Ethylene halides

The ethylene halides may be prepared by direct halogenation of ethane, but this is not a practical method as it yields a mixture of the two isomeric compounds as in the further halogenation of the monohalogen ethanes. The best method of preparation is from the unsaturated hydrocarbon, ethylene. This reaction has been fully considered already (p. 154) and need not be discussed again. 

The most important reactions of the ethylene halides are those in a series that takes place with the loss of hydrogen-halide. The hydrogen and the halogen are lost from different carbon groups, with the conversion of the saturated di-halide into an unsaturated mono-halide, as follows  

The unsaturated compound may then take up two halogen atoms, like the ethylene hydrocarbons themselves, going back again to the saturated class of compounds. 

We thus obtain a tri-halogen substitution product of the saturated hydrocarbon. These reactions may be repeated, yielding, each time, a halogen product of the saturated hydrocarbon containing one more halogen atom. We may thus pass from di-halogen ethane to hexa-halogen ethane. The entire series of reactions is as follows  

One more reaction of the ethylene halides must be mentioned, as, in it, we have a direct proof that the structure of ethane is as represented, viz., the symmetrical structure. Our evidence of this structure, thus far is simply indirect, i.e., from the proof that the other isomeric di-halogen ethane has the unsymmetrical structure. 

---

The p-naphthyl ethers of methylene halides have m.p. 133°, of ethylene halides 217°, and trimethylene halides 148°. 

The 2-naphthyl ethers from methylene halides have m.p. 133 °C, from ethylene halides 217 °C and trimethylene halides 148 °C. 

Hine, J. Brader, W. H. The effect of halogen atoms on the reactivity of other halogen atoms in the same molecule. III. The Sn2 reactivity of ethylene halides./. Am. Chem. Soc. 1953,... 

Another method which has found a little use is exemplified by the alkylation of benzothiadiazine 27a with ethylene halides to give the thiadiazolo-thiadiazine 33 (Scheme 52). When 5 R, the two possible stereoisomers, 33a and 33b, are obtained (71M1055) (Section II,B,l,c). 

Lourenso " carried out this transformation in the presence of ethylene halides and isolated substances up to = 6 from the reaction medium. He established that the overall structure for compounds of this kind approached that of pure ethylene oxide, although the properties of these substances were different from those of ethylene oxide. Lourengo also noticed that this compound, which was a liquid at room temperature, showed increased viscosity with an increasing degree of polymerizations and he proposed a chain formula for the products. 

---