235 



velocities of hyoscyamine and of scopolamine under the influence 

 of sodium-hydroxide and of tr opine respectively, Herz *) 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. 1(H 2 ; for scopolamine with sodium-hydroxide: 0,77. 10~ 2 , and 

 with tropine: 1,9. 10~ 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 Jungfleisch 2 ) found, that tartaric 

 acid becomes more 'rapidly racemised if heated in the presence 

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

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

 thus, for instance, Pope and Harvey 3 ) demonstrated that dex- 

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

 mised, while it was transformed into the acetyl-, benzoyl-, or benzyli- 

 dene-deriva.tives. Fischer 4 ) observed that, if trimethylamine reacts 

 with dextrogyratory ethyl-u-bromo-propionate, the ethyl-trimethylami- 

 no-propionate produced racemises more rapidly, if the quaternary 

 ammonium-salt is present. Marckwald and No Id a 5 ) found that 

 d-amyl-bromide is much more rapidly racemised if silver-acetate 

 be present, than if this is not the case. 



The process of autoracemisation is very difficult to explain from 

 the standpoint of the doctrine of directional valency-unities, as 

 proposed by Van 't Hof f. A rational explanation was suggested 

 in some cases by supposing intermediate tautomeric changes, e. g. 

 in the cases where transitions from the "ketonic" into the "enolic 

 form and vice versa are possible. Another explanation was given 

 by Werner 6 ), fitting in with his views on valency and affinity, 

 by supposing a gradual increase of the amplitude of vibrating radicals 

 round their equilibrium-positions in space, if the temperature 

 becomes higher. 



The consequent influence of the solvent can hardly be doubted, 



!) W. Herz, Jahresber. der Schles. Ges. fur vaterl. Kultur, Mai 1911. 



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



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

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



4 ) E. Fischer, Ber. d. d. Chem. Ges., 40, 5000, (1907). 



5) W. Marckwald and E. Nolda, Ber. d. d. Chem. Ges., 42, 1583, (1909). 



6 ) A. Werner, Beitrage zur Theorie der Affinitat und Valenz, Zurich, (1891); 

 cf. also: P. W a Id en, Optische Umkehr-erscheinungen, loco cit. 



