Tartaric acid, occurrence

Tartaric acid is noteworthy for a) the excellent way in which the majority of its salts Crystallise, and h) the frequent occurrence of salts having mixed cations. Examples of the latter are sodium potassium tartrate (or Rochelle salt), C4H40 NaK, used for the preparation of Fehling s solution (p. 525), sodium ammonium tartrate, C4H OaNaNH4, used by Pasteur for his early optical resolution experiments, and potassium antimonyl tartrate (or Tartar Emetic), C4H404K(Sb0). The latter is prepared by boiling a solution of potassium hydrogen tartrate (or cream of tartar ) with antimony trioxide,... 

Occurrence. (R-R, R )-Tartaric acid occurs in the juice of the grape and in a few other fmits and plants. It is not as widely distributed as citric acid or S(—)-mahc acid. The only commercial source is the residues from the wine industry. (i -R, R -Tartaric acid has been found in the fmit and leaves of BauMma reticulata, a tree native to MaU (western Africa). Like the dextrorotatory acid, it forms anhydrous monoclinic crystals. 

One of the earhest known examples of racemization was described by Pasteur in his studies of tartaric acid, By heating D-tartaric acid to 165°C in water lie partially converted it into a mixture of D-, L- and fnejo-tartaric acids. The occurrence of some DL-tartaric acid along with the natural D-tartaric acid in the wine industry is explained on the basis of partial racemization,... 

Add 0.1 M tartaric acid in the following portions 4x5 ml, 10 x 1 ml, 4x5 ml. Allow the potential of the GC/PANI electrode to stabilize between each addition. Recording of the titration curve in this manner takes ca. 2 h. An example of the titration curve is shown in Fig. 5.2. The occurrence of a potential maximum at 5-10 ml and the minimum at 15 ml tartaric acid indicates where precipitation of trimeprazine tartrate starts. The increasing potential around 25 ml tartaric acid indicates the equivalence point. Titration of 1.4 M trimeprazine base with 0.7M tartaric acid results in a larger potential change at the equivalence point, as can be seen in Fig. 5.3. 

Properties.—Succinic acid has been known for a long time. It is quite widely distributed in nature. It is found in unripe fruits, especially in grapes, also in lignite, in peat and in many plants. Its most important occurrence is in amber from which it may be obtained by distillation. It is also a constituent of wines where it is the product of the alcoholic fermentation of the sugars of grape juice. Another source, which will be considered later, is from malic and tartaric acids by bacterial or mould fermentation. Succinic acid crystallizes in plates or columns which melt at 182°. It sublimes when it is heated below its melting point. When heated rapidly to 235° it loses water and forms an anhydride. It is soluble in 14 parts of water. 

The occurrence of some DL-tartaric acid along with natural D-tartaric acid in the wine industry is explained on the basis of partial racemization. The L-form is the commercial product. 

Addition of a small proportion of iron (II) sulfate to D-tartaric acid-hydrogen peroxide causes rapid conversion into a product closely related to dihydroxymaleic acid. Occurrence of a reaction with substituted hydrazines indicates the presence of a keto acid (1), and isolation of a diacetate and a dibenzoate favors the hypothesis of formation of dihydroxy-fumaric acid (2). On the basis of pH studies, Hatcher and Sturrock ... 

The occurrence of the above redox reaction and hence the presence of tartrate is signalled by the fact that the silver oxide is dissolved on the addition of concentrated ammonium hydroxide whereas any elementary silver remains behind as a black powder. If very small amounts of tartaric acid are to be detected, it is advisable to conduct a comparison test on a blank. 

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