Resolution of Optically Stable Racemates

The above work on optically selective adsorption has a close bearing on an earlier observation by Schwab and Rudolph (128a) that, when 2-butanol is catalytically dehydrated over active quartz, the unchanged alcohol is found to have developed an optical rotation. This is apparently due to an optically selective adsorption of (-I-) or (—) 2-butanol on the enantiomorphous crystals of the catalyst. 

An unusual type of optical activation recorded by McKenzie (81) may be considered here. It was found that, when dl-tartaric acid is neutralized with one molecular proportion of caustic potash, and one molecular proportion of (—)-malie add is added to the solution, a mixture of dl and (-h) tartrates crystallizes out a dmilar though less pronoimced activating effect has more recently been oteerved with (-f-)-citramalic acid (2). While suggesting very tentatively that these effects might be considered examples of asymmetric induction, McKenzie at the same time pointed out that they might also be due to an unusual partial resolution of a racemic acid by an optically active add, due to physical differences between a pair of diastereoisomeric double salts. The latter explanation is perhaps the more likely. 

Methods of separating diastereoisomerides other than by fractional crystallization have been developed compa,ratively recently. Fractional distillation has been successfully applied by Bailey and Hass (7), and fractional distribution between immiscible solvent pairs by Shapiro and Newton (129). Fractional adsorption on symmetrical adsorbents such as silica gel and carbon has also been achieved, chromatographic methods with solutions having been applied by Jamison and Turner (55) and Hass, de Vries, and Jaff6 (44), while Isom and Hunt (49) have noted fractional adsorption from the gaseous phase. 

and Bamann (147), and many other workers, have recorded similar results with a variety of different esterases. 

---

The classification rests on the recognition of the four broad categories (A) resolution of optically stable racemates, (B) optically selective inversion of configuration in optically labile racemates, (C) optically selective synthesis of new centers of dissymmetry, and (D) optically selective inactivation of existing centers of dissymmetry. 

---