Heterogeneous Acid Catalyst Research Articles

Multicomponent Synthesis of 2,4,5-Trisubstituted Thiazoles Using a Sustainable Carbonaceous Catalyst and Assessment of Its Herbicidal and Antibacterial Potential.

Herein, a novel, biocatalyzed, and on-water microwave-assisted multicomponent methodology have been developed for the synthesis of trisubstituted thiazoles (4a-4v). The reaction was catalyzed using a sulfonated peanut shell residue-derived carbonaceous catalyst (SPWB). The developed catalyst was characterized using Fourier transform infrared (FTIR), a Brunauer-Emmett-Teller (BET) surface area analyzer, a field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX), and a particle size analyzer (PSA). The acidic sites have been established using acid-base back-titration methods. The molecular structures of all the synthesized compounds were validated using FT-IR, 1H NMR, 13C NMR, elemental, and HRMS analyses. Herbicidal potential was evaluated by using Raphanus sativus L. as a model. Furthermore, the antibacterial potential of thiazoles was evaluated against Staphylococcus aureus, Bacillus subtilis, Xanthomonas campestris, Escherichia coli, Micrococcus luteus, and Pseudomonas aeruginosa bacterial strains. The compound 4r displayed improved seed growth inhibition in Raphanus sativus L. versus a commercially available herbicide, i.e., pendimethalin. The antibacterial activity was promising against bacterial strains (MIC: 4-64 μg/mL). The compound 4r was the most potent against P. aeruginosa and S. aureus (MIC: 0.0076 μM) versus standard drug streptomycin (MIC: 0.0138 μM). Moreover, in silico studies performed with the most effective compound 4r against P. aeruginosa revealed its potential binding mode within the protein binding pocket. The biological data revealed compound 4r as a potential candidate for the development of potent herbicidal and antibacterial agents. In a nutshell, this study offers peanut shell biowaste to be a sustainable biomass for heterogeneous acid catalyst preparation and its application in the multicomponent synthesis of bioactive thiazoles, accommodating the concept of sustainable development goals and circular bioeconomy.

Unveiling the influence of open metal sites in quasi ZIF-67 for eco-friendly catalysis of solvent-free aldehyde cyanosilylation

Quasi metal–organic frameworks (Q-MOFs) containing a high density of open metal centers are considered as an effective method of expanding the effectiveness of defective MOF-based catalysts. To achieve this, quasi ZIF-67 (Q-ZIF-67), having large scale structural defects in the framework, is produced through partial deligandation of ZIF-67 under controlled thermal treatment at 310 °C in air. This generates many unsaturated cobalt centers as Lewis acid sites, and results in the coexistence of micro and meso-pores within the Q-ZIF-67 network. Subsequently Q-ZIF-67 was employed in the catalytic cyanosilylation of benzaldehyde with trimethylsilyl cyanide, resulting in the corresponding cyanohydrin within 30 min under solvent free-conditions in air at 40 °C and room temperature with TOF values of 1.62, 1.53 min−1, respectively. The related cyanohydrin product was identified via 1H NMR. Importantly, Q-ZIF-67 displayed a highly efficient heterogeneous Lewis acid catalyst for the cyanosilylation of benzaldehyde compared to the pristine ZIF-67 and related cobalt oxide. Furthermore, investigating the impact of the electron-donating and electron-withdrawing para-substitutions on benzaldehyde revealed that electron-withdrawing groups are suitable for nucleophilic reactions. It was also observed that there was no significant decrease in catalytic activity after five catalytic runs. Thus, the Q-ZIF-67 has considerable potential as environmentally friendly catalyst for wide range of practical application in aldehyde cyanosilylation reactions.

