By adding a copper salt to a gold catalyst, synthetic chemists have eliminated the need for mercury in an important chemical synthetic method.

The reaction of alcohols with alkenes to give ethers is a very useful synthetic method, but has traditionally used highly toxic mercury salts. Chemists at the University of Valencia, Spain, have now found that a more environmentally friendly mixture of gold and copper salts can be used instead.

Gold(III) salts had previously been tried for the reaction of alcohols with alkenes, but tended to get reduced to gold(0) in the reaction mixture, destroying the catalytic activity. Avelino Corma and Xin Zhang found that they could solve this problem by adding copper(II) chloride to the gold(III) chloride catalyst.

The method works because the copper(II) chloride acts as an oxidising agent, slowing down the reduction of gold(III) ions to gold(0). The next stage, said Corma, is to optimise the catalytic conditions, and to extend their method to the additions of alcohols to allenes and alkynes.

The significance of the work was emphasised by A Stephen K Hashmi, an expert in gold catalysis at the University of Heidelberg, Germany, who said that 'the discovery of an increase of the lifetime of a gold catalyst by a copper co-catalyst might well be the basis for industrial applications, and I look forward to future results in this area.'

David Barden