Reaction Mechanism
The reaction mechanism for the industrial Wacker process (olefin oxidation via palladium(II) chloride) has received significant attention for several decades, and parts of it are still a contentious subject. A modern formulation is described below:
The catalytic cycle can also be described as follows:
- 2 − + C2H4 + H2O → CH3CHO + Pd + 2 HCl + 2 Cl−
- Pd + 2 CuCl2 + 2 Cl − → 2− + 2 CuCl
- 2 CuCl + ½ O2 + 2 HCl → 2 CuCl2 + H2O
Note that all catalysts are regenerated and only the alkene and oxygen are consumed. Without copper(II) chloride as an oxidizing agent Pd(0) metal (resulting from reductive elimination of Pd(II) in the final step) would precipitate out and the reaction would come to a halt (the stoichiometric reaction without catalyst regeneration was discovered in 1894). Air, pure oxygen, or a number of other oxidizers can then oxidise the resultant CuCl back to CuCl2, allowing the cycle to repeat.
The initial stoichiometric reaction was first reported by Phillips and the Wacker reaction was first reported by Smidt et al.
Read more about this topic: Wacker Process
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