Poly halogenation

Di- and poly-halogenated aliphatic hydrocarbons. No general procedure can be given for the preparation of derivatives of these compounds. Reliance must be placed upon their physical properties (b.p., density and refractive index) and upon any chemical reactions which they undergo. 

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

Little is known about the tolerance of 1 with unsaturated (poly)halogen compounds. Hydrozirconation of chloroalkenes can lead to competitive cycUzation, and simple reduction of both C=C and C-Cl bonds [98, 222], However addition of 1 to an alkenyl- or propargyl bromide led to the expected product as the sole product of the reaction in excellent yield (Scheme 8-30) [134, 223]. 

Smith, A.G., Francis, J.E., Cabral, J.R.P., Carthew, P., M.M., M. and Stewart, F.P. (1989). Iron-enhancement of the hep-tatic porphyria and cancer induced by environmental poly-halogenated aromatic chemicals. In Free Radicals in the Pathogenesis of Liver Injury (eds. G. Poli, K.H. Cheeseman, M.U. Dianzani and T.F. Slater) pp. 203-216. Peigamon Press, Oxford. 

Schriks, M., Vrabie, C.M., Gutleb, A.C., Faassen, E., Rietjens, I.M.C.M, Murk, A.J. (2006). T-screen to quantify potentiating, antagonistic and thyroid hormone-like activities of poly halogenated aromatic hydrocarbons (PHAHs). Toxicology in vitro, Vol 20, no 4,490-498. 

Although N-halogenated pyrazoles are known, they are quite unstable compounds, increasing in stability from chloro to iodo. They may be implicated in the formation of poly halogenated derivatives (76MI2). There are many examples of competition between nuclear and side-chain halogenation, particularly when radical species can form (90CHE301). 

Alkyl bromides and chlorides. Many simple alkyl bromides and chlorides, and poly-halogenated methanes and ethanes fall into this category, including some common solvents. All should be treated as potentially harmful, but in addition to those already listed above the following may be regarded as some of the more dangerous. 

Participation of Br in marine terpene biosynthesis (Section II.C) is reflected in the impressive number (several hundred) of halogenated terpenes, some with useful biological activities, that have been identified. For example, the poly halogenated sesquiterpenes isoobtusol (14) and isoobtusol acetate (15), isolated from the red alga Laurencia obtussa, showed potent activity against HeLa 229 human carcinoma cells1011. 

In addition, the degradation of Cl and C2 poly halogenated substrates has been reported in non-aqueous (Kotsinaris et al. 1998), aqueous (Horanyi et al. 1982 Liu et al. 2000 Li et al. 2000 Chen et al. 2003) and mixed (Hori et al. 2003 Rondinini et al. 2004 Fiori et al. 2005) solvents, under different operating conditions. The reduction of CH2C12 on Ni and Cu in ACN resulted in the formation not only of methane and chloromethane, but also of ethylene, propene and buthene... 

Bromination proceeds readily with azaindoles to give a monobromo compound, whereas pyrrole and indoles react violently to give poly-halogenated products. 

Porphyrinatoiron(IV) carbenes, including that resulting from the reaction of l,l-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), are produced by reaction of poly-halogenated hydrocarbons with PFe (equation 57) i588,i589... 

Isomerism of Di-chlor Ethanes.—When, however, we study the constitution of the poly-halogen ethanes we find that isomerism occurs just as in the case of the propyl iodides and of the hydrocarbons above propane. In the case of ethane it is a fact that only one mono-substitution product of any type is known, thereby proving the symmetry of the ethane molecule and the like character of all six of the hydrogen atoms. When two hydrogen atoms are substituted by two chlorine atoms two dif event compounds are produced both having the composition C2H4CI2. From the constitution of the ethane molecule, that has been established by its synthesis from methane (p. 16), we can readily see how this may be explained as we may have two hydrogen atoms replaced by two chlorine atoms in two different ways, as follows ... 

The next group of poly-substitution products are those containing two or more cyanogen radicalsy (—CN). These correspond exactly to the poly-halogen compounds, from which they may be prepared by the action of potassium cyanide. 

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