Polyhalogenated ethanes

The reductive dehalogenation of polyhalogenated methanes (Castro et al. 1985) and polyhalogenated ethanes (Li and Wackett 1993) by Pseudomonas putida strain PpG786. 

Names of characteristic groups always cited as prefixes. The names of the two polyhalogenated ethanes, a and b, are a good illustration of the application of the rule of lowest locants and of the alphabetical order to assign lowest locants. 

From the reaction products of the polyhalogenated ethanes and propanes shown in Table 13.7 we deduce that such halogenated compounds may react in aqueous solution by yet another type of reaction, so-called /3-elimination. In this reaction, in addition to the leaving group (L ), a proton is lost from an adjacent carbon atom (hence the prefix /3-) and a double bond is formed ... 

In this, as in many other cases in aqueous solution, OH" plays the role of the base. Note that for compounds such as 1,1,2,2-tetrachloroethane and pentachloroethane, the base catalyzed reaction is important at quite low pH values (/NB = 4.5, i.e., pH at which the neutral and base catalyzed reaction are equally important, see Table 13.7 and Section 13.3). In fact, for polyhalogenated alkanes a small7NB value (e.g., <7) is indicative of an E2 reaction, or, in special cases, of an E1CB reaction see below. Some other examples of compounds reacting by an E2-mechanism include 1,1,2-trichloro-ethane, 1,1,2-tribromoethane, and l,2-dibromo-3-chloroethane (see Table 13.7). A high /NB value (e.g., >10) does not, however, necessarily exclude ( elimination, because this reaction may also occur with water as base, or by an alternative to the SN1 mechanism (i.e., an El mechanism, see below). 

Perlinger, J. A., J. Buschmann, W. Angst, and R. P. Schwarzenbach, Iron porphyrin and mercaptojuglane mediated reduction of polyhalogenated methanes and ethanes in homogeneous aqueous solution , Environ. Sci. Technol., 32, 2431-2437 (1998). 

Analytes CB, chlorobenzenes DDE, l,l-dichloro-2,3-bis(4-chlorophenyl)ethane DDT, l,l-dichloro-2,3-bis(4-chlorophenyl)ethylene DBF, decabromobiphenyls HBCD, Hexabromo-cyclododecane HpBB, heptabromobiphenyl PBB, polybrominated biphenyl PBCCH, pentabromochlorocyclohexane PBDE, polybrominated diphenyl ether PBT, Polybutylene terephthalate PCB, Polychlorinated biphenyl PBDD, polybrominated dibenzo-/ -dioxins PBDF, polybrominated dibenzofuranes PCN, polychlorinated naphthalenes PCP, polychlorinated phenols PBB, polybrominated biphenyl PeBDE, pentabromodiphenyl ether PET, Polyethylene terephthalate PXDDs, polyhalogenated dibenzo-p-dioxins PXDFs, polyhalogenated dibenzofurans TBBPA, tetrabromobisphenol A TBPA, tetrabromophthalic anhydride TCBPA, tetrachlorobisphenol A TDBPP, tris(2,3-dibromopropyl)phosphate. 

Michaelis-Becker reactions between sodium dialkyl phosphites and halogenated alkenes, seem to occur only with polyhalogenated alkenes, but the course of the reaction is then complicated by elimination and addition steps. Thus sodium dialkyl phosphites and 1,1,2-trichlorophenylethene react to give, ultimately, esters of (1-phenyl-1,2,2-ethane)trisphosphonic acid. Such reactions have been reviewed. ... 

Polyhalogenated methanes and ethanes are also reduced in both H2S (1 mM)/ juglone (200 jlM) and the iron porphyrin (2-50 piM) cysteine (5 mM) systems. " The reduction for some alkyl halides in the presence of the iron porphin is indicated by a second-order rate constant, since the rate is proportional to the concentration of both the alkyl halide and the porphyrin (Table 7.9). A half-life at a concentration of 10 pM iron porphyrin is included. 

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