Absolute Asymmetrie Synthesis and Asymmetrie Catalysis 161 



but it must have a dissymmetric structure. Cases have been described in which 

 all three forms of such complex-formers were used. 



For the resolution of esters of hydroxy acids Cramer [33] used a crystaUine 

 inclusion complex with cyclodextrin. The resolution amounted to 16%. For the 

 resolution of see.-hutyl bromide, Powell [34] used triorthothymotide, which 

 crystaUizes as a racemate without forming enantiomorphic crystals, but which 

 easily gives rise to inclusion complexes. 



Schlenk [35] gave an example of the use of an optically inactive adsorbent — 

 crystals of urea — which have a spiral structure, similar to that of quartz, and 

 which easily form inclusion complexes. When racemic 2-chloro-octane is crystal- 

 hzed with urea 95-6% resolution is achieved. 



Quartz occupies an important position in hypotheses concerning the appear- 

 ance of the first optically active substances, by virtue of its being a dissymmetric 

 adsorbent. 



Owing to its dissymmetrical lattice, quartz manifests considerable selectivity 

 in the adsorption of compounds with molecular or crystalline dissymmetry. The 

 selective adsorption on quartz of galactose and arabinose is well known [36]. It 

 is foimd that there is epitaxy of hemihedral crystals of glycine, alanine and 

 glutamic acid on d- and L-quartz [37]. 



The selective adsorption of antipodes on quartz for the purpose of resolving 

 racemates does not show a high specificity. Thus, attempts to resolve p-pheny- 

 lenebisiminocamphor have been unsuccessful [24] while the degree of activation 

 of racemic butan-2-ol and the differential adsorptive capacity of d- and L-quartz 

 for (— )-2-methylbutan-i-ol was insignificant [38]. 



In spite of the low selectivity of the adsorption of antipodes of a number of 

 metaUic complexes, this method has had a certain appHcation in the estabhsh- 

 ment of their structure. A number of cases are known of the selective adsorption 

 of one antipode of a complexes of chromium or cobalt on L-quartz [39, 40], as 

 well as the partial resolution of racemic complexes of chromium, cobalt and 

 platinum [41, 42]. 



Quartz plays an incomparably more important part as a carrier of catalysts, 

 with the help of which one may carry out absolute asymmetric syntheses, 

 thereby imitating enzymic activity. 



2. ASYMMETRIC CATALYSIS 



Enzymes and Chemical Models of Enzymes 



Practically all vitally important processes are brought into being by the in- 

 fluence of enzymes — dissymmetric formations — the mechanism of their stereo- 

 specific action being, for the most part, still obscure. Therefore, in trying to 

 find out the subtle w-ays in which these catalysts act, great interest attaches to 

 attempts to produce dissymmetric inorganic and organic catalysts, i.e., chemical 

 models of enzymes. This is valuable, both for the elucidation of the stereospeci- 

 ficity of enzymes, and for an understanding of the mechanism of asymmetric 

 catalysis, which plays a great part in the production and development of dis- 

 symmetry in the organic world. 



II 



