Stereochemistry and Mechanism for the Palladium( 11)-Catalyzed Oxidation of Ethene in Water (the Wacker Process)

Abstract

Palladium(I1)-catalyzed oxidation of specifically deuterated ethenes in water in the presence of cupric chloride and chloride ion has been studied. Stereospecific formation of threo- 1,2-dideuterio-2-chloroethano(lt hreo-3)f rom (E) -1 ,2-dideuterioethene ((E)-2) indicates that the hydroxypalladation step in the Wacker oxidation is a trans process. Generation of an erythro-P-hydroxyethylpalladium complex (6) from erythro-P-hydroxyethylmercuric chloride (5) in the presence of CuC12- LiCl also results in the formation of rhreo-3. Analyses of the deuterated products were done by microwave spectroscopy. A new (modified) mechanism is proposed, which involves reversible formation of 11 by external attack of water on 8, followed by a rate-determining dissociation of a chloride ligand from 11.