Simple, non-catalytic permethylation of catechol derivatives in subcritical and supercritical water

Environmentally benign, non-catalytic, simple, and complete aromatic ring methylation of catechol derivatives by using 1,3,5-trioxane as the source of methyl groups was investigated in subcritical and supercritical water and under solvent-free conditions. Irrespective of the presence of subcritical and supercritical water as a reaction medium, catechol and 4-methylcatechol afforded the permethylation product 3,4,5,6-tetramethylcatechol. Only a small amount of 3,4,5,6-tetramethylcatechol (2% yield) was obtained under solvent-free conditions at 400 °C for 10 min. However, supercritical water considerably accelerated the formation of 3,4,5,6-tetramethylcatechol (13% yield) under the conditions of 400 °C, 10 min, and 0.35 g/mL water density.

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► An environmentally benign, simple, non-catalytic method for permethylation of catechol derivatives in subcritical and supercritical water.
► The temperature, reaction time, and water density dependence of permethylation of catechol derivatives.
► Permethylation of catechol derivatives in a very short reaction time (10 min) under the conditions of 400 °C and 0.35 g/mL water density in supercritical water.