Sulphated zirconia on cyclodextrin nanosponge: A carbohydrate-based catalyst for conversion of mono-saccharides to 5-hydroxymethylfurfural

To expand the utility of cyclodextrin nanosponges for catalytic purpose, β-cyclodextrin nanosponge was prepared via melting method and then utilized as a catalyst support for the stabilization of sulphated zirconia. The resulting catalyst, denoted as CDNS-SO42−/ZrO2, was then applied as a heterogeneous acidic catalyst for conversion of fructose to 5-hydroxymethylfurfural. The results, underpinned that the catalytic activity of CDNS-SO42−/ZrO2, was superior to that of ZrO2 and SO42−/ZrO2, confirming the role of sulfonation of ZrO2 and immobilization of SO42−/ZrO2 on CDNS in catalysis. To optimize the reaction parameters and achieve maximum yield of the desired product, Response Surface Method that is an accurate procedure for appraising the impacts of the reaction variables was employed and it was found that using 35 wt% CDNS-SO42−/ZrO2 at 80 °C, HMF in 93 % yield was achieved in 45 min. Kinetic study also showed that the activation energy was 13.28 kJ/mol. Furthermore, thermodynamic parameters, i.e. enthalpy, entropy and Gibbs free energy were estimated as 10.46 kJ/mol, −150.40 J/mol and 63.58 kJ/mol respectively. Noteworthy, the catalysis was true heterogeneous, as confirmed by Hot filtration test and the catalyst could be recycled several times with low leaching of SO42−/ZrO2.

Methyl ester production process from palm fatty acid distillate using hydrodynamic cavitation reactors in series with solid acid catalyst

This study aims to optimize the reduction of free fatty acids (FFAs) in palm fatty acid distillate (PFAD) using hydrodynamic cavitation reactors (HCRs) in series and a solid acid catalyst for biodiesel production. Hydrodynamic cavitation is used to accelerate the esterification of FFAs using a heterogeneous acid catalyst. There are three HCRs units, and each HCR composed of a 3D-printed rotor and stator, is separated by flanges and equipped with a basket for holding Amberlyst-15 catalyst. Through response surface methodology (RSM), the esterification process is optimized by adjusting its optimal parameters, namely, methanol (2–12 wt%), circulation time (30–170 min), and rotor speed (1000–3000 rpm). The optimal conditions for achieving a maximum methyl ester purity of 89.76 wt% in converting FFA in first-step esterified oil are 9 wt% methanol (molar ratio of methanol to oil of 4:1), 133 min of circulation time, and 2000 rpm of rotor speed. An 82.48 wt% biodiesel yield is achieved from the HCRs in series under the optimal conditions. Scanning electron microscope images reveal that after the esterification process, there are minor cracks and defects on the catalyst’s resin surface, indicating the presence of residual reactants. Further examination of the catalyst after the esterification process, reveals an average absorption pore diameter of 341.41 Å and BET surface area of approximately 41.68 m2/g. Although there were slight physical changes in the catalyst, HCRs technology offers a viable FFA reduction process that could enhance biodiesel production efficiency. Moreover, the optimized conditions achieved in this study contribute to the advancement of biodiesel production processes and provide insights into the performance of the catalyst used.

An Effective Synthesis of Phosphated Silica (PO<sub>4</sub>/SiO<sub>2</sub>) Catalyst and its Performance for Converting Ethanol into Diethyl Ether (DEE)

Research on phosphated silica (PO4/SiO2) as a heterogeneous acid catalyst in the dehydration reaction of ethanol into diethyl ether has been carried out. The PO4/SiO2 was prepared from TEOS by a wet impregnation method with various concentrations of H3PO4 (1, 2, 3, 4 M) and calcination temperatures (400, 500, and 600 °C) to obtain it with an optimum acidity. Afterward, the catalysts were characterized by FTIR, XRD, SEM-EDX, SAA, and TG-DTA. Ethanol dehydration was run using a fixed-batch reactor with a flow of N2 gas, and GC determined the selectivity of diethyl ether. The PS-4-400 catalyst had the highest activity and selectivity in the ethanol dehydration to diethyl ether at a temperature of 225 °C, with a conversion of 58.00% and a DEE selectivity of 3.71%.

