Halogenation, of unsaturated

Winterton, N. Seddon, K. R. Patell, Y. Halogenation of unsaturated hydrocarbons in ionic liquids, World Patent WO 0037400 (2000). 

Halogenation of unsaturated hydrocarbons involves addition of halogen atoms. For example,... 

Beres et al. (1957) have described the preparation of I -triolein as follows I -monochloride has been added to one of the double bonds in the fatty acid part of glyceryl trioleate. This material is a clear, colorless oil liquid at room temperatiure. Repeated assays have shown that 98 to 100% of the P is bound to the neutral fat. However, thin-layer chromatography has revealed that P and P can react to a greater extent widi minor lipid contaminants than with the triolein itself (Tuna et al., 1963 Snyder and Kimble, 1965). Presumably, the iodine and chlorine atoms of ICl add randomly at tihe double bond of oleic acid. The addition of Cl across the double bond of monoolein was recently described by Sink et ail. (1965). The reader is further referred to a detailed review by Sonntag (1961) for a discussion of reaction mechanisms involved in the halogenation of unsaturated lipids. 

Olefin and acetylene complexes of Au(I) can be prepared by direct iateraction of the unsaturated compounds with a Au(I) hahde (190,191). The resulting products, however, are not very stable and decompose at low temperatures. Reaction with Au(III) hahdes leads to halogenation of the unsaturated compound and formation of Au(I) complexes or polynuclear complexes with gold ia mixed oxidatioa states. 

The determination of iodine value (IV), AOCS Tg 1-64, is sometimes used to determine the extent of unsaturation. Because the tertiary aUyflc hydrogen ia the compounds is capable of substitution by halogen atoms, this only approximates a value for the degree of unsaturation. 

Halogenated Butyl Rubber. Halogenation at the isoprene site ia butyl mbber proceeds by a halonium ion mechanism leading to a double-bond shift and formation of an exomethylene alkyl haUde. Both chlorinated and brominated mbber show the predominate stmcture (1) (>80%), by nmr, as described eadier (33,34). Halogenation of the unsaturation has no apparent effect on the isobutylene backbone chains. Cross-linked samples do not crystallize on extension due to the chain irregularities introduced by the halogenated isoprene units. 

The composition of an oil and the progress of its hydrogenation is expressed in terms of its iodine value (IV). Edible oils are mixtures of unsaturated compounds with molecular weights in the vicinity of 300. The IV is a measure of this unsaturation. It is found by a standardized procedure. A solution of ICl in a mixture of acetic acid and carbon tetrachloride is mixed in with the oil and allowed to reac t to completion, usually for less than I h. Halogen addition takes place at the double bond, after which the amount of unreacted iodine is determined by analysis. The reaction is... 

Forms of BR and polyisobutylene. The properties of butyl rubber and polyisobutylene depend on their moleeular weight, degree of unsaturation, nature of the stabilizer incorporated during manufacture and, in some cases, chemical modification. It is common to produce halogenated forms of butyl rubber to increase polarity and to provide a reactive site for alternate cure mechanisms [6],... 

Degree of unsaturation. Unsaturation accounts for the existence of carbon-carbon double bonds in resins. It is generally indicated by the bromine or iodine number. Both methods are based on the halogen addition to the double carbon-carbon bonds. Because the different reactivity of bromine and iodine, both numbers cannot be compared. The bromine or iodine number does not necessarily correlate with the reactivity of the resin, for instance in the ageing process. However, within a given resin series of the same structure, relative comparisons can be made. 

The treatment of unsaturated substances with halogen leads to addition to these molecules. This is true not only of bromine and chlorine vapor but also of the less reactive iodine. Substitution also occurs in the presence of light. Examples of such halogenations are listed in Table 12. Figure 32 illustrates the characterization of fluorescein in a bubble bath preparation. Bromination of the fluorescein in the start zone yields eosin. 

The halogenation-dehydrohalogenation of ketones and their derivatives is the most widely applied method for the preparation of unsaturated ketones, and the different combinations of alternatives which exist for both steps extend the scope of this approach. Consequently, this route will be discussed in considerable detail. 

Halogenation of the double bond usually prevents the satisfactory preparation of vinylogous a-halo ketones by direct reaction of unsaturated ketones with... 

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)... 

Halogenation of the 7 position also proves compatible with good antiinflammatory activity. Construction of this compound, aclomethasone dipropionate (80), starts by introduction of the required unsaturation at the 6,7 position by dehydrogenation with DDQ (76). The highly hindered nature of the hydroxyl at position 17 requires that a roundabout scheme be used for formation of the corresponding ester. Thus treatment of 76 with ethyl orthoformate affords first the cyclic orthoformate This then rearranges to the 17 ester on exposure to acetic acid. Acylation of the 21 alcohol is accomplished in straightforward fashion with... 

Sulphonylbenzofurans 638 a-Sulphonyl carbanions 760, 766, 767, 797, 813, 951, 961 acylation of 627-636 addition to unsaturated bonds 636-642 alkylation of 627-636, 781 halogenation of 1058-1060 Michael addition of 642-649 miscellaneous reactions of 653-655 Ramberg-Backlund reaction of 649-653, 1057, 1058... 

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