The stoichiometric conversion of ethylene to acetaldehyde by an acidic, aqueous solution of PdCl2 was discovered over a century ago,[2] but fifty years passed between the discovery of this reaction and the development of a catalytic method. In 1959, researchers at Wacker Chemie reported that a similar transformation takes place in an aqueous, acidic solution of catalytic PdCl2 and a stoichiometric amount of CuCl2 through which oxygen is bubbled