Halloysite Nanotube Modified (CuO@HNTs-SO3H) Novel Heterogeneous Catalyst for One-Pot Synthesis of Tetrahydrobenzo[ɑ]Xanthen-11-One

In this study, CuO@HNTs-SO3H was investigated as a novel eco-friendly heterogeneous solid acid catalyst prepared by straightforward co-precipitation method. Thus, the cost-effective CuO NPs was used to modify halloysite nanotubes initially, which were subsequently further functionalized with sulfonic acid. The prepared catalyst was analyzed by means of FT-IR, XRD, EDX, SEM and TGA methods. Its catalytic activity is investigated in the solvent-free one-pot condensation of various aromatic aldehydes, dimedone, and β-naphthol to produce tetrahydrobenzo[a]xanthen-11-one derivatives. A few benefits of the discovered method are its simple process, quick reaction time, high yields (96%), affordable cost, and the catalyst ability to be reused without losing its activity.

Selective synthesis of oxygenated fuel derivative from microwave assisted acetalization of glycerol: Optimization and mechanistic investigations

Glycerol contains 52 wt% oxygen content, therefore unable to be directly used as fuel due to its poor combustion ability. Thus, the catalytic conversion of glycerol into various oxygen-containing fuel additives is grabbing more attention nowadays. This work provides a novel, sustainable, and eco-friendly method for synthesizing heterogeneous acid carbon catalysts from pearl millet cob (PMC) waste. The hydrothermal carbonization process was carried out at different temperatures to fabricate the series of sulfonated pearl millet cob (SPMC) catalysts. XRD, FT-IR, SEM-EDS, XPS, BET, TGA, and CHNSO analyses were performed to characterize fabricated catalysts. The synthesized catalyst, SPMC-70 (catalyst synthesized at 70 °C temperature), possesses OH, COOH, and SO3H functional groups and a significant total acid density (2.03 mmol/g) with 37 m2/g surface area. The SPMC catalysts were employed for the microwave-assisted acetalization reaction of glycerol with acetone for solketal production. The optimization process was carried out using various reaction parameters, including catalyst dosage (2–6 wt.%), reaction temperature (30–60 °C), glycerol to acetone (GL to AC) molar ratio (1:3–1:9), and reaction time (4–13 min). The SPMC-70 catalyst showed the highest catalytic activity among all the synthesized catalysts and provided 99.11 ± 0.3 % GL conversion with 100 % selectivity of solketal under optimal reaction conditions. Additionally, the recyclability test was performed, and it found that the best catalyst was reusable for up to five reaction cycles. These results showed the effectiveness of carbon-based heterogeneous acid catalysts in deriving a fuel additive, solketal.

Microwave and ultrasound-assisted green protocols for 5-methylthiazole induced Betti bases: molecular docking, in-silico pharmacokinetics, and anticancer activity studies

ABSTRACT Herein, we describe an efficient one-pot three-component microwave and ultrasound-endorsed approaches for synthesizing distinct 5-methylthiazole induced Betti bases (5-methyl-thiazol-2-ylamino-aryl-benzylnapthols) employing silica sulfuric acid (SSA, silica-OSO3H) as an active heterogeneous acid catalyst. The title compounds produced in good yields (86–95%) from naphthalen-2-ol, 5-methylthiazol-2-amine, and assorted aryl aldehydes; and structurally characterized by spectral and elemental analyses. A comprehensive comparative study of conventional, ultrasonic, and microwave-irradiated synthetic routes has been achieved by optimizing various reaction parameters. These new protocols provide several advantages, including the use of an inexpensive, non-toxic, and reusable catalyst. Additionally, they benefit from mild reaction conditions, short reaction times, and simple workup and purification procedures, thereby increasing their practicality. Furthermore, the synthesized compounds were evaluated for their anticancer potency against A-549 (lung cancer) and A-498 (kidney cancer) cell lines, with scaffold IVa demonstrating excellent (GI50 < 10 µg/mL) inhibitory activity against A-549. Additionally, molecular docking was performed to investigate potential binding interactions between ligands and proteins. Scaffold IVa exhibited the best docking with cancerous target proteins 1M17 (−8.9 kcal/mol) and 1M14 (−7.2 kcal/mol), thereby supporting our bio-activity studies.

