1.2- Dihalides ethylene bromide

Some instances of incomplete debromination of 5,6-dibromo compounds may be due to the presence of 5j5,6a-isomer of wrong stereochemistry for anti-coplanar elimination. The higher temperature afforded by replacing acetone with refluxing cyclohexanone has proved advantageous in some cases. There is evidence that both the zinc and lithium aluminum hydride reductions of vicinal dihalides also proceed faster with diaxial isomers (ref. 266, cf. ref. 215, p. 136, ref. 265). The chromous reduction of vicinal dihalides appears to involve free radical intermediates produced by one electron transfer, and is not stereospecific but favors tra 5-elimination in the case of vic-di-bromides. Chromous ion complexed with ethylene diamine is more reactive than the uncomplexed ion in reduction of -substituted halides and epoxides to olefins. ... 

Preparation of the simplest diamine, ethylene diamine, by ammonolysis of the dihalide is accompanied by the formation of diethylenediamine and triethylenetetramine other methods for its preparation are more suitable. Only the higher homologs of /3-dialkylaminoethyl bromide respond favorably to this treatment. Thus, di-n-butylaminoethyl bromide is converted to the diamine in 55% yield whereas the dimethylaminoethyl bromide undergoes extensive dimerization. Triniethylene bromide reacts with liquid ammonia to form trimethylenediamine (50%) however, experimental details are lacking. When the two halogens in the dihalide approach one another in space as in tetra- and penta-methylene dibromides, then nitrogen spiranes are the main products. ... 

Unexpectedly, the vicinyl dihalides react differently (18). For example, an equimolar mixture of styrene and 1,2-dibromoethane reacts on lithium metal yielding a head-to-head, tail-to-tail polystyrene, ethylene and lithium bromide. Apparently, the adsorbed styrene is reduced and dimerized to the dianions. 

New patent literature dealing with the production of Fluothane (CFa CHBrCl) via reduction of 1,1-dibromo-l-chlorotrifluoroethane with methanolic potash or with isopropanol-u.v. light, the synthesis of the inhalation anaesthetic CHFa CF=CBrCl via dehydrofluorination (soda-lime) of the bromopropane CHFa CFa CHBrCl, the use of fluorocarbon bromides tCFa (CFa) -CFaBr (jf = 4 or 6), Br(CFa) Br (x = 2 or 4), CFa CFBr CFaBr, CeFsBr, or l,2-Br,C,Fa] as contrast media for radio-graphy, and the synthesis of the fluorosilicone —[SiMe(CHa CHa CFa-CFa CCla) 0] — via free-radical addition of the bromide CCla-CFa CFjBr across the double bond in ethylene is now available. Free-radical addition reactions of dihalides of the type X(CF2) X (X = Br or I) are referred to... 

---