The Role of Dissymmetry 99 



Soret [14] observed that crystallization of sodium chlorate in the air led to the 

 formation, mainly, of the (— )-enantiomorph while, when the crystallization took 

 place in sealed tubes the (+)-form separated in 433 cases, the (— )-form in 411 

 cases while in 43 cases a mixed form was produced. However, if the necessary 

 precautions are taken, this method gives satisfactory results. 



Thus, by priming with crystals of one antipode it has been possible to separate 

 the racemic forms of zinc and ammoniimi lactates [15], phenylbenzylhydrazone 

 of erythrose [16] and Co- and Cr-oxalatobisethylenediamine [17]. 



In 1934, Calzavara [18, 19] took out a patent on the separation into antipodes 

 of racemic adrenaline and other alkaloids. This was the method by which 

 Velluz et al. [20] resolved racemic rÄreo-i-A''-nitrophenyl-2-aminopropane- 

 I : 3-diol. 



The selective crystallization brought about by the introduction into a super- 

 saturated solution of racemate of crystals of one antipode or other crystals iso- 

 morphous with it has been studied in detail by Ostromyslenskii [21]. It was 

 found that, from a supersaturated solution of sodium ammonium tartrate one 

 antipode would crystallize out in the presence of not only the (+)- or (— )- 

 tartrate but also when isomorphous or isodimorphous crystals were added. Thus, 

 the introduction of L-asparagine evoked the crystalHzation of (+)-tartrate. Even 

 such compounds as glycine, which are not composed of dissymmetrical molecules 

 but form enantiomorphic crystals can evoke the crystallization of one isomer 

 from a solution of racemate of asparagine or sodium ammonium tartrate. In 

 the presence of crystals of sodium nitrate one enantiomorph always crystallizes 

 out from aqueous solutions of sodium periodate [22] sodium silicotimgstate [23] 

 or guanidine carbonate [24]. Zelinskii [24] achieved the separation of enantio- 

 morphs during the crystallization of dimethyldihydroxyglutaric acid. 



Enantiomorphic substances in nature are almost always found in the separate 

 crystalline state, their crystaUine racemates are extremely rare. It is thus quite 

 possible that locahzed asymmetric synthesis could take place on such inorganic 

 and organic dissymmetrical crystals. 



3. Spontaneous crystallization. On evaporation, concentrated solutions of 

 acid ammonium malate deposit crystals which show optical acitivity. Van't HofF 

 & Dawson [25] showed that these crystals consist of three parts of the (+)- and 

 one part of the (— )-salt. Malic acid may be obtained in an optically active form 

 by the spontaneous crystallization of a salt of composition C4H605,2Mo03,2NH3 

 [26]. 



The spontaneous crystallization of sodium tartrate and sodium ammonium 

 tartrate has been thoroughly studied. Other known cases of spontaneous reso- 

 lution of racemates concern asparagine [27], methoxy-4-methyldeoxybenzoin 

 [28], dibenzalpentaerythritol [29] and erjnJiritol [30], dilactylamide [31], the 

 lactone of gulonic acid [32], camphoric [33] and glutamic acids [10, 36], complex 

 salts of cobalt and rhodium [34], /3-decalol [35] and zVohydrobenzoin [36]. 



Neuberg [37] found that, when it has been kept for a long while in a solution 

 of potassium salts, /3-methylvaleric acid deposits crystals of the (+)-acid of a 

 high degree of purity. After keeping a solution of methylethylallylphenyl- 

 ammonium iodide in a sealed ampoule for some months, Havinga [38] observed 



