The electrochemical oxidation of mercury (II) - Olefin complexes

Abstract

It has been known for many years that acidic solutions of mercuric ions absorb olefins rapidly to form o bonded complexes. The electro-chemical oxidation of eleven such complexes (those of ethylene, propena, but-1-ane, but-2-ene, pent-l-ene, pent-2-ene, hex-l-ena, hex-2-ene, oct-1-ene, isobutane and cyclohexene) is reported. The high solubility of these mercury(II) - olefin complexes allows concentrated aqueous solutions of olefins to be made so that the oxidation can be carried out at high current densities. The electrode reaction is the first reported example of an electrochemical oxidation of a complex resulting in the fission of a metal-carbon bond thus regenerating the mercuric ion. The mercuric ion can, therefore, be regarded as a catalyst since the complex may be readily regenerated by bubbling olefin through the solution. The effect of pH (for the propene complex) and of electrode potential (for the propene, but-1-ene and but-2-ene complexes) on the products of the reaction was investigated. The products of the oxidation of the complexes of eleven olefins were determined at one fixed potential. The principal products which are found are carboxylic acids, together with small amounts of aldehydes and ketones which, it is shown, are probably the first products of the electrode reaction. A mechanism which involves the rearrangement of a carbonium ion has been suggested for the reaction. The carbonium ion can rearrange either by an alkyl or a hydride shift and the ratio of products formed via these two routes has been shown to depend on the size of the migrating group and, for propene, on the anion present. Values of the ratio of alkyl to hydride shift were obtained for several alkyl groups and the relative alkyl to alkyl shift ratios calculated from these are compared with values in the literature.

More information

Identifiers

Catalogue record

Export record