Chlorinated alkenes

Ensign SA (1996) Aliphatic and chlorinated alkenes and epoxides as inducers of alkene monooxygenase and epoxidase activities in Xanthobacter strain Py2. Appl Environ Microbiol 62 61-66. 

CIS-[Ru(H20)2(dinso) ] is made from as-RuClj(dmso) and Ag(BF ) in aq. EtOH. The system c/s-[Ru(H20)j(dmso) ] Vaq. Na(ClO) or TBHP/CH Cl oxidised alkanes such as adamantane, cyclo-octane, -heptane and -hexane to the corresponding alcohols and ketones as did [Ru(Hj0) PWjj(0)3g ] . A free-radical mechanism may be involved for the TBHP oxidations, but those with (C10) probably involve oxoruthenate(VI) or oxoruthenate(IV) intermediates [823], The oxidative destruction of a-chlorinated alkenes by CM-[Ru(HjO)2(dmso) ] Vaq. Oxone /Me(CH3) jN(HSO ) MCj to carboxylic acids and ultimately to CO and HCl was reported [946],... 

Oxidative destruction of a-chlorinated alkenes by cA-[Ru(H30)3(dmso) ] Vaq. Oxone /Me(CH2)jjN(HSO )Me3 gave carboxylic acids and ultimately CO and HCl forperchoroethylene, trichloroethylene, cA-l,2-dichloroethylene, 1,1-dichloropropene,... 

The addition of hydrogen fluoride to the double bonds of chlorinated alkenes in the presence of an aluminum trifluoride catalyst is effective and has found broad synthetic application (Table 2). It proceeds so effectively that it is sometimes used to remove fluoroalkenes in crude product mixtures by adding hydrogen fluoride in this way.27 28... 

Interest in the bioremediation of chlorinated solvents is widespread. It is impractical to consider all the excellent efforts underway. An example will be given for both a chlorinated alkane and a chlorinated alkene. Both compounds, dichloromethane and trichloroethylene, are commonly used industrial solvents and degreasers that are important soil and water pollutants. 

Ensign, S. A., Hyman, M. R. Arp, D. J. (1992). Cometabolic degradation of chlorinated alkenes by alkene monooxygenase in a propylene-grown Xanthobacter strain. Applied and Environmental Microbiology, 58, 3038-46. 

Alkenes and chlorinated alkenes 10-100 Chlorine content important, AOP support oxidation... 

Two mechanisms of reaction appear possible depending upon the reactants. Initial palladation of other the alkene or the arene may occur alkene palladation is proposed to occur initially in reactions of chlorinated alkenes.2-3 Alkenes without strongly electron-withdrawing chloride substituents and moderately reactive arenes generally react via an initial arene palladation, and the reaction takes the route shown in Scheme l.4... 

Example Reduction of Chlorinated Alkenes by Zero-Valent Iron... 

The chlorinated alkenes are likely to follow one of three basic reaction pathways. 

The kinetics associated with catalytic reactions are complex however, some general trends can be determined. Reactions are often first order with respect to the reactant, and the rates of hydrodechlorination are faster than hydrogenation. Polyaromatic compounds react faster than monoaromatic compounds, and chlorinated alkenes react faster than their corresponding alkanes. Finally, the reaction rate often increases with increasing degree of chlorination, though this does not hold true for the chlorinated ethylenes. 

Sensitized addition of cyclic dienes with chlorinated alkenes, employing an excess of the latter, yields mixtures of [4+2] and [2+2] adducts (Sch. 10). A substantial proportion of [4+2] adduct 46a is formed when cyclopentadiene 32 is the diene, but cyclohexadiene 36 yields almost entirely the [2+2] adduct 46b. Use of acyclic 1,3-dienes leads only to [2+2] products. The regioselectivity of the cycloadditions is consistent with a biradical intermediate 48 [47]. Sensitized irradiation of cyclopentadiene with 1-acetoxy acrylonitrile 49 also gives a [4+2] and [2+2] mixture, but with a higher proportion of the [4+2] adduct than the reactions using chloro-alkenes 45 [33-35]. 

Chlorination.1 In combination with A1C13, this reagent chlorinates alkenes to provide vinyl chlorides and chlorinates arenes, but not benzene, to provide aryl chlorides. Anisole, diphenyl ether, and N,N-dimethylaniline are chlorinated exclusively in the para-position. Bromination can be effected by the combination of 1 with aluminum bromide. 

Chlorinated alkenes are similar to chlorinated alkanes. The two chlorinated solvents most frequently found in groundwater are trichloroethene and tetrachloroethene. Although not used as a solvent, 1,2-dichloroethene may be found due to the breakdown of other alkenes, Vinyl chloride may occur as a breakdown product of other chlorinated alkenes, but is most likely to be found in water as a consequence of the leaching from polyvinyl chloride (PVC) water pipes, which contain high residuals of vinyl chloride. This chemical is usually best controlled through product specifications. 

SbCls also chlorinates alkenes and is reduced to the much less reactive SbCl3. This reaction probably prevents formation of high molecular weight polystyrenes [145]. 

Chlorination. Alkenes form dichlorides under oxidative conditions (MnClj-LiOMe-Oj HCl). Lithium 4-pentenoates give y-lactones. 

In Xanthobacter sp. strain Py2 both the alkene monooxygenase and the epoxidase are induced by C2, C3, and C4 alkenes, and also by chlorinated alkenes including vinyl chloride, cis- and trans-dichlo-roethene and 1,3-dichloropropene (Ensign 1996). 

From an environmental point of view, it therefore appears that the complete degradation of chlorinated alkenes and alkanes will often require the operation of both anaerobic and aerobic steps for example, partial or complete dehalogenation may occur under anaerobic conditions, and aerobic degradation of the partially dechlorinated metabolites such as dichlo-romethane (La Roche and Leisinger 1991) and vinyl chloride (Castro et al. 1992a,b Hartmans and de Bont 1992) may then subsequently take place. The combination of the two activities in a single strain has been exploited in the genetically constructed strain of P. putida and has been discussed above. 

Fig. 27 Kharasch addition to chlorinated alkenes vinylchloride, vinylidenedichloride, allylchlo-ride and 2-chloropropene [29, 33-35]...

Many routes for the chlorination of alkenes exist, and one new entry in recent years has been manganese-based chlorinating reagents. Many of these systems have been prepared by Bellesia and co-workers 410-414). These systems in general produce frans-chlorinated alkenes. In only one system has the proposed halogenating complex been structurally characterized (245). 

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