Correlation between the Basicity of Solid Bases and their Catalytic Activity towards the Synthesis of Unsymmetrical Organic Carbonates.

Abstract

The correlation between the basic properties of solid catalysts and the reaction rate of the selective synthesis of unsym. org. carbonates via direct condensation of di-Et carbonate (DEC) and alcs. was investigated. A detailed kinetic study of the transesterification of 1-phenylethanol and DEC was made with catalysts with different basic strengths. The solids included fluorinated hydrotalcite, MgLa mixed oxides, CsF (pure or supported on alpha- and gamma-aluminas), KF (pure or supported on alpha- and gamma-aluminas), anatase, rutile, and zirconia. Basic properties were detd. by the adsorption of CO2, measured by gravimetry coupled with mass spectrometry and by calorimetry. Both techniques show a higher basicity for MgLa mixed oxides. The rate of the reaction was roughly proportional to the no. of strongly basic sites present on the catalyst, except for CsF/alpha-Al2O3, which showed higher activity for several different substrates in spite of a lower no. and strength of basic sites. This is attributed to the high nucleophilicity of the alcoholate formed as an intermediate. The addn. of water to the reaction medium induces two effects: inhibition of the reaction and the promotion of etherification of the substrate by ethanol as a side reaction. The catalysts can be reused several times with a small loss of activity