Racemic and Mesotartaric acid

201 Hollemann, Rcc. trav. chim. Pays-Itins, 

Boil the tartaric acid and caustic soda solution for three hours in a round flask (I litre), or preferably in a tin bottle furnished with reflu. condenser. The use of a tin vessel obviates certain clitli-cultiesof filtration which the solution of the silica by the action of the alkali on the glass entails. The liquid, after boilinjg, is carefully neutralised with cone, hydrochloric acid (it is acl is-able to remove a little of the solution beforehand in case overshooting the mark) and an excess of calcium chloride solution is added to the hot liquid. The mixture is left overni hl. and the calcium salts filtered off at the pump, washed with water, and well pressed. 

The last mother liquors contain mesotaitanc acid, in. p. 1.4. 3 144°, which is much more soluble in water than racemic ju ici. To obtain a pme specimen repeated crystallisation is necesstiry. 

The yield varies with the period of boiling, but usually does not exceed to grams. 

Resolution of Racemic Acid.—The racemic acid is dissolved in water (250 c.c.) and divided into two equal volumes. Half of the solution is carefully neutralised with caustic soda and the other half with ammonia, and the two solutions then mixed. 

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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 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. 

Anschutz then supposed that Fittig s formula for maleic acid might be assigned to fumaric acid but the relations to racemic and mesotartaric acids excluded it, and he formulated maleic acid as (VI), which does not contain a carboxyl group. 

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