Immobilization of Lewis acidic ionic liquid on perlite nanoparticle surfaces as a highly efficient solid acid catalyst for the solvent-free synthesis of xanthene derivatives

Abstract

In this study, perlite nanoparticles were prepared through a simple method and then modified with Lewis acidic ionic liquid (perlite NP@IL/ZrCl₄) through a two step procedure. The prepared solid acid catalyst was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and thermo gravimetric analysis (TGA). Perlite NP@IL/ZrCl₄ was used as a new solid acid, reusable and green heterogeneous nanocatalyst for the one-pot synthesis of xanthene derivatives. Synthesis of xanthenes was performed under solvent free conditions using a catalytic amount (0.005 g, 0.4 mol%) of the prepared catalyst with simple work-up and high to excellent yield of products. The reusability and high efficiency of this catalyst makes this method attractive for large scale environment-friendly operations.

Scheme 1. Solvent free one-pot synthesis of three types of xanthene derivatives in the presence of perlite NPs@IL/ZrCl₄.

Fig. 1. FT-IR spectra of (a) perlite NPs and (b) perlite NPs@IL/ZrCl₄.

Fig. 2. TGA analysis of perlite NPs IL/ZrCl₄.

Fig. 3. X-ray diffraction (XRD) pattern of (a) perlite and (b) perlite-IL/ZrCl₄ nanoparticles.

Fig. 4. SEM photographs of (a) perlite NPs and (b) perlite NPs@IL/ZrCl₄ nanoparticles.

Fig. 5. EDX of perlite NPs (a) and perlite NPS@IL/ZrCl₄ (b).

Scheme 2. Preparation of dimeric xanthenes.

Scheme 3. Suggested mechanism for the one-pot synthesis of xanthene derivatives in the presence of perlite NPs@IL/ZrCl₄ nanoparticles.

Fig. 6. Reusability of perlite NPs@Il/ZrCl₄.

Fig. 7. FTIR (a) and SEM image (b) of recovered catalyst.

Scheme 4. Preparation of perlite NPs@IL/ZrCl₄.