The reaction mechanism for the industrial Wacker process (olefin oxidation via palladium(II) chloride) has received significant attention for several decades.  Aspects of the mechanism are still debated.  A modern formulation is described below:
The initial stoichiometric reaction was first reported by Phillips. The net reaction can also be described as follows:
:[PdCl] + CH + HO → CHCHO + Pd + 2 HCl + 2 Cl
This conversion is followed by reactions that regenerate the Pd(II) catalyst:
: Pd + 2 CuCl + 2 Cl  → [PdCl] + 2 CuCl
: 2 CuCl +  O + 2 HCl → 2 CuCl + HO
Only the alkene and oxygen are consumed. Without copper(II) chloride as an oxidizing agent, Pd(0) metal (resulting from beta-hydride elimination of Pd(II) in the final step) would precipitate, stopping the reaction after one cycle. This stoichiometric reaction was discovered in 1894. Air, pure oxygen, or a number of other reagents can then oxidise the resultant CuCl-chloride mixture back to CuCl, allowing the cycle to continue.