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

RSC Advances Pub Date: 2014-10-02 DOI: 10.1039/C4RA07240E

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.

Graphical abstract: 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
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