Direct Green Iodination of Phenol over Solid Acids

Examination of several solid acid catalysts of different nature (acid resins, zeolites, mixed oxides, Nb-oxide, and Nb-phosphate) was performed for the direct iodination reaction of phenol by using molecular iodine. The experiments were carried out in mild and green conditions (50 °C at ambient pressure) in methanol in the presence of H2O2 as oxidant agent. Iodine was introduced in reduced amount, stoichiometric for the formation of di-iodinated phenol, to obtain information on the regio-selectivity of the iodination reaction. The catalysts proved to be all efficient for the introduction of iodine into the aromatic substrate, yielding mono-, di-, and tri-iodo derivates. Different selectivity distributions to the iodo-compound formed were observed over the different catalysts. Catalysts could be grouped into distinct families on the basis of their ortho/para orientation.