226 



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: d~^~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: 



dx 



31 = k (a x) k'x = k (a 2x), 



which on integration gives: 



N ln ^ = constant. 



t a2x 



From measurements made by Gadamer 1 ) on the racemisation- 

 velocities of hyoscyamine and of scopolamine under the influence 

 of sodium-hydroxide and of tr opine respectively, Herz 2 ) calculated 

 the racemisation-constants from this equation; he found for 

 hyoscyamine (at 5 C.) with sodium-hydroxide: 6,5. 10~ 3 , with tropine: 

 2,2. 10~ 2 ; for scopolamine with sodium-hydroxide: 0,77. 10~ 2 , and 

 with tropine: 1,9. lO" 2 at 2 to 4 C. 



Commonly racemisation is started by heating: the presence of 

 some other substances, be it as a solvent or not, often seems to 

 have an accelerating effect. Thus Jungf leisch 3 ) found, that tartaric 

 acid becomes more rapidly racemised if heated in the presence 

 of some aluminium-tartrate, than if heated alone. Often racemisation 

 occurs in an appreciable degree when a chemical reaction takes place ; 

 thus, for instance. Pope and Harvey 4 ) demonstrated that dex- 

 trogyratory a-c-tetrahydro-fi-naphtylamine became partially race- 



1) J. Gadamer, Archiv der Pharmac. 239. 294. (1901). 



2) W. Herz, Jahrber der Schles. Ges. fur vaterl. Kultur, Mai 1911. 



3) E. Jungfleisch, Compt. rend, de 1'Acad. d. Sc. Paris 85. 805. (1877). 



4) W. J. Pope and A. W. Harvey, Journ. Chem. Soc. London 79. 74. (1901); 

 Proc. Ch. Soc. 16. 74, 206, (1890). 



