130 MOLECULAR STRUCTURE 



or compound of the optical isomers. The equation to the 

 change is simplified on account of the similarity of the two 

 opposing reactions, for 



k = fc l} 

 whence 



dx . . 



Finally the behaviour of aceto-acetic ether, apparently due 

 to mutual transformation at ordinary temperatures, is most 

 peculiar. The phenomenon has been accurately studied, 

 especially by R. Schiff l . He concluded, on the ground of 

 the formation of the two isomers, 



H 3 CCOCHC0 2 C 2 H 5 H 3 CCOH = CC0 2 C 2 H 5 



| and 



C 6 H 5 CHNHC 6 H 5 C 6 H 5 CHNHC 6 H 5 



Melting point 78 Melting point 103 



with the aid of benzaniline, 



C 6 H 3 CH = NC C H 5 , 



that aceto-acetic ether is a mixture of two isomers : 

 H 3 CCOCH 2 C0 2 C 2 H 5 and H 3 CCOH = CHCO 2 C 2 H 5 , 



i. e. the keto- and enol-forms respectively. This view was 

 confirmed by the fact that different preparations did not 

 yield the isomeric benzaniline derivatives in the same 

 proportion; one obtained from Kahlbaum giving the pure 

 enol-form, another from Marquardt giving a mixture. 



The measurements of Traube 2 point to the same con- 

 clusion, indicating a slow change in the density : 



1-02443 ...... 15 minutes after distillation. 



1.02467 ...... 20 hours later. 



This went hand in hand with a change in the behaviour 



1 Berl. Ber. 31. 603. 



2 1. c. 29. 1715. See especially also Schaum, 1. c. 31. 1964. 



