Osmium(VIII)/palladium(II) catalysis of cerium(IV) oxidation of allyl alcohol in aqueous acid

Summary Catalysis of the Ce^IV-allyl alcohol (AA) reaction in acid solution depends both on the of rate enhancement and product distribution on the catalyst used: Os^VIII results mainly in acrolein, whereas Pd^II gives acrylic acid. The rate laws in the two cases also differ:viz., Equations 1 and 2K₁ is the equilibrium constant of formation of the Os^VIII-allyl alcohol complex and k₁ is the rate constant of its oxidation by Ce^IV; K₂ is the equilibrium constant for the formation of the Ce^IV-Pd^II-allyl alcohol complex and k₂ is its rate constant of decomposition. Rate = K₁k₁Ce^IV]AA]Os^VIII]/(1+K₁AA]) (1) Rate = K₁k₁Ce^IV]Pd^II]/(1+K₂Ce^IV]) (2)While Os^VIII is effective in H₂SO₄ solution, aqueous HClO₄ is needed for Pd^II. Both reactions proceed through formation of catalyst-allyl alcohol complexes with participation of free radicals. The details of these observations are discussed.