HILL AND CORNELISON. — CROTONOLACTONES. 3 



treated with bromine in aqueous solution, and the brommaleylbromide, 

 C 4 HBr 3 2 , which, according to the observations of Hill and Sanger,* 

 is thus formed, when carefully reduced by zinc dust and glacial acetic, 

 acid, yielded the body melting at 77°. The nuicobromylbromide 

 C 4 HBr 3 2 described by Hill and 0. R. Jackson f was so simply 

 related, as far as its empirical formula was concerned, to the body 

 C 4 H 2 Br 2 2 formed from tribrompyromucic acid, that it seemed pos- 

 sible to establish experimentally a direct connection between the two. 

 It was found that mucobromylbromide could readily be reduced by a 

 variety of reducing agents, and that under certaiu conditions a nearly 

 quantitative yield of the body C 4 ll 2 Br 2 2 melting at 90-91° could be 

 obtained from it. Moreover, this reaction could be reversed and muco- 

 bromylbromide obtained by the action of bromine upon this reduction 

 product. In the same way, by the reduction of mucochlorylbromide 

 the body C 4 H 2 C1 2 2 melting at 50-51°, which had been made from 

 trichlorpyromucic acid, could readily be obtained in any desired 

 quantity. 



Since the several bodies already mentioned were evidently perfectly 

 similar in their structure, we chose for more detailed study the body 

 C 4 H 2 Br 2 2 , which was the most readily accessible. The melting 

 point of this substance, 90-91°, was not far removed from that assigned 

 (88°) by Toennies t to a body of like formula, which he obtained by 

 the oxidation of ^y-dibrompyromucic acid with bromine water, and it 

 was not difficult to suppose the two bodies identical. Toennies pub- 

 lished no analyses whatsoever of his product, and Hill and Sanger § 

 were unable to obtain the substance in larger quantities; but according 

 to their observations a preparation which gave the proper percentage 

 of bromine melted at 89-90°. A careful comparison of the substance 

 prepared according to Toennies with that obtained by the decomposi- 

 tion of tribrompyromucic acid, or by the reduction of mucobromyl- 

 bromide, showed the two bodies to be identical in every respect. The 

 formation of dibrommaleic acid by the prolonged action of nitric acid 

 upon this body sufficiently established the relative position of the two 

 bromine atoms and left for its constitution the choice between the 

 following formula? : — 



* These Proceedings, XXI. 166. 



t Ibid., XVI. 174. 



t Berichte d. deutsch. chem. Gesellsch., XII. 1202. 



§ These Proceedings, XXI. 172. 



