227 



. while it was transformed into the acelyl-, benzoyl-, or benzyl i- 

 -<). Ti\- t iti\.s. HsrluT l ) observed that if trimcthyhnni. 

 with drxtro.^yratory ctltyl-x-bromo-propionate, the cthvl-trimclhylmni- 

 n<>- pro Donate produced racemises more repidly if the quaternary 

 amni<minin-s;ilt is present. Marckwald and Nolda 2 ) found that 

 d-iinivl-bnnnidc 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 Hoff. A rational explanation was suggested 

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

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

 form and vice versa are possible. Another explanation was given 

 by Werner 3 ), 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, 

 as already stated in the case of the complex chromi-oxalates. Nef 4 ) 

 sees a connection between the tendency for racemisation and the 

 binding and loosening of water-molecules from active organic mole- 

 cules containing hydroxyl-groups, under intermediate formation 

 of unsaturated compounds. 



By Von Halban 6 ), and by Frohlich and Wedekind 6 ), it has 

 been demonstrated by means of kinetic measurements, that in the 

 case of optically active derivatives of pentavalent nitrogen, auto-race- 

 misation is indeed intimately connected with an intermediate detach- 

 ment of groups, and successive recombination with the plurivalent 

 central atom. Here the active substance appears undoubtedly to be 

 decomposed into a tertiar amine and an alkyl-halogenide, until a 

 dynamical equilibrium is reached. It is easily understood therefore 



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



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



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



4) J. U. Nef, Ann. der Chemie 885. 191. (1904); Cf. also: O. Rothe, Ber. 

 d.d. Chem. Ges. 47. 843. (1914); P. Pfeiffer, ibid. 47. 1586. (1914). 



5) H. von Halban, Ber. d.d. Chem. Ges. 41. 2417. (1908); Zeits. f. Elek- 

 trochem. 18. 57. (1907). 



C) E. Wedekind and E. Frohlich, Ber. d.d. Chem. Ges. 88. 3438. (1906); 

 40. 1646 (1907); E. Wedekind and F. Paschke, Ber. d. d. Chem. G. 41. 

 2659. (1908). 



