12.9 The Reaction of Copper with DMSO/CCl4


Chemical Concept Demostrated: An unusual oxidation reaction of copper metal

Demonstration:

A penny is carefully added to a DMSO and CCl4 solvent mixture, and the beaker is covered with a watch glass.

Observations:

    The copper in the penny, over the course of several days, dissolves in the mixture.  The zinc, meanwhile, remains unaffected.

Explanation:

    The copper metal dissolves to form a colorless solution of CuCl22 DMSO and CO. The proposed mechanism for this reaction proceeds through a CCl2 intermediate, and therefore generates phosgene (COCl2) as another intermediate.

    This reaction is not typical because the copper in the penny is being oxidized, but the zinc in the penny is not.  Generally speaking, zinc is a more reactive element than copper.  Copper is oxidized because of the unusually high stability of the products.