Multistep electron transfer catalytic system for the oxidative carbonylation of phenol to diphenyl carbonate

Abstract

The oxidative carbonylation of phenol to diphenyl carbonate is catalyzed by palladium salts in combination with a cocatalyst such as p-benzoquinone (BQ) or a salt of Co, Mn, Cu. The addition of a surfactant such as tetrabutylammonium bromide makes the catalytic system more efficient. The role of each component in the catalytic system is discussed. A catalytic cycle is proposed where, in the first step, diphenylcarbonate is formed from phenol and CO with concomitant reduction of Pd(II) to Pd(0) and formation of two protons. p-Benzoquinone, which is reduced to hydroquinone, in the presence of protons, reoxidizes Pd(0) to Pd(II) while the metal cocatalyst is reduced by hydroquinone which is reoxidized to p-benzoquinone. Oxygen and protons, arising from the last reaction, close the cycle with reoxidation of the reduced metal cocatalyst and formation of water.