Resolving agents acidic

It is an attractive resolving agent, because it is relatively inexpensive and commercially available on a ton scale for industrial applications. One of the remarkable properties of (-)-DAG, which other acidic resolving agents lack, is its water-insolubility. This feature permits the recovery of the resolving agent in a simple and efficient manner. 

Troger s base, the resolution of which with a strongly acidic resolving agent is accompanied by a crystallization-induced asymmetric transformation (also see p426)87. 

Typical resolving agents are summarized in Table 4. Typical acidic resolving agents from natural products are malic acid, tartaric acid and its derivative, camphor sulfonic acids derived from camphor. 10-Camphor sulfonic acid is a strong acid and indicates high capability of making salts with weak bases. 

Tartaric acid (9) is the most conventional acidic resolving agent for basic race-mates. A great number of basic racemates have been resolved by 9 so far. In Nature, the L-form (+)-d-form is abundant and occurs in many fruits. However, not only the L-isomer but also the D-isomer are commercially available in fairly low costs. This makes the availability of this acid notable. 

When water is used as a solvent, an acidic resolving agent is favorably recycled as an aqueous solution in an industrial-scale operation. However, the presence of NaCl in the aqueous solution cannot be avoided. This arises from the decomposition of the corresponding less-soluble salt with aqueous NaOH to liberate the resolved amine, followed by neutrahzation with aqueous HCl. Therefore, the enantioseparations were performed in the presence of NaCl to check the possibility of recovering the resolving agent as an aqueous solution. The coexistence of NaCl up to 12% in the aqueous solution did not affect the yield and total resolution efficiency with retention of diastereomeric purity (100%), but when the NaCl concentration... 

The equilibrium model of a resolution of DL racemic base with an acidic resolving agent (RH) can be outlined bellow. 

Figures 1.38 and 1.39 illustrate selected commercially available basic and acidic resolving agents, commonly used just as examples of the many now available for the resolution of racemic acids and bases respectively.

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