Oxidative coupling of 2-aminophenol to 2-amino-phenoxazine-3-one catalyzed by organotin (IV)–copper (I) cyanide coordination polymers as heterogeneous catalysts
Abstract The activity of organotin (IV)–copper (I) cyanide coordination polymers [Ph 3 SnCu (CN) 2 · L] where L = 1,2-bis(4-pyridyl)ethane (bpe) 1 , 4,4′-bipyridine (bpy) 2 , methylpyrazine (mepyz) 3 or trans-1,2-bis(4-pyridyl)ethene (tbpe) 4 has been investigated as heterogeneous catalysts for the biomimetic oxidative coupling of 2-aminophenol (OAP) to 2-aminophenoxazine-3-one (APX). The rate of OAP consumption was determined by measuring the amount of dioxygen consumed using a gas burette. All the coordination polymeric catalysts showed high activity for auto-oxidation of OAP. The coordination polymer 4 has been found to be the most reactive catalyst. The rate of auto-oxidation reaction of OAP catalyzed by the coordination polymer 4 has been found to increase with increasing the pH from 7 to 9 then decreased at higher pH. The rate of auto-oxidation reaction showed linear dependence on catalyst concentration and pressure of dioxygen. The rate of reaction has been found to fit a Michaelis–Menten kinetic model for saturation of catalyst sites with increasing OAP concentration. The catalyst 4 showed no deactivation after six runs.