Chloroethylene reaction

In the gas phase addition of Cl atoms to chloroethylenes, reaction-35, requires... 

Oxidative reactions of dienes are accomphshed under similar conditions as those of alkenes. Abicydic diene synthesized from hexafluorobenzene and 1,2-di-chloroethylene is monoepoxidized by triflnoroperoxyacetic acid [43] (equation 35). 

Tlie reaction of l,l-bis(dialkylamino)-2-chloroethylenes 50 with elemental sulfur in the presence of EtsN yielded the corresponding inner salts 51 in high yields. It was assumed that the elimination of HCl from the dithiirane intermediates 52 formed the inner salts 51 [92JCS(CC)1522 97HAC505]. 

The rates of radical-monomer reactions are also dependent on considerations of steric hindrance. This is easily observed by considering the reactivities of di, tri-, and tetrasubstituted ethylenes in copolymerization. Table 6-5 shows the kn values for the reactions of various chloroethylenes with vinyl acetate, styrene, and acrylonitrile radicals. The effect of a second substituent on monomer reactivity is approximately additive when both substituents are in the 1- or a-position. However, a second substituent when in the 2- or (3-position of the monomer results in a decrease in reactivity due to steric hindrance between it and the radical to which it is adding. Thus 2-10-fold increases and 2-20-fold decreases in the reactivities of vinylidene chloride and 1,2-dichloroethylene, respectively, are observed compared to vinyl chloride. 

Niki, H., Maker, P. D., Savage, C. M., Breitenbach, L. P., Martinez, R. I. Herron, J.T. (1982). A Fourier transform infrared study of the gas-phase reactions of 03 with chloroethylenes. Journal of Physical Chemistry, 86, 1858-61. 

Addition of chlorine atoms to ethylene and chloroethylenes has been extensively investigated. Some work has also been done on termal chlorination of propylene and butene at higher temperatures. The references and the elementary reactions postulated have been listed by Steacie (97). The mechanism generally assumed is the well known chain chlorination mechanism. When the initiation is photochemical, this comprises the following reactions... 

A similar electrophile, iodosyl triflate, CF3S020I0, was employed with arylsi-lanes [98]. The same reagent upon reaction with Me3SiCN formed (CN)2I+ TfO" which was coupled with tributyltin substituted arenes or heterocycles to afford bis(heteroaryl)iodonium triflates, e.g. dithienyl and difuryl derivatives [99]. However, this method gave poor results with nitrogen heterocycles. For them another approach was developed based on the reaction of the appropriate lithium compound with / -(dichloroiodo)chloroethylene (Scheme 33). Pyridine and quinoline compounds were formed in this way in moderate yield (23-71 %) [100]. 

The requirement for a positive j8-carbon is also reflected in Table 8, which summarizes the known Hammett p values. All these are positive, with the least reactive system showing the highest response to substituent change. The p value for the diarylhaloethylene-ethoxide ion reaction is the highest, followed by that for the reaction with the more reactive p-toluenethiolate ion. In the a-arylsulphonyl-/J-chloroethylene series, the highest values are again for the slow azide reaction, but... 

The reactivity order of the a-aroyl-j3-chloroethylene-ethoxide ion reaction does not follow the Hammett equation (Kudryavtseva et al., 1963), since the activating order of p-substituents isp-Cl>H>p-Br> p-Me. The anomalous position of the p-Br derivative, which should be more reactive than the unsubstituted one, was ascribed to the operation of the + M effect of the bromine atom, which is stronger than its usual —I effect. 

The reactivity of the halide ions could not be evaluated directly since they have not been studied with the same substrate. However, -toluene-thiolate ion is nine orders of magnitude more reactive than chloride ion towards 2-chloro-l,l-diarylethylenes in dimethylformamide. Although comparison may not be justified (see below), a similar reactivity ratio exists for the reactions of j8-bromo-j -nitrostyrene with iodide ion in butyl cellosolve and thiophenoxide ion in methanol. Bromide ion is 0-6 times as reactive as chloride ion towards l-anisyl-l-phenyl-2-chloroethylene. These relative reactivities of the halide ions should be regarded only as rough estimates. Their very low reactivity is also shown by the chloride exchange in ethyl /3-chlorocrotonate, which is at least 106 times slower than the substitution by thioethoxide ion (Jones et al., 1960) while trichloroethylene does not exchange at all even at 245° (Bantysh et al., 1962). 

For example, 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA) is transformed into 1,1-di-chloroethylene by dihaloelimination [28]. Butler and Hayes [28] tabulate pseudo-first-order reaction rates for dihaloelimination of TeCA, HCA, penta-chlorethane (PCA),and 1,1,2-TCA. 

Similar conclusions are drawn by Cvetanovic et al. from their results of ozonization of alkenes in the gas phase (9) and in CC14 solution (10). The rate constants for the ozonolysis of chloroethylenes and allyl chloride, in CC14 solution, indicate (11) that the rate of ozone attack decreases rapidly as the number of chlorine atoms in the olefin molecules is increased. However, to explain the departures from simple correlations, in some cases steric effects and the dipolar character of ozone had to be invoked (10). The relevance of the dipolar character of ozone in its reactions has also been stressed by Huisgen (12), who provided evidence that the ozone—olefin reaction is usually a 1,3-dipolar cycloaddition. 

Diynes. A general method for preparation of 1,3-diynes, particularly terminal ones, involves palladium-catalyzed coupling of alkynylzinc derivatives with (E)-l-iodo-2-chloroethylene. This alkene is obtained in 83% yield by reaction of acetylene with iodine monochloride in 6 A HCI. Coupling results in a l -chloro-1,3-cnync (1), which is converted into a l-sodio-l,3-diyne (2), which in turn can be reduced or alkylated to give a 1,3-diyne. 

Norbornadiene (Problem 14.38) can be prepared by reaction of chloroethylene with cyclopentadiene, followed by treatment of the product with sodium ethoxide. Write out the overall scheme, and identify the two kinds of reactions. 

Liu, L., Davis, S. R. Ab initio study of the Grignard reaction between magnesium atoms and fluoroethylene and chloroethylene. J. Phys. Chem. 1991, 95, 8619-8625. 

A mechanism analogous to equation 14 has been observed with respect to OH reactions with halouracils" " and nitrouracils" , nitro- and bromofurans and chloroethylenes, e.g. in the case of uracil (equation 16). 

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