Reductive dehalogenation, reaction

Totten LA, U Jans, AL Roberts (2001) Alkyl bromides as mechanistic probes of reductive dehalogenation reactions of vicinal stereoisomers with zerovalent metals. Environ Sci Technol 35 2268-2274. 

As pointed out earlier a third class of B12-dependent enzymes, present in anaerobic microbes, carry out reductive dehalogenation reactions, which play an important role in the detoxification of chlorinated aliphatic and aromatic compounds, among which are many important man-made pollutants. The role of B12 in this class of enzymes is not clear— possibly by formation of an organocobalt adduct, as in the case of methyltransferases or alternatively by the corrinoid serving as an electron donor. 

As indicated in Chapter 8, the production of alkanes, as by-products, frequently accompanies the two-phase metal carbonyl promoted carbonylation of haloalkanes. In the case of the cobalt carbonyl mediated reactions, it has been assumed that both the reductive dehalogenation reactions and the carbonylation reactions proceed via a common initial nucleophilic substitution reaction and that a base-catalysed anionic (or radical) cleavage of the metal-alkyl bond is in competition with the carbonylation step [l]. Although such a mechanism is not entirely satisfactory, there is no evidence for any other intermediate metal carbonyl species. 

Reductive dehalogenation reactions catalyzed by P-450 have been studied extensively, primarily because of the interest in compounds such as anesthetics, pesticides, and potentially toxic industrial solvents. An anesthetic named halothane gives anion-radical that undergoes dehalogenation according to the following equation ... 

Consequently, with the present knowledge of reductive dehalogenation reactions of Cr and C2-compounds, and considering the quality of the various molecular descriptors, only qualitative, or at most semiquantitative, predictions of the relative reactivities of a confined set of structurally related compounds in a given system are possible. Nevertheless, evaluation of such relative reactivities in different systems may provide important insights into such reactions, which will be demonstrated by the following two examples. These two examples will, however, also illustrate the... 

Why is it so difficult to derive generally applicable quantitative structure-reactivity relationships (QSARs) for redox reactions involving organic compounds What is particularly problematic when dealing with reductive dehalogenation reactions ... 

For permeable reactive barriers, the monitoring effort must consider the contaminant that exceeds the groundwater standards. In addition, monitoring of degradation products from reductive dehalogenation reactions or other contaminant transformation products may be required. Other groundwater parameters such as pH, alkalinity, specific conductance, and major compositions with respect to cations and anions must be included... 

Reductive Dehalogenation Reactions of Halogenated Aliphatic and Alicyclic Compounds... 

Narayanam JMR, Tucker JW, Stephenson CRJ (2009) Electron-transfer photoredox catalysis development of a tin-free reductive dehalogenation reaction. J Am Chem Soc 131 8756-8757... 

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