Heterogeneous Catalyzed Benzylic Acetoxylation of Methylated Aromatic Hydrocarbons.

The palladium-catalyzed acetoxylation of toluene to benzyl acetate is highly dependent on particle size. The rate of reaction is highest with 30-35 A particles corresponding to a 0.33 dispersion. Catalysts prepared and reduced by controlled methods before being contacted with the reaction medium, ex situ catalysts, were found to yield lower reaction rates than catalysts prepared in the reaction medium, in situ. Potassium ion encapsulation in palladium during in situ preparation is a possible explanation for this result. Tin is required to reduce Pd2+ to Pd0 in the in situ system, but is not required for the ex situ catalyst. The improvement in activity of the ex situ catalyst in the presence of tin may be due to the reducibility of Sn4+ to Sn2+ during oxygen-poor regimes. Results obtained with diverse methylated aromatic hydrocarbons indicate that the aromatic ring interacts with the palladium surface via π-donation before oxidation occurs.