Polychloro compounds

Polybromo compounds (bromoform, s-tetrabromoethane) react similarly at 50°, but simple polychloro compounds (chloroform, carbon tetrachloride and trichloroacetic acid) do not. 

A thiocyanato group can be introduced by treatment of the corresponding chloro or bromo compounds with ammonium, sodium or potassium thiocyanate. In polychloro compounds only one halogen is replaced. 

Evaluating relative reactivity at different positions by competitive displacement in polychloroazines requires the unjustified assumption that the chloro groups have a negligible or equal effect on each other. In a polychloro compound bearing a different kind of substituent, the activation or deactivation of the chloro groups is generally neither equal nor negligible, as already demonstrated. 

Two different approaches have been adopted here in describing fluorination reactions the production of highly fluorinated systems is discussed in this chapter on the basis of a comparison of methods, whereas selective fluorinations are described in Chapter 3 in terms of the conversion of functional groups. If we wish to produce highly fluorinated systems, then the starting materials are usually hydrocarbons, polychloro compounds or, of course, highly fluorinated building-blocks for conversion to other compounds. 

A photochemical route using phase-transfer catalysts for the debromination of dibromostilbene has been reported. The related photodehalogenation of 1,2-dihalides in methanol or triethylamine results in the formation of alkenes.A study of the photochemical behaviour of the polychloro-compound (31) has been reported. ... 

Polychlorinated products may be obtained by further chlorination of chlorine-containing compounds 29, 62, McBee and Hass (55, 55, 56, 59 devised a process for chlorinating an organic compound in such a way that rupture of the carbon-to-carbon bond takes place, and polychloro compounds with fewer carbon atoms than the starting material are obtained. They used the term chlorinolysis to define this process. Further chlorinations of polychloro compounds may lead to the formation of unsaturated compounds. For example, high-temperature chlorination of polychloropentanes and polychlorobutanes, led to production of hexachlorocyclopentadiene 52 and hexachlorobutadiene 60, respectively. 

Bromo- and iodo-heterocycles react rapidly with alkyllithiums, even at temperatnres as low as -100 °C, to give the lithio-heterocycle. Exchange of flnorine is unknown and of chlorine, rare, but is known under special circnmstances, snch as in polychloro compounds. The apparent preparation of a number of lithio-heterocycles by direct reaction of a chloro heterocycle using lithium metal with naphthalene has been reported. Since snch lithiations have to be carried out in the presence of the electrophile, it may be that the process is more complex than it seems. ... 

Mitani M, Kiriyama T, Kuratate T (1994) Addition reaction of polychloro compounds to carbon-carbon multiple bonds catalyzed by semiconductor particles under photoirradiation. 

Of the two isomeric dichlorobenzenes, the more valuable crystalline para compound (mp, 53 C) is formed in the largest quantities, the ratio of para to ortho usually being greater than 2 1. In most technical operations, the chlorination is continued until a peak in monochlorobenzene is obtained. The composition of the charge will vary somewhat, depending on the temperature employed, the catalyst used, and the rate and degree of chlorination, but it will be approximately as follows benzene, 9 per cent monochlorobenzene, 70 pfer cent p-dichlorobenzene, 15 per cent and o-dichloro-benzene, including polychloro compounds, 6 per cent. 

The reactivity of a heteroexcimer has been exploited as a means of degrading low concentrations of chlorinated pollutants such as polychlorinated biphenyls and polychlorinated benzenes. Copolymers of vinylnaphthalene and styrenesulfonic acid form water-soluble, miceUar-hke copolymers with a hydro-phobic core. When the nonpolar chloro-compounds are dissolved in aqueous solutions containing the water-soluble copolymer, they are scavenged into the core, where they undergo photodehalogenation. In these reactions, essentially all the incident radiation is absorbed by the naphthalene chromophores, which form heteroexcimers with the polychloro-compound. The pattern of dechlorination is characteristic of electron transfer rather than direct homolysis. 

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