Polyhalogenated compounds dehalogenation

Nastainczyk W, Ahr H, Ulrich V, et al. 1982a. The mechanism of the reductive dehalogenation of polyhalogenated compounds by microsomal cytochrome P450. 799-808. 

Certain metal carbonyls are very useful for the removal of halogens from polyhalogenated compounds. In these reactions, again, an oxidative addition step should be important. As shown below, carbenes 33>, cyclobutadiene 34>, and benzyne complexes 35> are formed by the dehalogenation reaction with metal carbonyls. 

The mechanism of reductive dehalogenation of polyhalogenated compounds by microsomal cytochrome P450 has been studied in detail [22]. The main products of the in vitro metabolism of hexa- and pentachloroethane were tetra- and trichloroethene, respectively. In this case, the reductive dehalogenation probably proceeds by two sequential one electron reductions forming first a radical and then a carbanion. The carbanion may undergo... 

Tri- -butyltin hydride shows substantial selectivity toward polyhalogenated compounds, permitting partial dehalogenation. The reason for the greater reactivity of... 

The influence of electron density distiibution in the radical-anioa on the rate of carbon-halogen bond cleavage was discussed on page 94. This effect makes possible the selective dehalogenation of polyhalogen aromatic compounds. Examples... 

In the following we will try to illustrate these general points by discussing two specific types of redox reactions the reduction of aromatic nitro groups (Eq. 14-9) and the reductive dehalogenation of polyhalogenated Cr and C2-compounds (Eqs. 14-6 to 14-8). These two cases represent two very different types of reactions. In the first case, the transfer of the first electron is reversible, whereas in the second case, it is typically irreversible and involves the breaking of a bond. In the latter case, therefore, one speaks of a dissociative electron transfer. Furthermore, compounds... 

Silver electrodes have been employed in form of an expanded silver sheet on a plastic plate in the dehalogenation of polyhalogenated heterocyclic compounds examples are given in Chapter 18. 

The dehalogenation of aryl halides was efficiently performed in refluxing THF using a catalytic combination composed of Ni /IMes/i-PrONa. IMes was the most effective NHC, compared to IPr, SIPr, SIMes, ITol, SITol, or ItBu, for the dehalogenation of functionalized aryl chlorides, bromides, iodides and polyhalogenated (hetero)aromatic compounds [eqn (10.2)]. 

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