Benzylation of Aromatic Compounds Catalyzed by 3-Methyl-1-sulfonic Acid Imidazolium Tetrachloroaluminate and Silica Sulfuric Acid under Mild Conditions

Abstract

In this work, efficient procedures for benzylation of a range of aromatic compounds by benzyl acetate in the presence of catalytic amounts of 3-methyl-1-sulfonic acid imidazolium tetrachloroaluminate ([Msim]AlCl₄) or silica sulfuric acid (SSA) under mild conditions are described. Simple methodology, easy workup procedure, clean reaction and reusability of the catalyst are some advantages of this work.

Key words

benzylation - benzyl acetate - 3-ethyl-1-sulfonic acid imidazolium tetrachloroaluminate - silica sulfuric acid

• References and Notes

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• 22 General Procedure for the Synthesis of Diarylmethanes Using [Msim]AlCl₄ : To a mixture of aromatic substrate (1 mmol) and benzyl acetate (1 mmol) was added [Msim]AlCl₄ (0.017 g, 5 mol%) and the mixture was heated to 70 °C for the appropriate time (Table 3). After completion of the reaction, as monitored by TLC, the reaction mixture was cooled to r.t. and CH₂Cl₂ (2–5 mL) was added to separate the catalyst. After filtration, the pure product was obtained using plate chromatography on silica gel with n-hexane–EtOAc (10:2) as eluent. Note: In some cases, the reaction was carried out in CH₂Cl₂ (5 mL) at reflux (Table 3, entries 4–6, 9 and 10). General Procedure for the Synthesis of Diarylmethanes Using SSA: To a mixture of aromatic substrate (1 mmol), and benzyl acetate (1 mmol), silica sulfuric acid (0.054 g, 7 mol%) was added and the mixture was heated to 80 °C for the appropriate time (Table 3). After completion of the reaction, as monitored by TLC, the reaction mixture was cooled to r.t. Absolute EtOH (2–5 mL) was added and the mixture was filtered to separate the catalyst. The pure product was obtained using plate chromatography on silica gel with n-hexane–EtOAc (10:2) as eluent. Note: In some cases, the reaction was carried out in CH₂Cl₂ (5 mL) at reflux (Table 3, entries 4–6, 9 and 10).