Palladium‐catalysed reactions of unsaturated compounds in non‐aqueous solvents: Synthesis of vinyl acetate via palladium salt/ethylene complexes

The reaction of ethylene with palladium acetate in acetic acid solvent produces vinyl acetate. The rate of this reaction increases considerably upon addition of small amounts of sodium acetate, lithium chloride or lithium chloride/ferric acetate to the system. The reaction is first‐order with respect to both the palladium acetate and the catalyst (NaOAc, LiCl, LiCl·Fe(OAc)3) concentration. In reactions starting from PdCl2 and NaOAc the rate was found to be proportional to the PdCl2 and NaOAc concentrations. In addition, in one case (LiCl· Fe(OAc)3) the rate was shown to be proportional to the ethylene concentration. A mechanism is proposed according to which the reaction proceeds via species of the type C2H4· PdOAcX2− ; vinyl acetate is formed through displacement of a hydrogen atom in the olefin molecule by coordinated acetate. The overall rate was found to be strongly influenced by the ligands bound to the metal; it increases in the order: The effect of ferric acetate on the rate is tentatively explained on the basis of an increased transfer of charge in the intermediate C2H4· PdOAcX2− complex. The fact that in the displacement of Cl− by acetate in the corresponding vinyl chloride complex (C2H3Cl. PdOAcCl2−) the overall rate is lower is attributed to the formation of vinyl chloride/PdOAcCl2− complexes proceeding less readily than that of ethylene complexes. In the LiCl‐catalysed reaction the formation of vinyl acetate was found to be completely inhibited at high concentrations of chloride ions with respect to palladium acetate; under these conditions ethylene is dimerized to butylenes. Depending on the conditions of the reaction various by‐products are formed: acetaldehyde, ethylidene diacetate, ethyleneglycol acetates, butenes. The formation of these products is discussed in relation with other studies. Finally, the results are presented of some studies on the oxidation with oxygen ‐ of palladium metal in acetic acid to palladium acetate.