225 



Werner 1 ) observed that tris-x-dipyridyl-ferro-salls of the type: 



[Fe(Dipyr) 3 }X 2 , 



lose half of their original, very high rotatory power in about half 

 an hour ; in the case of the carbonato-di-ethylenediamine-cobalti-s&lts 2 ) : 



Co 



it diminishes in about eight days and at room-temperature, to 

 half its original value, while at 90 C. it is destroyed completely in 

 a very short time. Also the complex chromi-tri-oxalates*): 



lose their rotatory power rather rapidly, in aqueous solution much 

 faster than in a mixture of acetone and water. 



Undoubtedly the mechanism of this reaction includes an interme- 

 diate stage of temporarily detaching of the groups from the central 

 metal-atom. The already mentioned tri-ethylenediamine-cobalti- , and 

 the corresponding rhodium-salts however, can be boiled in solution 

 without the rotatory power of it perceptably diminishing. 



On closer examination it is found that the phenomenon described 

 is really connected with the reaching of a state of equilibrium between 

 the two enantiomorphously related molecules in the solution, equili- 

 brium being arrived at if the molecules of both components be 

 present in equal number. 



The phenomenon mentioned is called racemisation or auto-race- 

 misation*'). It can be also a serious obstacle in the attempts to 

 produce the optical antipodes from a racemoid, and give many 

 difficulties during the study of optically active substances. 



That this is really a case which is wholly comparable with other 

 cases of thermal equilibrium 5 ), could be demonstrated, among other 

 ways, by the auto-racemisation of the ethers of optically active bromo- 

 succinic acid 6 ). Walden found for instance, that dextrogyratory 



1) A. Werner, Ber. d. d. Chem. Ges. 45. 434. (1912). 



2) A. Werner and Mac Cutcheon, Ber. d. d. Chem. Ges. 45. 3283. (1912). 



3) A. Werner, Ber. d. d. Chem. Ges. 45. 3065. (1912). 



4 ) A rigorous distinction between racemisation and auto-racemisation can 

 not be made. 



6) J. A. Le Bel, Compt. rend. 87. 213. (1878); Bull. d. 1. Soc. Chim. (2). 

 81. 104. (1879); J. Lewkowitsch, Ber. d. d. Chem. Ges. 15. 1505. (1882). 



6) P. Walden, Ber. d. d. Chem. Ges. 81. 1416. (1898). Cf. also: J. H. Van 

 'tHoff, Vorles. ii. theor. u. phys. Chemie //. p. 122. (1899). 



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