Magnesium oxide as a heterogeneous and recyclable base for the N-methylation of indole and O-methylation of phenol using dimethyl carbonate as a green methylating agent

Abstract

This work reports a mild efficient and sustainable protocol for N-methylation of indole and O-methylation of phenol using dimethylcarbonate as an environmentally safe, non-toxic, biodegradable and green methylating agent under microwave conditions. Magnesium oxide (MgO) has been employed as a heterogeneous and recyclable base for clean N-methylation of indole and O-methylation of phenol with dimethylcarbonate. Basic properties of the fresh and recycled MgO were measured by temperature programmed desorption (CO₂-TPD) analysis. The CO₂-TPD runs suggested that both strong and moderately basic sites are present on the oxide, while only the moderately basic sites are responsible for the N-and O-methylation of indole and phenol, respectively, using DMC as a methylating agent. The CO₂-TPD analysis showed that the basic sites on fresh and recycled MgO were comparable. The MgO was isolated by simple filtration and recycled efficiently without loss in activity and selectivity.