Oxidative coupling revisited: solvent-free, heterogeneous and in water

Abstract

Fe(III) treated K-10 montmorillonite and FeCl3 (both hydrated and anhydrous) are compared as catalysts for oxidative coupling of phenol substrates under a range of conditions. While the commonly reported coupling of 2-naphthol proceeds under a range of conditions, other substrates are far less readily coupled. Counterintuitively, biphasic reactions of poorly water soluble substrates in contact with aqueous solutions of FeCl3 are the most universally applicable conditions while many homogeneous reaction mixtures yield little or no coupling product. Fe(III) treated K-10 proved to be a poor catalyst for oxidative coupling of most substrates. Comparison of coupling conditions provides a framework for optimisation of green methodologies using oxidative coupling catalysts.