Olefins elemental halogens

Insertion Reactions into Element-Halogen Bonds 11.6.2. Insertions of Acetylenes and Olefins... 

What is the structure of the alkyl halide that will undergo dehydrohalogcnation and yield Il-a as the major product Answer The olefin is formed by removing the elements of HX from two adjacent carbon atoms (olefmic carbon atoms in product). Thus, we merely have to add the elements of HX to the desired product to find the structure of the required alkyl halide. This can be accomplished in the two ways A and B shown below. We shall use Br as the halogen, although Cl and I will also work. 

Halohydrins are /I-halogenated alcohols. They can be obtained in H20-containing solvents from olefins and reagents, which transfer Hal+ ions. TV-Bromosuccinimide (transfers Br+ Figures 3.33 and 3.34 as well as 3.36), chloramine-T (transfers Cl+ Figure 3.35), and elemental iodine (transfers I+ Figure 3.36) have this ability. Bromonium and chloronium ions are then attacked by H20 according to an SN2 mechanism. This furnishes the protonated bromo- or chlorohydrins, which are subsequently deprotonated. 

The chemical reactivity of organometallic compounds, in particular those of the elements of Groups I, II, and III, renders them well-suited to study by reaction calorimetric methods. Examples reported include measurements of the heats of hydrolysis of alkyls of Li, Zn, Cd, and Al, the heats of hydroboration of olefins, and the heats of halogenation of alkyls of Zn, Cd, Hg, Sn, and Ga. The heat of formation data derived by use of these methods are discussed in the following Section, in which best AHf° values are selected from the available published data on compounds containing metal-carbon bonds. 

Halogenation— This reaction incorporates one of the halogen elements, usually chlorine or fluorine into a compound. Halogen gas can be used, as in the addition of chlorine to benzene to form chlorobenzene. Copper chloride on various supports are also used to add CI2 or HC to olefins. Fluorine or HF can be added to olefins. 

Halogenated butyl rubbers are made by reacting elemental bromine or chlorine with butyl rubber dissolved in a light (C5-Cg) aliphatic hydrocarbon such as hexane. The olefinic unsaturation remains, but the double bonds move from the backbone to adjacent pendant positions, and the halogen attaches itself to the carbon atom which is allylic to the double bonds (Fig. 6). Commercial halobutyls contain, typically, 1-1-1-3 wt % of chlorine or 1 9-21 wt % of bromine. 

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