The Wacker and Monsanto Processes

The previous examples involve reduction (hydrogenation) of organic molecules, but transition metal complexes can also catalyze oxidation. For example, the Wacker process, which has been widely used to convert ethylene to acetaldehyde, depends on catalysis by palladium(II) in the presence of copper(II) in aqueous HCl. The role of the copper chloride is to provide a means of using air to reoxidize the palladium to palladium(II). Once again, Zeise-type coordination of the ethylene to the metal center is believed to be involved  

The Wacker process itself is becoming obsolete, largely because acetaldehyde is now more economically made by the reaction of methanol with CO via oxidative addition to the homogeneous catalyst Rh (CO)2l2 Monsanto process)-. 

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