(*S*>*R*)-**FTHQ**

#### **2.1.2 Partial crystallization, distillation**

When a part of an enantiomeric mixture is transformed into a crystalline salt and the residue can be distilled, the solid phase may contain either the racemic composition or the excess of the enantiomer. In the former case the distilled fraction should be the enriched mixture relative to *ee*0, but the less pure mixture can be found in the distilled fraction when the *ee*0 > *ee*Eu. This is applied even if the salt of the enantiomeric excess proportion is the more stable, as well. An example for this phenomenon is the purification of the enantiomeric mixture of phenylethylamine (**PEA**). The mixture was treated with less than an equivalent amount of dicarboxylic acid (oxalic acid, succinic acid, fumaric acid or phthalic acid = **DCA**) (see Table 1, the molar ratio: **PEA**/**DCA**~ 3,3/1,25), and the excess of the amine was distilled. The **PEA**-**DCA** salt behaved as a racemate because eedeszt > ee0 In case of the salts of oxalic- and malonic acids this is changed above of eutectic composition.23


Table 1. The enrichment of enantiomeric mixtures of (R>S) – **PEA** via partial salt formation followed by distillation.
