Easy functionalization of carbon nano-onions with disulfides and their use as recyclable heterogeneous organocatalysts

Abstract

A facile functionalization of carbon nano-onions (CNO), through an atom economical one-step process, with a series of different generation (2.0, 2.5, and 3.0G) poly(amidoamine) (PAMAM) dendrimers with a cystamine core and endowed with either methyl ester or amino groups in the periphery has been reported. The radical addition reaction onto CNO surface, after the homolytic rupture of the S-S bond of cystamine, afforded CNO-PAMAM hybrids, which were extensively characterized using various analytical and spectroscopic techniques such as thermogravimetric analysis (TGA), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, solid state 13C NMR, Raman, X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and zeta potential (ZP). Morphological and textural properties were also investigated by high-resolution transmission electron microscopy (HRTEM) analysis and N2 adsorption/desorption isotherms. Furthermore, the presence and availability of -NH2 groups has been demonstrated by applying the functionalized CNO with PAMAM 2.0G and 3.0G as heterogeneous and recyclable organocatalysts in the one-pot three-component synthesis of 2-amino-4H-chromene derivatives.