362 PROCEEDINGS OF THE AMERICAN ACADEMY 



the solubility of their salts show their close relationship to these bro- 

 mine derivatives, while the products formed from them by oxidation 

 conclusively prove that they are structurally isomeric, and that the 

 chlorine atoms occupy the same relative position that the bromine 

 atoms hold in the dibrompyromucic acids. On reduction these two 

 acids both yield the same chlorpyromucic acid, which in its turn closely 

 resembles the y3 brompyromucic acid in its physical properties, althougli 

 its melting point, 145-1-4(3°, is comparatively high. It is to be noted, 

 however, that the (iy dichlorpyromucic acid alone is formed by the 

 action of alkalies upon the ethyl j^yromucic tetrachloride, while the two 

 isomeric dibrompyromucic acids are simultaneously formed under sim- 

 ilar conditions. This simultaneous formation of the two structurally 

 isomeric acids from pyromucic tetrabromide to which the formula 



Br Br 

 H - C - C - COOH 

 \ 



O 

 / 



HC - C - H 

 , Br Br 



may be assigned led Hill and Sanger * to the conclusion that these 

 acids must have their bromine atoms in the ySy and /3S positions 

 respectively, and that pyromucic acid itself probably had the formula 



HC = C - COOH 



O 



/ 

 HC = CH. 



The structure of the ySy and /38 dichlorpyromucic acids seems to us 

 to be thus sufficiently established. 



As to the third isomeric form, which for the present we have called 

 the X dichlorpyromucic acid, since it gives chlorfumaric acid by oxida- 

 tion, it is evident that it must either have its chlorine atoms in the 

 y and S position, or that it must be a geometrically isomeric form of 

 the /3S acid. Unfortunately, we have been able to obtain as yet no 

 evidence which conclusively proves either view to be correct. A 

 dichlorpyromucic acid having its chlorine atoms in the y and 8 posi- 

 tions could not well be formed from ethyl pyromucic tetrachloride by 

 the simple loss of hydrochloric acid, Tonnies t had shown that 8 brom- 



* These Proceedings, xxi. 182. 

 \ t Berjchte de deutsch. chem. Gesellsch. 