Sulfonated carbon–based heterogeneous acid catalysts in direct biomass redox flow fuel cell: A review

AbstractThis review focused on the potential applications of sulfonated carbon–based heterogeneous acid catalysts for the hydrolysis of lignocellulosic biomass (LCB) fuel feedstock and the development of membrane electrode assembly (MEA) for the direct biomass redox flow fuel cell (DBRFFC). LCBs are hydrolysed to yield simple sugars, which are subsequently oxidized over catalysts in the anode tank of the DBRFFC to generate electricity. Ferric chloride used as a catalyst in the DBRFFC is not efficient for glucose production from LCB, such that the power performance of the DBRFFC is affected during glucose oxidation due to low glucose yield from LCB for electron generation. Sulfonated carbon–based solid acid catalysts (SCSACs) have been established as efficient catalysts for the hydrolysis of LCB and as metal catalyst supports for the fabrication of MEA for further oxidation of glucose and its oxidation by‐products. These capabilities of SCSACs can be explored and applied to significantly improve the power output of the DBRFFC through efficient hybrid catalyst design. There is still a scarcity of literature on this subject and their combination with ferric chloride to enhance glucose yield and oxidation in DBRFFC. This gap was filled by discussing the various types of sulfonated carbon–based catalysts, highlighting their synthesis routes, and their applications in organic compound synthesis, and membrane electrode development in DBRFFC. The knowledge derived will certainly be beneficial to researchers willing to improve the performance of DBRFFC through molecular catalyst design and electrode membrane development for application in DBRFFC.

Post-Synthetic Modification of a 1D Mixed-Linker Zn(II) Coordination Polymer for Acid-Catalyzed Alcoholysis of Epoxides.

Rational design of heterogeneous acid catalysts possessing uniform dispersion of active sites plays a significant role in the catalytic performance. In the present work, a coordination polymer, [Zn(4,4'-bpy)(μ-Hbtc)(H2O)] ⋅ 2H2O (Zn-CP), was solvothermally synthesized using 4,4'-bpy (=4,4'-bipyridine) and H3btc (=1,3,5-benzenetricarboxylic acid) mixed linkers. Single crystal X-ray analysis of the polymer displayed that Zn-CP chains were decorated with 4,4'-bpy having unidentate coordination fashion. Then, the free N atom of the linker in Zn-CP was functionalized by -SO3H groups to afford Zn-CP-SO3H with enhanced acidity. The structures were characterized by FT-IR, thermogravimetric analysis, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of NH3 (NH3-TPD), and field emission scanning electron microscopy (FE-SEM) analyses. The coordination polymer was employed as a heterogeneous catalyst for the alcoholysis of epoxides under room conditions. Zn-CP-SO3H exhibited excellent catalytic activity and regioselectivity in the methanolysis of styrene oxide within short reaction time.

Efficient and Sustainable Biodiesel Production via Transesterification: Catalysts and Operating Conditions

Biodiesel has received tremendous attention as a sustainable energy source. This review presents an overview of various catalysts utilized in biodiesel production and compares their potential for producing biodiesel. Presented here are the excellent features of the various catalysts while highlighting their drawbacks. For instance, production of biodiesel with homogeneous base catalysts is easy but it can only be used with refined oils having low levels of free fatty acid (FFAs). When homogeneous acid is used in esterification, it causes reactor corrosion. Water and FFAs do not affect heterogeneous acid catalysts. Thus, transesterification of triglycerides into biodiesel and converting FFAs into biodiesel through esterification can be catalyzed more efficiently using a heterogeneous acid catalyst. Biocatalysts are also being used to produce biodiesel from oils with high FFAs. However, heterogeneous acid catalysts and biocatalysts are not suitable for industrial application due to serious mass transfer limitations. Biodiesel yield and conversion were compared over various catalysts in this paper. Also presented are the effects of different reaction parameters on biodiesel yield over different catalysts. The correct interplay of factors like reaction temperature, time, alcohol-to-oil molar ratio, and catalyst loading produces optimal process conditions that give the highest biodiesel yield.

