HILL AND CORNELISON. — CROTONOLACTONES. 15 



steam the substance first carried over contained but little, and the 

 percentage of iodine did not become large until about one half of the 

 material taken had passed over. The material which had thus been 

 partially purified by fractional distillation with steam, could not 

 be further purified by recrystallization, but after boiling for some 

 time with bromine water the iodine compound was oxidized, and 

 a substance was then obtained which after several recrystallizations 

 from alcohol possessed the properties and the composition of pure 

 dibromcrotonolactone. 



0.2439 grm. substance gave 0.3779 grm. Ag Br. 



Calculated for C 4 H,Br 2 2 . Found. 



Brm. 66.12 : 65. 93 



The dibromcrotonolactone can much more readily be made from 

 mucobromic acid by the reduction of its broman hydride. Muco- 

 bromylbromide was described many years ago by Hill and O. R. 

 Jackson,* who made it by the action of phosphoric pentabromide upon 

 mucobromic acid. We have found that phosphorous tribromide is in 

 many respects more advantageous for its preparation. The reaction 

 runs somewhat slowly at 100°, but so smoothly that one molecule of 

 the tribromide is sufficient for three molecules of mucobromic acid, 

 and the yield is about 90 per cent of the theoretical amount. After 

 the reaction is over the flask is well cooled, cold water is added, and 

 the whole vigorously shaken until the oil which first separates solidi- 

 fies in a granular form. The crude product melts at 54—55°, and by 

 repeated recrystallization from small quantities of hot alcohol this 

 melting point may be raised to 56-57°, one degree higher than the 

 point given by Hill and O. R. Jackson. We attempted to purify the 

 crude product by distillation in vacuo, but we found that the melting 

 point was depressed rather than raised by this treatment. We have 

 not further studied the change which is thus apparently brought about 

 by distillation, for we soon found that a perfectly pure dibromcrotono- 

 lactone could be made directly from the mucobromylbromide, as it 

 was precipitated by water, while it was difficult, if not impossible, to 

 do this with the distilled substance of low melting point. Hydriodic 

 acid, or zinc dust with glacial acetic acid, reduces the mucobromyl- 

 bromide to the lactone, although the former reagent yields a product 

 which contains iodine. A far more efficient and convenient reducing 



* These Proceedings, XVI. 174. 



