The Wacker Oxidation Process

The exact catalytic cycle is still under debate [89]. Studies of model compounds provide insight into the mechanism, but these model reactions differ from the actual catalytic cycle, and so may follow a different mechanistic pathway [90-92]. Kinetic studies show that the conversion of ethene follows the rate law in Eq. (3.1). This supports a pre-equilibrium that involves the dissociation of two chloride ions and one proton, thus explaining the sensitivity of the reaction to the presence of chloride ions. 

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Interesting properties may also be obtained when using a mixed addenda system in the presence of a co-catalyst The best known system [34d] is the V-substituted phosphomolybdate in conjunction with Pd for the oxidation of olefins to carbonyl compounds. This is analogous to the Wacker oxidation process based on CUCI2 and Pd. Unlike the Wacker process, the HPA system works at very low chloride concentration, or even in its absence. In addition the HPA is more active and selective and less corrosive. Other examples of such two-component catalytic systems include TF /TP, PT /Pt ", Ru"7Ru ", Br 7Br" and l /h-... 

Oxidation of ethylene to acetaldehyde, the Wacker oxidation process, is one of the most important processes in the current chemical industry. The Wacker oxidation is catalyzed by redox couples of Pd /Pd° and Cu VCu in HCl solutions. This catalytic oxidation Eq. 1 can be decomposed into oxidation of ethylene to acetaldehyde with water at an anode Eq. 2 and reduction of O2 to water at a cathode Eq. 3. 

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