Dibromo-dichloro-methane

PCBs and PCTs are particularly troublesome liquids because of their toxicity and persistence in the environment. They are defined as polychlorinated biphenyls, polychlorinated terphenyls, monomethyl-dibromo-diphenyl methane, monomethyl-dichloro-diphenyl methane or monomethyl-tetrachlorodiphenyl methane. With low electrical conductivity and heat resistance they found wide use as dielectric fluids and were formerly used as hydraulic fluids. PCBs have not been made in the UK since 1977 and whilst most new uses for the substance are banned in most countries, around two-thirds of the 1.5 million tonnes manufactured in Europe and the US prior to 1985 still remain in equipment such as transformers. PCTs have been used in the past in a restricted range of specialist industrial applications. 

Total reduction of unbranched open-chain and cyclic derivatives of dichloro and dibromo alkanes occurs at room temperature within 30 minutes in dichloro-methane solutions containing ca. 2.5 equivalents of triethylsilane and ca. 0.25 equivalents of aluminum chloride.189 The reaction occurs equally well with geminal, vicinal, and m-dihalo alkanes. For example, 1,5-dibromopentane gives n-pen lane in 85% yield when treated in this way (Eq. 53).189... 

Preparation of the Active Polvformals under Phase-transfer Catalysis. The polycondensation of DHTN or DHCH with dibromo- or dichloro-methane was carried out under phase transfer catalysis as shown in equations 2 and 3. Best results were obtained with dibromomethane, 60% aqueous KOH and tetrabutyl ammonium bromide. 

The reagent (2.1 moles) was added at ambient temp, to a soln. of 4-methylphenol in dichloro-methane/mcthanol (5 2) and stirred for Ih until the orange colour disappeared to give 2,6-dibromo-4-mcthylphenol. 

Wang and coworkers have explored and extended the utility of halogenations of indoles by Cu(II)Cl2 and Cu(II)Br2 [50]. The best results were obtained in dichloro-methane or acetonitrile in the presence of NaOH and silica gel. Similar conditions were successfully applied to C-ring substituted 1-methylindoles. When the reaction mixture included water and fefra-butylammonium bromide, the 2,3-dibromo products were formed. 1,3-Dimethylindole gave a good yield of the 2-bromo product under the latter conditions. 1-Unsubstituted indoles often present problems, but by using NaOH/sihca and CuCU, 2-chlorination of 3-methylindole was achieved in 86% yield. 

Bromoform, chloroform, bromodichloro-methane, dibromo-chloro methane Tetrachlorom ethane, chloroform, dichloro-ethane, tetrachloro-ethylene, bromodi-chloro methane, chlorodibromo-methane, bromoform Hexachlorocyclo-pentadiene... 

The azide form of the quaternary ammonium ion exchange resin IR-400 (which exhibits low lfiction-sensitivity) reacts with bromoform, analogously to dichloro-and dibromo-methane, to form the highly explosive triazidomethane. Solutions of above 50% concentration explode in contact with a pipette or on injection into a GLC inlet port. 

Table 11 Unit-cell parameters for dichloro-, dibromo- and di-iodo-methane...

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