Efficient and selective microwave-assisted O-methylation of phenolic compounds using tetramethylammonium hydroxide (TMAH)

Abstract

In this study, an efficient method for O-methylation of phenolic compound using tetramethylammonium hydroxide (TMAOH) as a new alkylating agent under microwave irradiation was developed. Ethanol was selected as a green reaction media to accomplish this protocol under environmentallybenign conditions. Less than half hour time is needed to obtain good to excellent yields of products at temperature of about 120°C. Using this procedure, phenolic compounds could be converted to the corresponding aryl methyl derivatives quickly. The results indicated that different phenolic compounds bearing both electron-withdrawing and electron-donating groups are O-methylated effectively using TMAOH under microwave irradiation. This novel protocol has many improvements in view point of reaction yields, selectivity and conditions compared to previous studies. Trimethylamine and water were the side products of O-methylation reaction which can be recovered easily from the product mixture. This methodology showed high selectivity for O-methylation and no C-methylated products were observed.

Keywords

• microwave-assisted
• o-methylation
• phenolic compound
• tetramethylammonium hydroxide