558 J. READ AND M. M. WILLIAMS. 



A NOVEL APPLICATION OP BROMINE WATER IN 

 SYNTHETIC ORGANIC CHEMISTRY. 



By John Read, m.a., Ph.D., and Margaret Mary 

 Williams, b.Sc 



[Read before the Royal Society of N.S. Wales, December 5, 1917.' 



Bromine water is often used as a test for unsaturation in 

 the molecule of organic substances : decolourisation of the 

 reagent being taken to indicate the presence of the ethy- 

 lenic or the acetylenic linkage. In the former case, the 

 reaction has usually been assumed to yield solely a dibromo- 

 compound, in accordance with the subjoined general scheme: 

 RRiO : OR2R3 + Br 2 = RRiCBr*OBrR 2 R 3 . 



We have recently been able to show, however, that in 

 the simplest and best-known case of this kind, namely, 

 that of ethylene, the yield of the dibromide may under 

 suitable conditions fall quite low, the bulk of the product 

 being ethylene bromohydrin. In this instance the bromine 

 water is thus an efficient source, not only of bromine, but 

 also of hypobromous acid, and the two reactions represented 

 below take place concurrently: — 



(1) H 2 C : OH 2 + Br 2 = H 2 OBr * OBrH 2 ; 



(2) H 2 C : OH 2 + HO'Br = H 2 OBr'OH 2 OH. 



Of the total bromine used in a particular experiment, 

 37*5 per cent, was converted to ethylene dibromide, 54*4 

 per cent, was converted to ethylene bromohydrin, and the 

 remaining 8*1 per cent, was eliminated as hydrobromic acid^ 

 formed by a partial decomposition of the hypobromous acid 

 to hydrogen bromide and oxygen. 1 



Prom these figures it is clear that the relative percentage 

 amounts of ethylene converted to dibromide and bromo- 



1 Trans. Chem. Soc, vol. Ill (1917), p. 240. 



