Oxidation studies of phenols with cobalt(II) ion-modified silica in a liquid chromatographic reactor

Abstract

The activity of cobalt(II) ion-modified silica, a new catalyst for the oxidation of phenols with dissolved oxygen in organic solvents, has been studied in liquid chromatographic reactors using several approaches. In this reactor mode, catalyst activity can be maintained over months of repeated use while phenols are oxidized to p-benzoquinones at or below 45 °C. This approach eliminates problems of catalyst separations. Using the ideal liquid chromatographic reactor model with inert standard methods, the reaction is found to be first-order with respect to the phenolic reactants. Some pseudo-first-order rate constants have also been measured. The cobalt(II) ions bonded to silica probably function through reaction pathways similar to those of homogeneous cobalt complex catalysts for phenol oxidations. However, they are stable for long periods of time under the mild reaction conditions used here and can provide separation with concerted reaction.