Elemental halogens, addition

Additions of elemental halogens to unsaturated compounds are among the most common preparations of halogenated fluoroorganics. The transformations are usually fairly clean and proceed in good yields. Besides the numerous examples of halogen addition tofluoroalkenes and fluoroalkyl-substituted alkenes, additions to perfliioropropyl vinyl ether [2] and fluormated styrenes [7, 4] have been reported. Both ionic and free-radical processes occur (equations 1 and 2)... 

Conjugated, cross-conjugated, and homoconjugated fluoroalkenes react with halogens to yield predominantly 1,4-adducts Results from the reactions of a series of conjugated fluoroalkenes with elemental halogens are summarized in Table 4 In nearly all cases, the fraMs-l,4-addition products are formed exclusively [Il ... 

Like simple elemental halogens, iodine monochloride reacts with conjugated fluorodienes to yield mostly 1,4-addition products. These bidirectional reactions lead to mixtures of regioisomers, as shown in Table 5 [//]. 

Now that we ve covered the chemistry of hydrocarbons, it s time to start looking at more complex substances that contain elements in addition to C and H. We ll begin by discussing the chemistry of organohalides, compounds that contain one or more halogen atoms. 

Note Such halogenation can be done by addition of elemental halogen to alkenyl or alkynyl groups or by replacement of one or more of the hydrogen atoms attached to alkyl or aryl substituents, using a variety of reagents. 

For the cobalt(III) complexes this method offers the additional advantage of rapid, controlled oxidation of the cobalt(II) intermediate complex to the cobalt(III) complex through the direct use of the elemental halogen corresponding to the anion of the desired salt, which eliminates the long air oxidation and the possible undesirable side reactions. 

The heterocyclic tellurium compounds can also be isolated from the reaction mixtures by extraction with dichloromethane and distillation3 or by precipitation of the telluracyclohcxane dihalides upon addition of elemental halogens to the extracts4. 

Diorgano tellurium compounds are easily oxidized by elemental halogens to diorgano tellurium dihalides. Generally, the reactions are carried out with solutions of the reagents in inert organic solvents such as diethyl ether, methanol, acetonitrile, dichloromethane, chloroform, carbon tetrachloride, fluorotrichloromethane, benzene, or toluene. Often, the diorgano tellurium dihalides precipitate quantitatively from the reaction mixture. Soluble products are isolated by evaporation of the solvent or by addition of petroleum ether or hexane. 

The addition of elemental halogen or hydrogen halides to C-C multiple bonds is the most important halogenation reaction in industrial chemistry. At present, 1,2-dichloroethane (DCE, by chlorination of ethylene) is among those chemicals with the highest production rates and is now used as a starting material for the production of poly (vinyl chloride) (PVC, Scheme 2) [6], Vinyl chloride monomer (VCM) can be achieved by three different routes. 

A number of inorganic species also absorb. We have noted that many ions of the transition metals are colored in solution and can thus be determined by spectrophotometric measurement. In addition, a number of other species show characteristic absorption peaks, including nitrite, nitrate, and chromate ions, the oxides of nitrogen, the elemental halogens, and ozone. 

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