Alkaline Ionic Liquids Immobilized on Protective Copolymers Coated Magnetic Nanoparticles: An Efficient and Magnetically Recyclable Catalyst for Knoevenagel Condensation

Abstract

A novel three-layered catalyst was successfully synthesized by the copolymerization of divinylbenzene and vinyl benzyl chloride in the presence of 3-mercaptopropyltrimethoxysilane-functionalized magnetic nanoparticles (MNPs) followed by quaternization reaction with N-propyl imidazole and alkaline ion exchange, aiming at improving the recyclability of MNPs supported catalysts. The results obtained by FTIR, TG/DTA, SEM, TEM, DLS, and VSM showed that the prepared catalyst consisted of a catalytic layer, protective layer, and magnetic core. The investigation of catalytic performance indicated that the catalyst displayed a remarkable activity for Knoevenagel condensation due to the large amount of OH − ions loading on the surface and a lower activation energy than that of NaOH, but it was sensitive to the polarity of solvent. Furthermore, the existence of a protective layer incorporated between the MNPs and the catalytic layer provided a good way to avoid the corrosion of magnetic nanoparticles, and the catalyst exhibited good stability in alkaline medium. The catalyst could be recycled by an external magnet at least six times without significant change.

Room temperature ionic liquid promoted improved and rapid synthesis of highly functionalized imidazole and evaluation of their inhibitory activity against human cancer cells

“…b Reaction conditions : (B) Benzoins (1 mmol), aldehydes (1 mmol), anilines (1 mmol), and NH 4 OAc (2.10 mmol) in medium (5 ml), stirred at Room Temperature. All products were characterized by a comparison of their spectroscopic data (FT‐IR, 1 H NMR) with those reported in the literature 13–59 . b Isolated yields c : no condensation.…”

“…e.g., high thermal stability, excellent chemical stability, negligible vapor pressure, extensive liquid temperature assortment, easy recyclability, and reliable solvent supremacy for a wide variety of inorganic and organic compounds by remodeling of anions and cations, the characteristics of ionic liquids can be derived in several ways up to the present time, 31–34 and several functional ionic liquids have been prepared for various purposes 35,36 . Particularly, they have been extensively useful in organic/inorganic transformations as catalysts or solvents, mostly including michael's reaction, 37 aldol reaction, 38 Knoevenagel condensation, 39 coupling reaction, 40 Diels−Alder reaction, 41 oxidation, 42 and reduction 43 …”

Structural Regulation of Magnetic Polymer Microsphere@Ionic Liquids with an Intermediate Protective Layer and Application as Core–Shell–Shell Catalysts with High Stability and Activity

“…The low polarity of the PS protective layer was benefit to the inhibited H + from diffusing into the interior of the microspheres, which achieved more protection of the internal MNPs. 40 Furthermore, the mass loss of MNPs in the supernatant was quantitatively calculated after acid corrosion ( Figure 2 B). The loss of MNPs of Im[Cl]/MNPs@P(St-DVB)@P(VBC-DVB) was much lower than those of Im[Cl]/MNPs@P(VBC-DVB) and Im[Cl]/MNPs@P(VBC-St-DVB).…”

“… 39 Ren et al applied a three-layered structure to improve the activity and stability of N -propyl imidazole alkaline ion liquid@MNP catalysts. 40 Obviously, many improvements have been achieved in promoting their catalyst activity, but the methods to improve the stability of magnetic polymer microsphere supported IL catalysts are rare.…”

“…It is reasonable to introduce an inactive copolymer layer as the protective layer between the MNPs and the active catalytic layer to avoid corrosion and leakage of MNPs. 40 Herein, for the first time, a novel catalyst for a core–inactive protective layer–active catalytic layer structure was proposed. An alkaline IL catalyst supported on poly( p -chloromethylstyrene)/3-mercaptopropyltrimethoxysilane-functionalized MNP composite microspheres with polystyrene layer (Im[OH]/MNPs@P(St-DVB)@P(VBC-DVB)) was successfully synthesized ( Scheme 1 ).…”