Preparation of immobilized hexamine on Fe3O4/SiO2 core/shell nanoparticles: a novel catalyst for solvent-free synthesis of bis(indolyl)methanes

Abstract

Hexamethylenetetramine covalently immobilized on silica-coated magnetic nanoparticles is prepared and characterized by XRD, FT-IR, SEM, and VSM. According to SEM pictures, the nanoparticles are mostly spherical in shape, and their size is approximately 46 nm. The catalytic performance of these magnetic nanoparticles for the synthesis of bis(indolyl)methanes was investigated. The catalyst was readily recycled by the use of an external magnetic field and can be reused four times without significant loss of activity. Graphical AbstractKeywords Magnetically retrievable Á Nano-hybrid Á Bis(indolyl)methanes Á Solventfree Á Silica Á Hexamethylenetetramine

Fe3O4/granular activated carbon as an efficient three-dimensional electrode to enhance the microbial electrosynthesis of acetate from CO2

“…16 Although bare Fe 3 O 4 has been utilized for general electrochemical applications, 17,18 Fe 3 O 4 particles have the drawback of aggregation due to nanometer-scale and magnetic effects, which can remarkably decrease their catalytic activity. 19 GAC is commonly used as a carrier for microorganisms and catalysts because it has no biological toxicity, high surface area, and numerous pores that are available for modications or adsorption. 20 It has been reported that Fe 3 O 4 nanoparticles grown on the carbon supports 21,22 have better catalyst dispersibility to enhance the performance of microbial fuel cells (MFC).…”

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

“…This protocol, while employing the identical optimum reaction conditions with Ramshini’s method, managed to reduce the reaction times to 10 minutes with 10 mg of the catalyst and could also facilitate the reaction of ketones. This improved upon the previously known nano-iron oxide methodologies without sacrificing their already satisfying product yields, the recyclability of the nanocatalyst or their environmentally benign aspects, such as the solvent-free conditions without, however, addressing the need for conventional heating that still presented an issue [ 111 ].…”

“…The main drawback of the method, however, is the necessity of conventional heating and solvent compared to other methodologies [109,110]. At the same time, Yavari and his research group also studied the use of hexamine, in place of NPS-γ-Fe 2 O 3 , immobilized on Fe 3 O 4 and coated with SiO 2 [111]. This protocol, while employing the identical optimum reaction conditions with Ramshini's method, managed to reduce the reaction times to 10 minutes with 10 mg of the catalyst and could also facilitate the reaction of ketones.…”

“…Under microwave irradiation, chemical reactions are accelerated by the absorption of microwaves by polar organic molecules, which renders reactions that are not catalyzed with conventional heating possible. This was made apparent in Karthikeyan's and Bankar's nanocatalysis protocols for the synthesis of BIMs, who incorporated MW, which led to an impressive surge in reaction rates [105][106][107][108][109][110][111][112][113][114][115][116][117]. The prominent benefits of the microwave approach over traditional protocols, are low energy consumption, accelerated reaction rates, avoiding the use of toxic organic solvents and ease of regulation of the reaction parameters [127,128].…”

Synthesis of Bis(indolyl)methanes Using Fe3O4 Nanoparticle as a Robust, Efficient and Magnetically Recoverable Catalyst Under Solvent-Free Conditions

“…41 Ademais, no que se refere à síntese dos BIMs, muitas estratégias sintéticas são descritas quanto ao uso do Fe3O4 nano como suporte para a imobilização de metais de transição, sendo esses materiais utilizados como catalisadores magnéticos nessas reações de alquilação de Friedel-Crafts. [42][43][44][45][46][47] No entanto, o uso direto de Fe3O4 nano como catalisador para esse tipo de reação ainda é raro na literatura. 43 Dessa forma, visando ao desenvolvimento de uma metodologia sintética eficiente, robusta e sustentável para a preparação de compostos BIMs, descrevemos neste artigo o emprego direto do Fe3O4 nano como catalisador da reação de substituição eletrofílica (alquilação de Friedel-Crafts) de indóis e aldeídos.…”