Synthesis and stability of L-tryptophan adsorbed on Ti/MCM-41 as a catalyst for the regioselective aminolysis of styrene oxide

• Synthesis and characterization of L-tryptophan adsorbed on the surface of Ti/MCM-41.
• L-tryp≡Ti/MCM-41 as a heterogeneous catalyst for the aminolysis of styrene oxide.
• High to excellent activity and regioselectivity under microwave irradiation.
• Stability of the catalyst and its ease of recovery and reuse for several cycles.

L-tryptophan is adsorbed on the titania surface of Ti/MCM-41 (L-tryp≡Ti/MCM-41) as a novel material via two steps. Ti/MCM-41 was first prepared by grafting TiCl4 on activated MCM-41 mesoporous silica in an anhydrous THF. Subsequent adsorption of L-tryptophan on the surface of grafted Ti sites from an aqueous solution afforded L-tryp≡Ti/MCM-41. Characterization of the material was carried out with thermogravimetric and differential thermogravimetric analyses, powder X-ray diffraction, BET and BJH nitrogen adsorption–desorption methods, Fourier transform infrared, UV–Visible, and energy dispersive X-ray spectroscopes. The results indicate that the adsorption of L-tryptophan on the surface of Ti/MCM-41 occurred. L-tryp≡Ti/MCM-41 was applied successfully as a heterogeneous catalyst for the ring opening of styrene oxide with aniline derivatives and demonstrated high to excellent activity and regioselectivity under microwave irradiation and solvent-free conditions. This thermal-resistant catalyst can be recycled at least five times without appreciable loss of activity, which confirms the strong adsorption of L-tryptophan on Ti/MCM-41.

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