Halogenated Alkenes

The region of high electron density between the doubly bonded carbon atoms gives alkenes an additional reactivity and in addition to burning and reacting with halogens, alkenes will add on other molecules for example ... 

Perfluorinated organic bromides can be oxidatively fluonnated with elemental fluorine to derivatives containing tn- [124] and pentavalent [/25 126 127] bromine in yields up to 42% Perfluoroheptylbromine tetrafluoride has been used to fluonnate double bonds in halogenated alkenes [127]... 

This type of polyhalo alkane adds to halogenated alkenes in the presence of AICI3 by an electrophilic mechanism. This is called the Prins reaction (not to be confused with the other Prins reaction, 16-53). ... 

Vamvakas S, Dekant W, Berthold K, et al. 1987. Enzymatic transformation of mercapturic acids derived from halogenated alkenes to reactive and mutagenic intermediates. Biochem Pharmacol 36 2741-3748. 

Insertion of the C=C bond into an M-H bond precedes frequently the C-X bond activation in halogenated alkenes. Such a pathway has been suggested for the cobalamin-mediated dechlorinations of cis- and trans-DCE, as well as VC with Ti(III) citrate as a reducing agent [141]. 

Previous derivatization of the extract is necessary to improve the stability of the compounds and the sensitivity and precision of subsequent GC-MS analysis. Silyl derivatives formed for example with MSTFA [43], halogenated alkene derivatives produced with heptafluorobutyric anhydride (HFBA) [36] or pentafluoropropionic acid [58] or anhydride (PFPA), as well as acetate derivatives formed using acetic anhydride [48] have been widely employed. 

Ethanol is both an inducer and substrate of CYP2E1. Indeed, CYP2E1 seems to be structurally geared to favor small volatile molecules such as ketones, aldehydes, alcohols, halogenated alkenes, and alkanes as substrates (36). Moreover, many of these same compounds, like ethanol, are inducers of the enzyme. A major mechanism by which this diverse group of compounds appears to initiate induction is by inhibiting normal enzyme degradation. 

The mechanism for the addition of 50 to anthraquinone (Scheme 52), 1,4-diacetylbenzene (Scheme 53), and 1,2-diacetylbenzene (Scheme 54) has been proposed.326 The addition of 50 to benzophenone followed by reaction with Wilkinson s catalyst formally results in the hydrogenation of a double bond (Equation (262)).325 This species also undergoes stereospecific inertion into the vinyl chloride bond of various halogenated alkenes with high yields in most cases (Equations (263)-(267)).329... 

Several studies have shown that sorption of various organic compounds on solid phases could be depicted as an accumulation at hydrophobic sites at the OM/water interface in a way similar to surface active agents. In addition Hansch s constants [19,199-201], derived from the partition distribution between 1-octanol and water, expressed this behavior better than other parameters. Excellent linear correlations between Koc and Kow were found for a variety of nonpolar organic compounds, including various pesticides, phenols, PCBs, PAHs, and halogenated alkenes and benzenes, and various soils and sediments that were investigated for sorption [19,76,80,199-201]. 

The mechanism for the halogen-alkene addition reaction is a two-step process and is illustrated below using bromine and ethene. 

Henschler D. (1985) Halogenated alkenes and alkynes, in Bioactivation of Foreign Compounds (ed. M.W. Anders), Academic Press, New York, pp. 317—347. 

Treatment of perhalogenated and highly halogenated alkenes with sulfur tetrafluoride in the presence of lead(IV) oxide, which is most likely converted in situ into lead(IV) fluoride, results in addition of fluorine to the C = C bond of the alkenes. The addition proceeds at 100 C to afford per- and polyhalogenated alkanes 5 in yields ranging from a few percent to almost quantitative.190 Representative examples are given. 

Highly halogenated alkenes, e.g. 6, react with sulfur tetrafluoride at elevated temperatures in the presence of Lewis acid type fluorides to afford halofluoroalkanes, which result from both addition of fluorine to the C = C bond and substitution of halogen atoms.191... 

Boron trifluoride has been applied as catalyst in addition of hydrogen fluoride to asymmetrically halogenated alkenes in the liquid phase.52... 

The use of boron trifluoride is particularly advantageous with heavily halogenated alkenes, or with alkenes bearing a trifluoromethyl group which slows down the reactivity of their C = C bond. For more reactive alkenes, boron trifluoride may not be so desirable because it hastens resinification as well as addition the economy of each case should be individually considered. 

Table 2. Addition of Hydrogen Fluoride to Halogenated Alkenes with Aluminum Trifluoride Catalysis...

The hydrobromination of a number of halogenated alkenes has been examined. Allyl bromide reacts with HBr in the absence of peroxides, or upon addition of antioxidants121 or FeCb,61 or in acetic acid,122 to produce primarily 1,2-dibromopropane (equation 74). Allyl chloride behaves similarly.123... 

Stepwise reactions by way of diradical intermediates are also possible they often require rather high temperatures, but they are probably involved in the formation of cyclobutanes by the thermal coupling of alkenes like the halogenated alkene 2.161 with themselves or with dienes like butadiene giving the cyclobutane 2.163. The radical centres in the intermediate 2.162... 

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