Chlorination of alkenes

Another common reaction is the chlorination of alkenes to give 1,2-dihaloalka-nes. Patell et al. reported that the addition of chlorine to ethene in acidic chloroalu-minate(III) ionic liquids gave 1,2-dichloroethane [68]. Under these conditions, the imidazole ring of imidazolium ionic liquid is chlorinated. Initially, the chlorination occurs at the 4- and 5-positions of the imidazole ring, and is followed by much slower chlorination at the 2-position. This does not affect the outcome of the alkene chlorination reaction and it was found that the chlorinated imidazolium ionic liquids are excellent catalysts for the reaction (Scheme 5.1-39). 

Room-temperature ionic liquids may be used as green recyclable alternatives to chlorinated solvents for stereoselective halogenation.577 The bromination of alkenes and alkynes in [bmim][Br] is a/m -stereospecific, whereas that of 1,3-dienes gives selectively the 1,4-addition products. The reactions of arylacetylenes, however, are not selective when carried out in [bmim][PF6]. Tetraethylammonium trichloride, a stable crystalline solid may be used in the chlorination of alkenes and alkynes to afford the products with exclusive anti stereoselectivity.578 It has... 

Some solid-state reactions have been reported for the chlorination of alkenes. For example, styrene upon reaction with a mixture of IOB and hydrogen chloride-treated silica gel gave the dichloro adduct (65%) since no solvent was present, it was essential to use efficient cmshing and grinding [12],... 

Many routes for the chlorination of alkenes exist, and one new entry in recent years has been manganese-based chlorinating reagents. Many of these systems have been prepared by Bellesia and co-workers 410-414). These systems in general produce frans-chlorinated alkenes. In only one system has the proposed halogenating complex been structurally characterized (245). 

Covalent I1" is known also in the compound triphenyliodine, (C6H5)3I, and a large number of diaryliodonium salts, such as (C6H5)2I+X, where X may be one of a number of common anions. Aryl compounds such as C6H5IC12 are also well known and can be prepared by direct interaction they can be regarded as trigonal-bipyramidal with axial chlorine atoms and equatorial phenyl group and lone-pairs. The compounds can be used for chlorination of alkenes. 

Chlorination of alkenes and alkynes. McCann and Brown" have noted that under irradiation tetrachloroethylene reacts with molybdenum(V) chloride to form hexachloroethane and molybdenum(IV) chloride. The yield in this reaction is approximately quantitative. 

Chlorination of Alkenes and Alkynes. The haloamidation of olefins was carried out by reaction of Af-haloimides (X = Cl, Br) with nitriles in the presence of Lewis acids. It was presumed that the reaction involves nucleophilic attack of nitrile on the halonium ion followed by hydrolysis of the products (eq 38). ... 

Chlorination of Alkenes. A novel stereospecific dichlorination of electron rich alkenes has been reported using a manganese reagent generated from Benzyltriethylammonium Chloride and oxalyl chloride (eqs 13-17). No oxygenation b)q)roducts are observed. 

Likewise, the series of fluorous (dichloroiodo)arenes 127-129 and alkyl iodine(III) dichlorides 130-132 (Figure 5.7) have been prepared in 71-98% yields by reactions of the corresponding fluorous iodides with chlorine [69]. These compounds are effective reagents for the chlorination of alkenes (e.g., cyclooctene) and aromatic compounds (e.g., anisole, 4-rcrt-butylphenol and acetophenone). The organic chlorinated products and fluorous iodide co-products are easily separated by organic/fluorous liquid/liquid biphasic workups. The fluorous iodides can be recovered in 90-97% yields and reoxidized with chlorine [69]. 

Normally, the nonnucleophilic solvent carbon tetrachloride (CCI4) is used for the bromination or chlorination of alkenes. But the reaction will also work in pro-tic solvents such as water and simple alcohols. In these reactions, new products appear that incorporate molecules of the solvent (Rg. 10.14). How do the OH or OR groups get into the product molecule To see the answer, write out the mechanism and look for an opportunity to make the new products. The first step... 

This chapter continues our discussion of addition reactions, and many of the mechanistic ideas of Chapter 9 apply. For example, many polar addition reactions start with the formation of the more stable carbocation.The most important new concept in this chapter is the requirement for overall anti addition introduced by three-membered ring intermediates. This concept appears most obviously in the trans bromination and chlorination of alkenes. 

N-Chlorosuccinimide (NCS) chlorination of alkenes has been reported to be catalysed by aryl selenenyl chlorides or diaryl diselenides/ The major products are usually rearranged allylic chlorides, with vinyl chlorides as minor products [e.g. (70) - (71) and (72) in ratio 96 4], although the ratio allylic vinyl chloride... 

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