Solvent-free CO2 cycloaddition by one- and two-dimensional sodium coordination polymers based on hydrazonic ligands

We successfully synthesized and characterized four new coordination polymers of sodium: sodium 4-hydroxy-3-{[2-(pyridine-4-carbonyl)hydrazinylidene]methyl}benzene-1-sulfonate (NaL4-Py), sodium 3-[(2-benzoylhydrazinylidene)methyl]-4-hydroxybenzene-1-sulfonate (NaLPh), sodium 3-[(2-acetylhydrazinylidene)methyl]-4-hydroxybenzene-1-sulfonate (NaLMe), and sodium 3-[(2-carbamoylhydrazinylidene)methyl]-4-hydroxybenzene-1-sulfonate (NaLNH2). These polymers were synthesized through a 1:1 condensation reaction of hydrazide derivatives with sodium salicylaldehyde-5-sulfonate monohydrate (NaSalSO3) and were thoroughly characterized using various analytical techniques. The compounds NaLMe and NaLPh, crystallized in the P 1‾ and P21/n space groups, respectively, forming one-dimensional polymers. On the other hand, NaLNH2 and NaL4-Py crystallized in the Cmca and P 1‾ space groups, respectively, forming two-dimensional coordination polymers. The coordination environment of the sodium cation differed among the compounds, with the imine nitrogen atom interfering in NaL4-Py and NaLPh. The sulfonate group exhibited various coordination modes, resulting in the different dimensionalities of the polymers. Compounds NaL4-Py and NaLPh acted as heterogeneous Lewis acid catalysts for the solvent-free cycloaddition reaction of epichlorohydrine and CO2 into valued cyclic carbonate. High selective conversion (68 %) of epichlorohydrin to cyclic carbonate was obtained at mild conditions, 60 °C and 1 bar CO2, after 24 h of reaction.

Efficient biodiesel production by sulfonated carbon catalyst derived from waste glycerine pitch via single-step carbonisation and sulfonation

Glycerine pitch is a highly alkaline residue from the oleochemical industry that contains glycerol and contaminants, such as water, soap, salt and ash. In this study, acidic heterogeneous glycerol-based carbon catalysts were synthesised for biodiesel production via single-step partial carbonisation and sulfonation using pure glycerol and glycerine pitch, producing products labelled as SGC and SGPC, respectively. Carbon materials were obtained by heating glycerol and concentrated sulfuric acid (1:3) at 200℃ for 1 h. The produced SGC and SGPC displayed high densities of sulfonic group (–SO3H), i.e. 1.49 and 1.00 mmol·g−1, respectively, alongside carboxylic (–COOH) and phenolic (–OH) acid. In the catalytic evaluation, excellent oleic acid conversions of 96.0 ± 0.4 % and 92.4 ± 0.5 % were achieved using SGC and SGPC, respectively, under optimised reaction conditions: 1:10 M ratio of oleic acid to methanol, 5 % (w/w) catalyst, 64℃ and 5 h. SGPC was found to be recyclable with 68.5 % conversion after the 6th cycle, which was attributed to the loss of –SO3H and catalyst deactivation by the deposition of oleic acid on its surface. Remarkably, despite the impurities present in the glycerine pitch, the obtained results demonstrated that the reactivity of SGPC is comparable to SGC and superior to that of commercial solid acid catalysts, which demonstrated that the presence of impurities appears to have minimal impact on the production of carbon materials and their properties.

