Sulfonated hexamine ionic liquid on boehmite as a novel, robust and recoverable bifunctional catalyst in the selective oxidation of sulfides

A new protocol for the chemoselective preparation of sulfoxide using sulfonated hexamine ionic liquid on boehmite (boehmite@IL–SO₃H) as a novel, robust, and heterogeneous catalyst has been developed. At first, boehmite was obtained in aqueous media using available materials. In the second step, boehmite was modified by 3-iodopropyltrimethoxysilan and then was functionalized by hexamine toward the formation of supported ionic liquid on boehmite. In the third step, chlorosulfonic acid was added to synthesis boehmite@IL–SO₃H as the final catalyst. The obtained catalyst was characterized using TGA, XRD, SEM, EDS, FT-IR, BET, and WDX techniques. The XRD pattern showed that the crystal structure of boehmite remained stable in boehmite@IL–SO₃H after functionalization of IL–SO₃H. BET analysis showed that the surface area, pore volume, and pore diameter of this catalyst were 32.344 m²/g⁻¹, 0.1138 cm³/g⁻¹, and 14.074 nm, respectively. The BET results indicate a type V isotherm and a type H₃ hysteresis loop, indicating a flaky morphology with open pores, which is specific to the boehmite structure. Also, SEM images confirmed the BET results and showed a flaky morphology and sheet structure with a thickness of less than 50 nm for boehmite@IL–SO₃H. This catalyst was investigated in the selective oxidation of sulfide to sulfoxide under solvent-free conditions using H₂O₂ as an oxidant. The synthesized sulfoxides were confirmed by NMR spectroscopy. Boehmite@IL–SO₃H heterogeneous catalyst has benefits such as being cost-effective and recyclable.