362 PROCEEDINGS OP 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 jjrove 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 j3 brompyromucic acid in its jmysical properties, although 

 its melting point, 145-146°, is comparatively high. It is to be noted, 

 however, that the f3y dichlorpyromucic acid alone is formed by the 

 action of alkalies upon the ethyl pyromucic 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 

 \ 





 / 



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 /?y and ft8 positions 

 respectively, and that pyromucic acid itself probably had the formula 



HC = C - COOH 



O 

 / 

 HC = CH. 



The structure of the fSy and /?S 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 8 position, or that it must be a geometrically isomeric form of 

 the (38 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. Tonniesf had shown that 8 brom- 



* These Proceedings, xxi. 182. 

 \ t Berichte de deutsch. chem. Gesellsch. 



