234 



The phenomenon mentioned is, as already said, called racemisation 

 or auto-racemisation l ). It can also be a serious obstacle in the 

 'attempts to produce the optical antipodes from a racemoid, and it 

 may be the cause of 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 2 ), could be demonstrated, among other 

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

 succinic acid 3 ). Walden found, for instance, that dextrogyratory 

 dimethyl-bromo-succinate lost its activity at ordinary temperatures 

 in about four years, the dextrogyratory isobutyl-bromo-propionate 

 and the corresponding methyl-phenyl-bromo-acetate in three years, 

 while in the case of the ethers of hydroxy- or chloro-acids, the auto- 

 racemisation took place much less rapidly. At higher temperatures 

 the process is appreciably accelerated. 



Because the system no longer alters with varying temperature, 

 when optical ^activity is once established, the heat-effect of the 

 change of an atomistic configuration into its enantiomorphous one 

 must be zero. There is, moreover, every reason to suppose, that in the 

 reversible reaction: dr^l, the velocity-constants k and k' of both 

 opposite changes are equal. The kinetic equation, expressing the 

 relation between the time t elapsed and the quantity transformed, 

 may be written: 



//r 



- = k (ax) k'x = k (a2x), 



which, on integration, gives: 



In- 

 t c 



From measurements made by Gadamer 4 ) on the racemisation- 



j , a 



In ^= constant, 

 t a 2x 



l ) A rigorous distinction between racemisation and autoracemisation can 

 npt be made. 



2 \ J. A. Le Bel, Compt. rend., 87, 213, (1878); Bull, de la Soc. Chim., (2), 

 31, 104, (1879); J. Lewkowitsch, Ber. d. d. Chem. Ges., 15, 1505, (1882); cf. 

 also: A. F. Holleman, Receuil des Trav. d. Chim. d. Pays-Bas, 17,323, (1918); 

 A. MacKenzie and H. Wren, Journ. Chem. Soc., 115, 602, (1919); etc. More 

 especially the influence of hydrolysis by alkalies is concerned here. 



An exhaustive review of the phenomena of auto-racemisation has been given 

 by P, Walden, in his book: Optische Umkehr-Erscheinungen, Braunschweig, 

 (1919), page 160183. 



3) P. Walden, Ber. d. d. Chem. Ges., 31, 1416, (1898). Cf. also: J. H. Van 

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



4 ) J. Gadamar, Archiv der Pharmacie, 239, 294, (1901). 



