Room Temperature Synthesis of Mequinol by Using Ionic Liquids as Homogeneous Recyclable Catalysts

For synthesis of Mequinol (4-methoxy phenol), two acidic ionic liquids based on imidazolium cation (BMSIL and IMSIL) synthesized and characterized with FT-IR, 1H NMR and CHNS analyses. Then, the Baeyer–Villiger oxidation of para-anisaldehyde was studied with these ionic liquids, as the catalysts. The results showed that the BMSIL with more Brønsted acidic functions had higher catalytic activity than IMSIL and even sulfuric acid at room temperature. Furthermore, the different reaction parameters were studied and maximum conversion (99%) and selectivity (95%) of Mequinol was observed by using 5% BMSIL as catalyst, H2O2 (30% solution) as oxidant, Methanol as solvent at 3.5 h, and room temperature condition. Also, we investigated the effect of different substituents in the aromatic ring of benzaldehyde and various solvents on the catalytic activity of BMSIL ionic liquid as the best catalyst in the oxidation of aromatic aldehydes. The results show that the protic solvent and electron-donating substituents in para position of benzaldehyde favor the phenol product.