Sulfonated PEG-intercalated montmorillonite [(Mt/PEG)-SO3H] as efficient and ecofriendly nanocatalyst for synthesis of α,α'-bis(substituted benzylidene)cycloalkanones

(Montmorillonite/PEG)-SO3H nanocomposite was successfully prepared for the first time and introduced as a solid acid nanocatalyst. Initially, polyethylene glycol (PEG) polymeric chains were intercalated into interlayer spaces of montmorillonite. The resulting Mt/PEG nanocomposite with good mechanical and thermal stability was chosen as a useful clay mineral/polymer support for further modification with chlorosulfonic acid. Structural characterization of (Mt/PEG)-SO3H was carried out using X-ray diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) measurements, Barrett-Joyner-Halenda (BJH) analysis, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier-transform infrared (FT-IR) spectroscopy. The results showed that PEG chains were intercalated into the clay mineral layers and that the Mt/PEG nanocomposite was successfully sulfonated. (Mt/PEG)-SO3H nanocomposite exhibited high specific surface area and good stability up to around 150 A degrees C, showing excellent potential for application as a recyclable nanocatalyst. (Mt/PEG)-SO3H was used as an efficient and ecofriendly solid acid nanocatalyst for preparation of alpha,alpha'-bis(substituted benzylidene)cycloalkanones under solvent-free conditions, leading to many interesting findings. The excellent conversion values confirm that the catalyst has strong and sufficient acidic sites, which are responsible for its catalytic performance. The reaction under mild conditions (room temperature) with excellent yield, catalyst recyclability (up to ten times), and simple work-up procedure represent useful advantages of (Mt/PEG)-SO3H for catalysis. Moreover, the reaction could be scaled up to 10 and 15 mmol scales.