Nano-Fe3O4 encapsulated-silica particles bearing sulfonic acid groups as an efficient, eco-friendly and magnetically recoverable catalyst for synthesis of various xanthene derivatives under solvent-free conditions

Zr(HSO4)4: Green, efficient and reusable catalyst for one-pot synthesis of 1,8-dioxooctahydroxanthene under solvent-free conditions

Many methods have been used to synthesize xanthene derivatives using different catalysts. However, some of these methodologies have not been entirely satisfactory. Most of the mentioned methods have disadvantages such as low yields, prolonged reaction times, harsh reaction conditions and the requirement of expensive catalysis and use of toxic organic solvent. In this research, a green and highly efficient procedure for the one-pot synthesis of 1,8-dioxo-octahydro-xanthenes has been developed. Zr(HSO₄)₄ catalyst was used as an efficient and recoverable catalyst for synthesis of 1,8-dioxo-octahydro-xanthene derivatives via cyclocondensation of dimedone and aromatic aldehydes in solvent-free conditions. There are no examples of the use of Zr(HSO₄)₄ for the synthesis of 1,8-dioxo-octahydro-xanthene derivatives. The present method offers several advantages such as green, highly efficient, recoverable, reusable, simple work-up and simple purification of products. The structure of the synthesized products was confirmed by Fourier Transform Infrared (Ft-IR) and Proton nuclear magnetic resonance (¹HNMR) analyzes. The antibacterial activity of the synthesized compounds was determined by agar disk diffusion method against gram-positive (S. aureus bacteria) and gram-negative (E. coli bacteria) microorganisms. Among the synthesized compounds (3a-3j), 3h compound showed the highest antibacterial effect by forming an inhibitory diameter zone of 15 mm around the disc containing 2000 mg of 3h-compound against gram-positive (S. aureus bacteria).

1. Use of Zr(HSO₄)₄ as a green and highly efficient and reusable heterogeneous catalyst.

2. Under solvent-free condition.

3. Simple work-up and Simple purification of products.

Eco-friendly and enhanced colorimetric detection of aluminum ions using pectin-rich apple extract-based gold nanoparticles

Aluminum ions are very toxic to human health, especially in relation to neurodegenerative diseases. However, conventional methods of detecting such toxic ions suffer from the use of poisonous chemical probes and complex processes. Herein, we report an eco-friendly and enhanced colorimetric method of aluminum ion detection using green-synthesized gold nanoparticles (AuNPs) from apple (Malus domestica) extract. The apple extract-based AuNPs (AX-AuNPs) contain abundant pectin different from citrate-based AuNPs. The pectin-rich AX-AuNPs improved the sensitivity of the colorimetric detection of aluminum ions. The detection limit was about 20 μM both in artificial and drinking water-based real samples. Interestingly, it is turned out that the AX-AuNPs were aggregated naturally after the chemical assay because of solution getting decayed. For the environmental perspective, it was great that the lump of AX-AuNP aggregates could easily be removed from the solutions before solution discard. Overall, our results indicate that AX-AuNPs offer a high-selectivity, enhanced colorimetric detection of aluminum ions in a short time (less than 1 min), based on an eco-friend synthesis and disposal manner of AuNPs.

Silica–sulfuric acid and alumina–sulfuric acid: versatile supported Brønsted acid catalysts

–SO3H functionalized silica and alumina have emerged as efficient and eco-compatible heterogeneous solid acid catalysts for the construction of various important molecular skeletons.

Application of cyclohexane-1,3-diones for six-membered oxygen-containing heterocycles synthesis

Cyclohexan-1,3-dione derivatives are versatile scaffolds for the synthesis of a variety of value-added organic molecules including heterocycles and natural products. Six-membered oxygen heterocycles prepared from cyclohexan-1,3-diones are of much importance as they are intermediate for the synthesis of a number of natural products and several other valuable bioactive molecules which shows anti-viral, anti-bacterial, analgesic, antimalarial, anti-inflammatory, anti-allergic, anti-tumor and anti-cancer activities. These advantages have inspired us to write a detailed survey on the newly developed methods which are very essential in the construction of six-membered oxygen heterocycles. Further, the versatility in the chemistry of cyclohexan-1,3-dione and its derivatives is due to the presence of highly active methylene moiety and its active di-carbonyl groups. Recently, reactions of cyclohexane-1,3-dione and its derivatives with other substrates for instance aldehydes, malononitriles, NMSM, chalcones, isatin etc. have been established for the construction of a variety of six-membered oxygen heterocycles. The studies reported in this review article involved the synthesis of six-membered oxygen-containing heterocycles which includes 4H-chromen-5(6H)-one, 2H-xanthen-1(9H)-one, 2H-xanthen-1,8(5H,9H)-dione, 6H-chromen-2,5-dione derivatives and natural products having six-membered oxygen heterocycles from cyclohexane-1,3-dione and its derivatives as one of the substrate.

Immobilized copper-layered nickel ferrite on acid-activated montmorillonite, [(NiFe2O4@Cu)(H+-Mont)], as a superior magnetic nanocatalyst for the green synthesis of xanthene derivatives

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.

In this study, the catalytic activity of the prepared (NiFe₂O₄@Cu)(H⁺-Mont) MNPs was studied towards the synthesis of dibenzo[b,i]xanthene tetraones 3(a–k) and hexahydroxanthene diones 5(a–k).

Ag-doped nano magnetic γ-Fe2O3@DA core–shell hollow spheres: an efficient and recoverable heterogeneous catalyst for A3 and KA2 coupling reactions and [3 + 2] cycloaddition

An effective protocol for the fabrication of Ag-doped nano magnetic γ-Fe₂O₃@DA core–shell hollow spheres (h-Fe₂O₃@DA/Ag) by a simple hydrothermal method is demonstrated without any templates in the reaction system.