X. A, 1 Gibbs and Brill: Diethylsuccinosuccinate 55 



ethylsuccinosuccinate does not. Mixtures of the two compounds 

 melt at 166°. It is possible that this is the reduced ethylsuc- 

 cinosuccinate of the following constitution : 



H COOEt 



H2— ^ y-OR 



HO' 



./\/-«^ 



H COOEt 



The absorption spectrum shows some differences from the 

 known diacetyl derivative. It was observed that the crystals 

 of diethylsuccinosuccinate which form on cooling the filtrate 

 obtained after the reduction with zinc dust and hydrochloric acid 

 are more yellow than the original compound employed. This 

 may indicate that the enol form is more readily reduced, the 

 keto form remaining in a greater proportion than was orig- 

 inally present. 



Absorption spectra. — The absorption spectra of two samples 

 of ethylsuccinosuccinate, one 90 per cent enol melting at 127" 

 and the other practically all keto melting at 123°, in neutral 

 alcohol solution and with 2 equivalents of sodium ethoxide, and 

 the diacetate of ethylsuccinosuccinate are plotted in fig. 1. 



It is to be noted that the absorption band heading at 1/A=2,660 

 in neutral solution is more persistant in the keto form, while 

 in alkaline solution the reverse is the case. This points to the 

 conclusion that the color is due to the keto form and that this 

 compound is less affected by alkalies. The curve of the acetyl 

 derivative shows no absorption band and leads to the conclu- 

 sion that the labile hydrogen of the hydroxyl is necessary to 

 selective absorption. The shift of the band produced by sodium 

 ethoxide is found in all hydroxy benzene derivations examined.^' 



The absorption curve of the diimide ^'' of ethylsuccinosuccinate 

 in neutral solution and in the presence of an excess of hydro- 

 chloric acid are plotted in fig. 2. 



Since this compound is a derivative of the keto fonn in which 

 the oxygen atoms are replaced by the more active =NH groups, 

 it is to be expected that it will be more highly colored than the 

 keto ethylsuccinosuccinate and show a greater absorption band 

 in the same region of the spectrum. Acids form salts with this 



"Gibbs and Pratt, This Journal, Sec A (1913), 8, 33. 

 "Baeyer, Ber. d. deutschen chem. Ges. (1886), 19, 429. 



