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

Typical procedure:
Oxalyl chloride (0.34 mL, 4.0 mmol) is added dropwise to a solution of 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate (1.60 g, 4.0 mmol) in CH₂Cl₂ (6 ml) at -70 °C and the mixture is stirred for 30 min. Then, a solution of alcohol (2.0 mmol) in CH₂Cl₂ (3 mL) is added dropwise at -70 °C and stirred for 30 min. Triethylamine (1.66 mL, 12 mmol) is added dropwise at -70 °C and the mixture is stirred for 1 h at -70 °, 1.5 h at -60 °C, and then -50 °C for 1 h. Finally, the mixture is warmed to room temperature and stirred for 2 h. The reaction mixture is quenched with H₂O (10 mL), neutralized (pH = 6 to 7) with 1 M HCl aqueous solution, and extracted with diethyl ether (40 mL × 2). The organic layer is washed with water (10 mL), dried over Na₂SO₄, and filtered. After removal of the solvent, the desired aldehyde or ketone is obtained.

Recovery and recycling of ion-supported methyl sulfoxide: After the above extraction, the aqueous layer is concentrated in vacuo. After the addition of aqueous saturated NaHCO₃ solution, the ion-supported methyl sulfide is extracted with CHCl₃ (40 mL × 3). The organic layer is dried over Na₂SO₄ and filtered. After removal of the solvent, the residue is washed with diethyl ether (10 mL × 3), and concentrated in vacuo to give the ion-supported methyl sulfide in 73% yield. The methyl sulfide is quantitatively oxidized to 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate according to the literature.¹⁾