Sulfonated Graphene‐Based Materials as Heterogeneous Acid Catalysts for Solketal Synthesis by Acetalization of Glycerol

AbstractAcid catalysis plays a pivotal role in the industrial landscape due to its multifaceted contributions to various chemical processes in numerous sectors, including petrochemicals, polymers, food processing, and biodiesel production, among others. Sulfonated graphenes hold notable relevance as heterogeneous acid catalysts due to their unique combination of graphene's structural properties and the introduction of sulfonic groups as catalytic acid sites. Herein, we report the preparation of three sulfonated graphene‐based materials – sulfonated reduced graphene oxide (rGO‐SO3H), chlorosulfonated reduced graphene oxide (rGO‐HSO3Cl) and sulfonated graphene oxide (GO‐SO3H) – by different synthetic approaches. Physicochemical, textural, morphological, and acidic properties of all materials were characterized in detail by different instrumental techniques. Innovatively, these materials have been evaluated as heterogeneous acid catalysts in the solketal synthesis by acetalization of glycerol, which is considered an interesting building block to produce added‐value products. The density of acidic active sites and hydrophobicity were found to be conditioning parameters of the resulting catalytic activity in terms of conversion and selectivity. The best catalytic performance was obtained by rGO‐SO3H, reaching the maximum conversion towards solketal in 15 minutes under mild reaction conditions. The reusability and stability of all materials were also examined after three consecutive acetalization reactions with only a slight loss of catalytic activity.

Synthesis and E-metric Studies of an Economically Viable Heterogeneous Acid Catalyst for Production and Upscaling of Solketal

Synthesis and E-metric Studies of an Economically Viable Heterogeneous Acid Catalyst for Production and Upscaling of Solketal

Efficient production of biodiesel from palm fatty acid distillate using a novel hydrochar-based solid acid catalyst derived from palm leaf waste

To combat fuel shortages, pollution, and the exhaustion of natural oil resources, an environmentally friendly alternative to fossil fuels, such as biodiesel, is essential for meeting global transportation demands. A novel heterogeneous acid catalyst for production of biodiesel from low-cost, high free fatty acid feedstocks was synthesized in this study by activating and impregnating hydrochar from palm leaf (PL) waste with H3PO4 and H2SO4. Subsequently, the sulfonated catalyst was utilized for the esterification of palm fatty acid distillate (PFAD). FT-IR, XRD, FESEM, EDX, BET, TGA, and surface acidity methods were employed to characterize the acid catalyst. Using the one-variable-at-a-time (OVAT) technique, the optimized reaction conditions for esterification of PFAD using the hydrochar-based catalyst were 4 wt% catalyst loading, 353.15 K reaction temperature, 4 h reaction time, and 18:1 methanol: PFAD molar ratio. At these conditions, a maximum biodiesel yield of 93.56% was achieved. The catalyst exhibited excellent reusability and stability throughout five reaction cycles, maintaining biodiesel yields above 80% after each cycle. Analysis of the fuel properties revealed that the biodiesel derived from PFAD met the physiochemical criteria outlined in ASTM D6751, the American biodiesel standard. The kinetic study revealed that the esterification reaction followed pseudo-first-order kinetics with an activation energy (Ea) of 23.70 kJ/mol. Furthermore, the thermodynamic enthalpy (∆H*) and Gibbs' free energy (∆G*) of esterification were 20.9 and 33.41 kJ/mol, respectively, indicating that the reaction was an endothermic and non-spontaneous process.

