Eutectic point, mandelic acid

Sublimation. Such effects can also be seen in solid-gas interphase. Scheme 30 shows the consequences of fractional sublimation of partially resolved L-mandelic acid (47). The optical purity could be enhanced or reduced, depending on the optical purity of the starting material. Since the eutectic point of mandelic acid is obtained with about a 75 25 enantiomer ratio, such a mixture is more readily sublimed than the racemate or conglomerate. Scheme 30 gives other examples of optical enrichment by sublimation. Phenyl 1-phenyl-1-propyl sulfide in 6% ee affords the sublimed compound in 74% ee, but the residue is... 

The solubility curves of mandelic acid have eutectic points between the chiral and the racemic compound. At atmospheric pressure, the eutectic conq>osition is almost constant regardless of temperature, while the solubility varies according to the temperature. So, it is hard to separate the chiral crystal from the feed when the con )osition is between the eutectic and the racemic conq>osition. 

These results indicate that the mother liquor of saturated mandelic acid solution may coexist with both L-form crystals and the racemic crystals, when feed C was pressurized in the vessel for crystallization. The coexistence of the chiral and the racemic indicates that the conqx)sition of the solution was the eutectic. So, the solubility and the L-form connposition of mandelic acid in the mother liquor represents the eutectic points of mandelic acid under pressure (see the arrow from point C in Fig.5). 

For a simple eutectic and a racemic compound-forming system in Figure 3.30, the measured ternary phase diagrams of the amino acid threonine and the fine chemical mandelic acid, both in water as solvent, are exemplarily shown. The diagrams contain equilibrium data measured in isothermal experiments as described in Section 3.3.5.2. Different temperatures were applied. All solubihties are related to the solid phases given, no solvate was found. Most points measured refer to... 

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