A THEORETICAL-STUDY OF SOME STEPS IN THE WACKER PROCESS

Some crucial steps of the Wacker process have been studied using the recently suggested PCI-80 (parametrized configuration interaction with parameter 80) scheme. These steps include the hydroxyl anion attack on the coordinated olefin and on the palladium atom, the subsequent beta-elimination and vinyl-alcohol insertion steps, and the formation of the final acetaldehyde product. It is found that some of these steps are well modeled by a gas phase complex. This is true for the insertion and elimination steps and for some of the relative energies between stable minima. It is even possible to often remove water ligands without severely affecting the chemistry. Some other steps can not be modeled without an explicit account of the polar solvent. For the hydroxyl anion attack the exothermicity is grossly exaggerated without the solvent and for the dissociation of the hydroxyl O-H bond no low-lying transition state was found for the gas phase complex. One important conclusion drawn from these facts is that the final acetaldehyde formation should occur by direct proton abstraction involving the solvent.