β-elimination in the reactions of ·CR¹R ²CR³R⁴X radicals with metal powders immersed in aqueous solutions

The reactions of several radicals of the type ·CR¹R ²CR³R⁴X (where X = OH or NH₃ ⁺) with metal powders that have been immersed in aqueous solutions were studied. The radicals were formed by radiation chemical techniques. One of the products in all these reactions is the corresponding alkene, R ¹R²C=CR³R⁴. The results are in accord with a mechanism in which the radicals react with the metals that are forming transients with metal-carbon σ bonds. The latter transients decompose via two competing reactions: (a) heterolysis of the metal-carbon σ bond and (b) β-elimination of X^-. Moreover, the dehalogenation of BrCH₂CH₂NH₃⁺ and ClCH₂(CH₃)₂COH by metal powders was studied. Also in these reactions, the corresponding alkene is one of the products. This result is consistent with the suggestion that, in the dehalogenation reaction, an alkyl radical is formed in the first step. This radical then reacts with the metal. Alternatively, the transients with metal-carbon σ bonds in the dehalogenation processes might be formed via a concerted mechanism.