Halogen addition Chlorine

It IS convenient m equations such as this to represent generic alcohols and alkyl halides as ROH and RX respectively where R stands for an alkyl group In addition to con venience this notation lets us focus more clearly on the functional group transformation that occurs the OH functional group of an alcohol is replaced as a substituent on car bon by a halogen usually chlorine (X = Cl) or bromine (X = Br)... 

The reaction of chlorine and bromine with cycloalkenes illustrates an important stereo chemical feature of halogen addition Anti addition is observed the two bromine atoms of Br2 or the two chlorines of CI2 add to opposite faces of the double bond... 

Table 7. Chlorinated and Mixed Halogen Additive Flame Retardants...

The propylene double bond consists of a (7-bond formed by two ovedapping orbitals, and a 7t-bond formed above and below the plane by the side overlap of two p orbitals. The 7t-bond is responsible for many of the reactions that ate characteristic of alkenes. It serves as a source of electrons for electrophilic reactions such as addition reactions. Simple examples are the addition of hydrogen or a halogen, eg, chlorine ... 

HC1, HBr, and HI add to alkenes by a two-step electrophilic addition mechanism. Initial reaction of the nucleophilic double bond with H+ gives a carbo-cation intermediate, which then reacts with halide ion. Bromine and chlorine add to alkenes via three-membered-ring bromonium ion or chloronium ion intermediates to give addition products having anti stereochemistry. If water is present during the halogen addition reaction, a halohydrin is formed. 

Waters, H. D. C., A. R. Caverhill and P. W. Robertson The Kinetics of Halogen Addition to Unsaturated Compounds, Part XII. Iodine Catalysis of Chlorine and Bromine Addition to Ethyl Cinnamate. J. chem. Soc. (London) 1947, 1168. 

The chlorine adduct to the tetrasubstituted exocyclic double bond in 108 is quantitatively obtained by gas-solid reaction [27]. Conversely, related trisub-stituted double bonds lose HX after the gas-solid halogen addition such as in the reactions of 110 and 112 that give 111 and 113,respectively [28] (Scheme 12). The completion of these solid-state eliminations (Sect. 11) is faster at 100 °C. The product 113 is an interesting substrate for the synthesis of orotic acids. Furthermore, the production of 116 from solid 114 and chlorine gas proceeds with 100% yield via the intermediate adduct 115 [58,60-61] (Scheme 12). 

Michael Faraday reported in 1821 that chlorine addition to alkenes is Stimulated by sunlightand today this is taken to indicate the involvement of a free radical process (equation 26). Free radical chain mechanisms were proposed in 1927 by Berthoud and Beraneck for the isomerization of stilbene catalyzed by Br2 (equation 27), and by Wachholtz for bromine addition to ethyl maleate (equation 28).Later studies showed inhibition of halogen addition by reaction of the intermediate radicals with oxygen, and a free radical chain mechanism for solution and gas phase halogenations as in equation (26) was shown (equation 29). Kinetic and mechanistic... 

The energy density of liquid cathode lithium cells can be further enhanced to over 500 Wh/kg (1000 Wh/dm3) by the use of halogen additives. BrCl, added to lithium-thionyl chloride cells, boosts the OCV to 3.9 V and prevents the formation of sulphur in the early stages of discharge. D-sized cells are manufactured, Addition of chlorine to lithium-sulphur yl chloride cells increases the energy density and improves the temperature-dependent electrical characteristics. 

The ene- pe chlorination, specific with this halogen atom, of alkenes would account for a somewhat different mode of halogen addition, giving usefiil allylic dilorides. Efficient and convenient reagents and methods develtqted are dichlorine monoxide (ChO equation 36), r-butyl hypochlorite, and electro-chemical reactions with chloride ion (equation 37). The ene-type chlorination proceeds smoothly with... 

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