Synthesis of the nano-magnetic ionic liquid based on caffeine and its catalytic application in the synthesis of xanthenes

Greening up organic reactions with caffeine: applications, recent developments, and future directions

Numerous studies in the field of alkaloid chemistry have provided researchers with valuable insights into their unique properties as catalysts. Among the diverse natural catalysts, caffeine has emerged as a green, expedient, and biodegradable catalyst with high efficiency and applicability. Interest in using caffeine as a catalyst has burgeoned over the past few years with its role in diverse multicomponent reactions. Preparation of its imidazolium salts and further conversion to Nitrogen Heterocyclic Carbene (NHC) ligands and ionic liquids offers new paradigms. Caffeine has also played a multifaceted role as a support material in influencing the structural properties of nanoparticles. We hope that the chemistry of caffeine and its applications for sustainable organic transformations discussed in this review will stimulate new thinking and open new avenues in this field.

Accelerated synthesis of 1,8-dioxo-octahydroxanthene and 1,8-dioxo-decahydroacridine derivatives using dendritic mesoporous nanosilica functionalized by hexamethylenetetramine: a novel nanocatalyst

Xanthene and acridine derivatives are interesting organic compounds that are used in different research fields like biomedicine and pharmaceutical science. However, applied catalysts for their synthesis have some limitations such as long reaction times, the need for harsh conditions and low yield. So, discovery of novel catalysts for the synthesis of xanthene and acridine derivatives is highly demanded. To overcome the limitation of previous methods on the efficient synthesis of 1,8-dioxo-octahydroxanthene and 1,8-dioxo-decahydroacridine derivatives, a green heterogeneous organic nano-catalyst (Cu@KCC-1-nPr-HMTA) was synthesized by covalent attachment of hexamethylenetetramine to the cavities and channels of dendritic mesoporous nanosilica (KCC-1). The prepared nano-catalyst was identified using various spectroscopic and microscopic methods including scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), X-ray energy diffraction (EDX), EDX mapping and nitrogen adsorption-desorption analysis (BET-BJH). The prepared green nano-catalyst showed a spherical and dendritic structure with a surface area of 65.699 m2 g-1, average pore size of 40.78 nm and pore volume of 0.66 cm3 g-1. Also, Cu@KCC-1-nPr-HMTA has many chemo-active sites for the condensation reaction and was used as an efficient nano-catalyst towards one-step synthesis of 1,8-dioxo-decahydroacridine and 1,8-dioxo-octahydroxanthene derivatives from the reaction of aromatic aldehydes, dimedone, and ammonium acetate under solvent-free conditions. Short reaction times of 1 to 5 minutes for 1,8-dioxo-decahydroacridine and 30 to 55 minutes for 1,8-dioxo-octahydroxanthene derivatives, high yields and mild reaction conditions are advantages of the proposed synthetic method. It is hoped that the engineered nano-catalyst will be used for the synthesis of other organic compounds in the future.

Confinement Effects on the Magnetic Ionic Liquid 1-Ethyl-3-methylimidazolium Tetrachloroferrate(III)

Confinement effects for the magnetoresponsive ionic liquid 1-ethyl-3-methylimidazolium tetrachloroferrate(III), [C2mim]FeCl4, are explored from thermal, spectroscopic, and magnetic points of view. Placing the ionic liquid inside SBA-15 mesoporous silica produces a significant impact on the material’s response to temperature, pressure, and magnetic fields. Isobaric thermal experiments show melting point reductions that depend on the pore diameter of the mesopores. The confinement-induced reductions in phase transition temperature follow the Gibbs–Thomson equation if a 1.60 nm non-freezable interfacial layer is postulated to exist along the pore wall. Isothermal pressure-dependent infrared spectroscopy reveals a similar modification to phase transition pressures, with the confined ionic liquid requiring higher pressures to trigger phase transformation than the unconfined system. Confinement also impedes ion transport as activation energies are elevated when the ionic liquid is placed inside the mesopores. Finally, the antiferromagnetic ordering that characterizes unconfined [C2mim]FeCl4 is suppressed when the ionic liquid is confined in 5.39-nm pores. Thus, confinement provides another avenue for manipulating the magnetic properties of this compound.

NiII NPs entrapped within a matrix of l-glutamic acid cross-linked chitosan supported on magnetic carboxylic acid-functionalized multi-walled carbon nanotube: a new and efficient multi-task catalytic system for the green one-pot synthesis of diverse heterocyclic frameworks

In the present study, a new l-glutamic acid cross-linked chitosan supported on magnetic carboxylic acid-functionalized multi-walled carbon nanotube (Fe₃O₄/f-MWCNT-CS-Glu) nanocomposite was prepared through a convenient one-pot multi-component sequential strategy. Then, nickel^II nanoparticles (Ni^II NPs) were entrapped within a matrix of the mentioned nanocomposite. Afterward, the structure of the as-prepared Fe₃O₄/f-MWCNT-CS-Glu/Ni^II nanosystem was elucidated by various techniques, including FT-IR, PXRD, SEM, TEM, SEM-based EDX and elemental mapping, ICP-OES, TGA/DTA, and VSM. In the next part of this research, the catalytic applications of the mentioned nickel^II-containing magnetic nanocomposite were assessed upon green one-pot synthesis of diverse heterocyclic frameworks, including bis-coumarins (3a–n), 2-aryl(or heteroaryl)-2,3-dihydroquinazolin-4(1H)-ones (5a–r), 9-aryl-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones (7a–n), and 2-amino-4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitriles (9a–n). The good-to-excellent yields of the desired products, satisfactory reaction rates, use of water solvent or solvent-free reaction medium, acceptable turnover numbers (TONs) and turnover frequencies (TOFs), along with comfortable recoverability and satisfying reusability of the as-prepared nanocatalyst for at least eight successive runs, and also easy work-up and purification procedures are some of the advantages of the current synthetic protocols.

In this research work, an Fe₃O₄/f-MWCNT-CS-Glu/Ni^II hybrid nanocomposite was synthesized, characterized, and used as a new and efficient multi-task catalytic system for the green one-pot synthesis of diverse heterocyclic frameworks.