Efficient, selective and mild oxidation of sulfides and oxidative coupling of thiols catalyzed by Pd(II)-isatin Schiff base complex immobilized into three-dimensional mesoporous silica KIT-6

Abstract

In this study, a palladium(II)-isatin Schiff base complex immobilized into three-dimensional (3D) mesoporous silica KIT-6 (Pd-isatin Schiff base@KIT-6) was synthesized and characterized by various techniques including inductively coupled plasma (ICP) and Fourier transform infrared (FT-IR) spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) technique and thermal gravimetric analysis (TGA). This new heterogeneous catalyst was successfully employed for the selective oxidation of sulfides to sulfoxides with tert-butyl hydroperoxide (tert-BuOOH) and oxidative coupling of thiols into corresponding disulfides using 30% H₂O₂ at room temperature. The products were obtained in good to excellent yields and no over-oxidation of sulfoxides and disulfides was observed. This catalytic system could also be applied for the chemo-selective oxidation of sulfides and thiols in the presence of other functional groups. The studied catalyst can be recovered easily by a simple filtration and reused five times in both oxidation reactions without a remarkable decrease in catalytic activity.

GRAPHICAL ABSTRACT

KEYWORDS:

• Palladium
• Schiff base complex
• mesoporous KIT-6
• sulfoxide
• disulfide

Acknowledgements

The support for this work by the Vali-e-Asr University of Rafsanjan is gratefully acknowledged. The authors also thank Professor Majid Moghadam from the University of Isfahan, Dr. Parvaneh Iranmanesh from Vali-e-Asr University of Rafsanjan and Dr. Zahra Pakdin-Parizi from Razavi Hospital of Mashhad for their useful helps.

Disclosure statement

No potential conflict of interest was reported by the author(s).