2.3- Ethylene- 1,2-dihalides

Brown, J. K., and N. Sheppard Infrared spectroscopic studies of rotational isomerism. I. The assignment of the fundamental frequencies of some ethylene dihalides. Trans. Faraday Soc. 48, 128—137 (1952). 

Although catalysis by GSTs is almost always associated with detoxication, a few substrates (e.g., the ethylene dihalides) are bioactivated to more toxic products by this pathway. Recent studies have also... 

Many hundreds of diene polymers were investigated for their suitability as elastomers. Only three of these have achieved widespread commercial acceptance butadiene-styrene copolyipers, butadiene-aciylonitrile copolymers, and poly-2-chlorobutadienes. Other essentially non-diene elastomers such as butyl rubber from isobutene, Thiokol from ethylene dihalides and polysulfides, and silicones have become important for special applications. 

Condensation of an ethylene dihalide with an alkali metal sulfide was studied in the latter part of the nineteenth century. The acid catalyzed polycondensation of certain mercapto alcohols represents a second method of synthesis. 

The use of mixtures of dihalides, Thiokol FA, which has less odour and a lower brittle point than Thiokol A, is produced from a mixture of ethylene dichloride and di-2-chloroethyl formal. 

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. ... 

Bromine and chlorine add rapidly to alkenes to yield 1,2-dihalides, a process called lialogenatioii. For example, approximately 6 million tons per year of 1,2-dichloroethane (ethylene dichloride) are synthesized industrially by addition... 

This type is produced from a mixed dihalide, di-2-chloroethyl formal and ethylene dichloride, and sodium polysulphide. A high molecular weight polymer, ca. 100,000, is produced with predominantly hydroxyl end groups on the polymer chain. The sulphur content of the resultant polymer is 49%. 

A term used to designate the geometric arrangement of moieties attached to two adjacent atoms within a molecule. An example of a vicinal diol would be ethylene glycol (HOCH2CH2OH) and a vicinal dihalide would be 1 -bromo-2-chloroethane. 

Ethylene is also employed as an olefmic component of the Mizoroki-Heck polymerization. Organic dihalides thus couple with ethylene in the presence of a palladium catalyst to afford PAV-type polymers 161 and 162, as shown in Equations (77) and (78). ... 

Addition of X2 (Bt2 and CI2) to alkenes gives vicinaZ-dihalides. This reaction is used as a test for unsaturation (n bonds), because the red colour of the bromine reagent disappears when an alkene or aUcyne is present. For example, when ethylene is treated with Br2 in CCI4 in the dark at room temperatures, the red colour of Br2 disappears rapidly, forming 1,2-dibro-moethane, a colourless product. 

Various organic dihalides are employed in a reaction with sodium polysulfide to produce organic polysulfides (Thiokols). Ethylene dichloride, from the direct chlorination of ethylene, dichloroethyl formal, and /3,0 -dichlorodiethyl ether are the principal dihalides that have been employed in the process (44). These elastomeric polymers have been commercially available for a number of years, and many applications have been developed for them. They have excellent oil resistance and one of their principal uses has been in hose and tank linings in which that property is required. 

SAMPLE SOLUTION (a) Reasoning backward, we recognize 1,1-dichloroethane as the product of addition of two molecules of hydrogen chloride to acetylene. Thus, the synthesis requires converting ethylene to acetylene as a key feature. As described in Section 9.7, this may be accomplished by conversion of ethylene to a vicinal dihalide, followed by double dehydrohalogenation. A suitable synthesis based on this analysis is as shown ... 

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