Carbon nanotubes grafted with sulfonated polyacrylamide as a heterogeneous catalyst for the preparation of bis(indolyl)methanes

Abstract

Multiwalled carbon nanotubes (MWCNTs) were grafted with poly(AMPS–co–AM) by free-radical polymerization of acrylamide (AM) and 2–acrylamido–2-methylpropane sulfonic acid (AMPS) monomers initiated by benzoyl peroxide (BPO). MWCNT–poly(AMPS–co–AM) was characterized by Fourier transform–infrared spectroscopy (FT–IR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Observation showed that grafting of poly(AMPS–co–AM) to MWCNTs improves solubility of MWCNTs in water, ethanol, and dichloromethane. MWCNT–poly(AMPS–co–AM) also showed good catalytic performance for the preparation of bis(indolyl)methanes and 1,8-dioxo-octahydroxanthenes through the condensation of an aldehyde with indole and 5,5-dimethyl-1,3-cycloheanedione (dimedone), respectively. MWCNT–poly(AMPS–co–AM) catalyst can be reusable for at least up to eight times without significant loss of activity.