1-Methyl-3-[6-(methylthio)hexyl]imidazolium p-Toluenesulfonate

Typical procedure: A solution of 1-methyl-3-[6-(methylthio)hexyl]imidazolium p-toluenesulfonate (0.769 g, 2.0 mmol) and the starting alcohol (1.0 mmol) in CH₂Cl₂ (6 mL) is added to a CH₂Cl₂ (5 mL) solution of N-chlorosuccinimide (0.267 g, 2.0 mmol) at -20 or -40 °C, and the mixture is stirred for 0.5 h. Triethylamine (0.506 g, 5.0 mmol) is added to the mixture at -20 or -40 °C. The mixture is stirred at-20 or -40 °C for 14 h, quenched with H₂O (20 mL), and extracted with diethyl ether (60 mL). The organic layer is washed with H₂O (20 mL) and a saturated aqueous NaHCO₃ (30 mL×2). The organic layer is dried over Na₂SO₄ and concentrated in vacuo to give the desired aldehyde or ketone.

Recovery of 1-methyl-3-[6-(methylthio)hexyl]imidazolium p-toluenesulfonate: After the above extraction, the aqueous layer is concentrated in vacuo. Then, KI (0.332 g, 2.0 mmol), AcOH (2 mL) and TsOH· H₂O (0.379 g, 2.2 mmol) are added to the residue at room temperature. The mixture is stirred for 1 h, quenched with a saturated aqueous Na₂SO₃ (5 mL) and a saturated aqueous NaHCO₃ (5 mL), and extracted with CHCl₃ (40 mL×3). The organic layer is dried over Na₂SO₄ and concentrated in vacuo to give 1-methyl-3-[6-(methylthio)hexyl]imidazolium p-toluenesulfonate (0.646 g, 84%).