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

Abstract

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.3

One-step and non-catalytic intramolecular redox reactions of conjugated all E-dienals to non-conjugated Z-enoic acids in subcritical water

“…By employing these remarkable properties, intriguing reactions were reported, such as the Beckmann rearrangement of cyclohexanone oxime [20], pinacol rearrangement of 2,3-dimethyl-2,3-butanediol [21], and Cannizzaro reaction of formaldehyde [22], acetaldehyde [23,24], and benzaldehyde [25] in SCW without any catalyst. Through the researches, we recently disclosed a series of unique reactions, such as non-catalytic green oxidation of alcohols in SCW without any oxidant to give ketones and hydrogen gas [26], highly selective non-catalytic Oppenauer oxidation of alcohols in SCW [27], the first direct observation of radical species in sub-CW by means of ESR [28], easy permethylation of catechols in SCW [29], and effective aldol reactions in sub-CW [30].…”