ABSTRACT
In this study, the synthesis of a new class of magnetic clay-based nanocomposites by bridging of sulfonyl groups between copper-immobilized nickel ferrite (NiFe2O4@Cu) and activated montmorillonite is described. Synthesis of the clay nanocatalyst was carried out via the activation of montmorillonite by ClSO3H to afford sulfonated montmorillonite. The modified montmorillonite was then reacted with copper-layered nickel ferrite to afford the magnetic clay nanocomposite [(NiFe2O4@Cu)SO2(MMT)]. Next, the characterization of porous materials was carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller and vibrating sample magnetometer analyses. The obtained results showed that the clay nanocomposite containing a sulfonyl-bridge has a large surface area and magnetic properties versus the prepared one without the sulfonyl groups as (NiFe2O4@Cu)(MMT). The nanostructured clay had excellent catalytic activity towards the Hantzsch synthesis of coumarin-based 1,4-dihydropyridines via one-pot and three-component condensation of 4-hydroxycoumarin, aromatic aldehydes and ammonia. All reactions were carried out in water as a green and economic green solvent within 10-45 min to affords 1,4-DHPs in high to excellent yields. Reusability of the clay nanocomposite was investigated for six consecutive cycles without significant loss of catalytic activity. Based on this study, therefore, sulfonated montmorillonite could be considered an excellent support for the immobilization of magnetic materials.
ABSTRACT
In this study, the immobilization of copper-layered nickel ferrite on the surface and in the cavities of acid-activated montmorillonite (H+-Mont) was investigated. In this context, magnetic nanoparticles (MNPs) of NiFe2O4 as the prime magnetic cores were prepared. Next, through the reduction of Cu2+ ions with sodium borohydride, the nanoparticles of Cu0 were immobilized on the nanocore-surface of NiFe2O4, and the constituent NiFe2O4@Cu MNPs were obtained. Moreover, through the activation of montmorillonite K10 (Mont K10) with HCl (4 M) under controlled conditions, the H+-Mont constituent was prepared. The nanostructured NiFe2O4@Cu was then intercalated within the interlayers and on the external surface of the H+-Mont constituent to afford the novel magnetic nanocomposite (NiFe2O4@Cu)(H+-Mont). The prepared clay nanocomposite was characterized using FTIR spectroscopy, SEM, EDX, XRD, VSM and BET analyses. The obtained results showed that through acid-activation, the stacked-sheet structure of Mont K10 was exfoliated to tiny segments, leading to a significant increase in the surface area and total pore volume of the H+-Mont constituent as compared to those of montmorillonite alone. SEM analysis also exhibited that the dispersion of NiFe2O4@Cu MNPs in the interlayers and on the external surface of acid-activated montmorillonite was carried out successfully, and the nanoparticle sizes were distributed in the range of 15-25 nm. The BET surface analysis also indicated that through the immobilization of NiFe2O4@Cu MNPs, the surface area and total pore volume of the H+-Mont system were decreased. The catalytic activity of (NiFe2O4@Cu)(H+-Mont) was further studied towards the synthesis of substituted 13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H) tetraones 3(a-k) and 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H) diones 5(a-k)via the pseudo-one-pot three-component cyclocondensation of 2-hydroxy-1,4-naphthoquinone (Lawsone)/dimedone and aromatic aldehydes in a mixture of H2O-EtOH (1 : 1 mL) as a green solvent at 80-90 °C. The (NiFe2O4@Cu)(H+-Mont) MNPs can be easily separated from the reaction mixture by an external magnetic field and reused for seven consecutive cycles without significant loss of catalytic activity.
ABSTRACT
AIM AND OBJECTIVE: Nowadays, bisdimedones and 1,8-dioxo-octahydroxanthenes are considered as biologically active materials. Due to this, the synthesis of the mentioned materials is the subject of more interest. Although most of the reported methods have their own merits, however, they generally require the use of expensive reagents, hazardous organic solvents, a tedious workup procedure and reduced recyclability of the applied catalyst system. Overcoming of the above mentioned drawbacks, therefore, encouraged us to investigate the capability of nanostructured NiFe2O4@Cu towards the synthesis of bisdimedones and 1,8- dioxo-octahydroxanthenes under green reaction conditions. MATERIALS AND METHODS: Nanoparticles of NiFe2O4@Cu were prepared via a two-step procedure including the preparation of NiFe2O4 by solid-state grinding of Ni(OAc)2·4H2O and Fe(NO3)3·9H2O in the presence of NaOH followed by the immobilization of Cu(0) on the surface of NiFe2O4 nucleus via hydrazine hydrate reduction of Cu(NO3)2·3H2O. RESULTS: After the synthesis of NiFe2O4@Cu, the catalytic activity of the Cu-nanocatalyst towards Knoevenagel reaction of aromatic aldehydes with dimedone under different reaction conditions was investigated. The examinations showed that using the molar equivalents of aromatic aldehydes (1 mmol) and dimedone (2 mmol) in the presence of 0.15 g NiFe2O4@Cu under solvent-free conditions chemoselectively afforded structurally different bisdimedone products at 60°C and 1,8-dioxo-octahydroxanthenes at 120°C. CONCLUSION: In this study, magnetically, nanoparticles of NiFe2O4@Cu were prepared and then characterized using different analyses. The catalytic activity of the prepared Cu-nanocatalyst was also studied towards solvent-free Knoevenagel condensation of aromatic aldehydes with dimedone. All the reactions were carried out within 15-240 min to afford bisdimedone and 1,8-dioxo-octahydroxanthene products in high yields.
