152 PROCEEDINGS OP THE AMERICAN ACADEMY 



of Wallach had been proved beyond all doubt to be different from 

 that which Bennett and I had described by a comparison of the crys- 

 talline form of the two acids, and it would follow then that Wallach's 

 acid could not have the formula he assigned to it. The formation of 

 an acid with different structure from chloralid could, however, be 

 explained upon the assumption that the chlorpropiolic acid was the 

 first product of the reduction, and that this passed, on the one hand 

 by the addition of hydrogen, into the |3 chloracrylic acid, and on the 

 other hand formed dichloracrylic acid by addition in the subsequent 

 treatment with strong hydrochloric acid which Wallach prescribes.* 

 Although this hypothesis was far from satisfactory, it seemed to me 

 hardly more improbable than that a similar molecular rearrangement 

 had taken place in the reaction which had come under my own obser- 

 vation. 



Still another difficulty was to be found in the formation of the 

 dibromacrylic acid in question from the tribrompropionic acid melting 

 at 92°, which, if the ordinarily accepted formula for the latter, — 



CH^Br 



CBr^ 

 I 

 COOH 



were correct, would prove the incorrectness of the formula assumed. 

 I was at first unable to attach any great importance to this argument, 

 inasmuch as the constitution of the monobromacrylic acids was ex- 

 tremely uncertain. For although the discovery by Wallach of the 

 B monobromacrylic acid melting at 115° had rendered the coustitution 

 of the a and ^ monobromacrylic acids of Tollens extremely doubtful, 

 it by no means proved their identity. 



Ei'lenmeyer has, however, recently shownf that the a and ^ acids of 

 Tollens, as well as their potassium salts, crystallize in identical forms, 

 and the structure of the tribrompropionic acid melting at 92° is there- 

 fore put upon quite another footing. Since the same (a) monobrom- 

 acrylic acids can be made from a dibromjiropionic and also from its 

 isomer, the a /3 dibrompropionic, it follows that this acid must have the 

 structure, — 



* Ann. Chem. u. Pharm., xcxiii. 7. 



1 Berichte der deutscb. chem. Gosellsch., xiv. 1867. 



