Alkyl halides hydrodehalogenation

Hydrodehalogenation. Unlike slurries of LiAlH4 in ethereal solvents, clear solutions of the hydride in THF reduce alkyl halides to the corresponding alkanes rapidly and often in practically quantitative yield.8 However at least 1 molar equiv. of LiA 1H4 per RX is required (equation I). The rate of reduction for the halides is I > Br>Cl. The effect of the structure on the rate is in the order n-butyl bromide >... 

For efficiency and reasons of economy THF is recommended. Representative dehalogenations in THF are shown in Table 1. Most alkyl halides are reduced at 25 C to alkanes, except for bicyclic halides, such as eA o-2-bromonorbomane. In most cases, the reaction exhibits the typical characteristics of an 5n2 substitution reaction in the reactivity order I > Br > Cl primary > secondary > tertiary. In all cases, no al-kene, or only traces of it, is formed as a side product as a result of elimination. This method provides a convenient synthetic procedure for hydrodehalogenation of alkyl halides. 

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