Dicationic ionic liquid immobilized on polystyrene as an acidic, reusable, and efficient heterogeneous organocatalyst in organic transformations

Supported ionic liquids onto solid catalysts are among the most popular catalysts in chemical reactions with several unique advantages. However, the harsh reaction conditions, long reaction times, low product yields, and tedious work-up, are still the challenges for its application. A novel polystyrene-modified dicationic ion liquid [PS-(Im)2-SO3H] was synthesized through the reaction of chloromethyl polystyrene with imidazole, 1,4-dichlorobutane and 1,3-propanesultone. Its structure was characterized and confirmed using Fourier Transform Infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Dynamic Light Scattering (DLS), Scanning Electron Micrograph (SEM), Energy Dispersive Spectroscopy (EDS), and Elemental analyses. This polymer-supported dicationic ion liquid was used as an acidic heterogeneous catalyst for the synthesis of xanthene derivatives through condensation of aldehydes, dimedone, and β-naphthol. The products were obtained in high yields (88–97 %) at room temperature and short reaction time in ethanol as a green solvent. The reaction mixture was easily filtered to isolate the heterogeneous catalyst, which could be reused for at least eight cycles without any significant activity loss.

Comparison of Carbon-Based Heterogeneous Acid Catalyst from Water Hyacinth and Coconut Shell for Biofuel Production

Comparison of Carbon-Based Heterogeneous Acid Catalyst from Water Hyacinth and Coconut Shell for Biofuel Production

Synthesis and Application of Task-Specific Bimetal-Organic Frameworks in the Synthesis of Biological Active Spiro-Oxindoles.

The use of click chemistry as a smart and suitable method for the development of new heterogeneous catalysts is based on metal-organic frameworks as well as the production of organic compounds. The development of the click chemistry method can provide a new strategy to achieve superior properties of MOFs. Here, the two metals Co and Fe are used to create a bimetallic-organic framework. In the following, the click chemistry and postmodification method are well organized and an acidic heterogeneous porous catalyst is developed. This prepared catalyst was used as a highly efficient catalyst for the preparation of new spiro-oxindoles obtained through click chemistry with good to excellent yields (80-94%). This presented catalytic system can compete with the best reported catalytic systems. The findings showed that the presence of Co and Fe metals in the MOF, and the presence of the triazole ring on the catalyst, can increase the catalytic efficiencies. This study offers novel insights into the architecture of Metal-Organic Frameworks (MOFs), click chemistry, and biologically active compounds. Additionally, the research explores the antibacterial properties of the synthesized spiro-oxindoles and catalysts. The findings reveal significant antibacterial activities of the synthesized compounds against S. aureus, MRSA, and E. coli bacteria.

Construction of Indium(III)-Organic Framework Based on a Flexible Cyclotriphosphazene-Derived Hexacarboxylate as a Reusable Green Catalyst for the Synthesis of Bioactive Aza-Heterocycles.

The constant demand for eco-friendly methods of synthesizing complex organic compounds inspired researchers to design and develop modern, highly efficient heterogeneous catalytic systems. Herein, In-HCPCP metal-organic framework (SRMIST-1), a heterogeneous Lewis acid catalyst containing less toxic indium and eco-friendly robust cyclotriphosphazene and exhibiting notable chemical and thermal stability, durable catalytic activity, and exceptional reusability was produced through the reaction between indium(III) nitrate hydrate and hexakis(4-carboxylatophenoxy)-cyclotriphosphazene. In the SRMIST-1 structure, secondary building units {InO7} are assembled by a connection of η2- and η1-carboxylic oxo atoms from different HCPCP ligands, forming a three-dimensional network. The occurrence of regularly distributed In(III) sites in SRMIST-1 confers superior reactivity on the catalyst toward the synthesis of 2,3-dihydroquinazolin-4(1H)-ones and 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides by the cyclization reaction of 2-aminobenzamides and 2-aminobenzenesulphonamides with aldehydes under optimized reaction conditions, respectively. The notable features of this method include broad functional group compatibility, low catalyst loading (1-5 mol %), mild reaction conditions, easy workup procedures, good to excellent reaction yields, ethanol as a green solvent, reusability of the catalyst (five cycles), and economic attractiveness, which is mainly due to sustainability of SRMIST-1 as a reusable green catalyst. Our findings demonstrate that the highly reactive and reusable green catalyst finds widespread applications in medicinal chemistry.