ensemble of the configurations of meso-tartaric acid 10 a—c has umin = 0. From the definition of umm follows immediately that for all achiral molecules min = 0 holds. This applies also to those cases where asymmetric C-atoms are present but cancel each other because of overall molecular symmetry. 

Meso-tartaric acid 10 has no element of chirality, because there is a conceivable conformation 10b with a mirror plane perpendicular to the central C—C-bond. 

Although the use of an epoxide hydrolase was already claimed for the industrial synthesis of L- and meso-tartaric acid in 1969 [51], it was only recently that applications to asymmetric synthesis appeared in the hterature. This fact can be attributed to the limited availabihty of these biocatalysts from sources such as mammals or plants. Since the production of large amounts of crude enzyme is now feasible, preparative-scale applications are within reach of the synthetic chemist. For instance, fermentation of Nocardia EHl on a 701-scale afforded > 700 g of lyophilized cells [100]). 

Cannabidiolic Acid dl- and meso-Tartaric acid Citric acid Diglycolic acid Iminodiacetic acid... 

Dihydroxybenzoic acid d-, dl-. and meso-tartaric acid Erythro- and t/irco-2-methyltartaric acid Meso- and f/jreo-2.3-dimethyltartaric acid... 

Problem 22.60 Which D-pentose is oxidized to an optically inactive dibasic acid and undergoes a Ruff degradation to a tetrose whose glycaric acid is meso-tartaric acid ... 

Structures 1 and 2 are enantiomers, and both are optically active. In structures 3 and 4, there is a plane of symmetry, i.e., there is a mirror image within a single molecule. Such a structure is called a meso structure. Structures 3 and 4 are superimposable, and essentially are the same compound. Hence, we have a meso-tartaric acid and it is achiral (since it has a plane of symmetry, and it is superimposable on its mirror image). Meso-tartaric acid is optically inactive. Therefore, for tartaric acid, we have (-f), (—) and meio-tartaric acid. 

Tartaric acid is dibasic (H2tart), carboxyl protons being ionized by pH 5. The hydroxyl groups are not ionized (p/Ca3 14 and pK 15.6).622 The formation constants of ( + )-,(-)-, ( )- and meso-tartaric acids with V02+ confirm binuclear complexes of optically active and, to a lesser extent, meso acids with V02+.623... 

Enantiomer recognition is a general principle in chemistry. Molecular recognition is achieved by numerous electronic and steric factors including chirality. This is also the case among molecules with the same atomic composition and connectivity. As illustrated in Scheme 27, chiral (/ ,/ )- or (5,5)-tartaric acid may be seen as a homochiral dimer of the / - or 5-pyramidal radicals, respectively meso tartaric acid is a result... 

The condition that makes possible the existence of meso compounds is an appropriate degree of molecular symmetry. There are several kinds of such molecular symmetry. In the case of projection formulas 25 (or 26) there is a plane of symmetry, which means that a plane can be placed through the molecule such that one half of the molecule is a mirror image of the other half The mirror plane for meso-tartaric acid can be seen easily from its projection formulas 25b and 26b. These two formulas are superimposable if one is rotated 180° in the plane of the paper. 

The Newman representation 25a or 26a of meso-tartaric acid does not have a mirror plane. Why is it different from the Fischer projections in this respect The reason is that the projection formulas represent a particular eclipsed conformation 27 of tartaric acid that does have a mirror plane ... 

The tetrose, D-erythrose, so obtained can be oxidized with nitric acid to meso-tartaric acid. Show how this information can be organized to establish the configurations of D-arabinose, D-ribose, ribitol, and D-erythrose. 

---