Solvent-free Reaction Conditions Research Articles

Bifunctionality of amine-modified metal-organic frameworks for CO2 capture and selective utilization in cycloaddition

In this study, copper- and chromium-based (HKUST-1 and MIL-101(Cr), respectively) metal-organic frameworks (MOF) functionalized with amine groups (HKUST-1‒NH2 and MIL-101(Cr)‒NH2, respectively) were directly synthesized using 2-aminoterephthalic acid as an organic linker via hydrothermal method without adding hydrofluoric acid. They were then investigated for their potential applications in dynamic carbon dioxide (CO2) adsorption and conversion of epoxides with CO2. The functionalized MOF (HKUST-1‒NH2 and MIL-101(Cr)‒NH2) retained their desired textural properties, while gaining a significantly enhanced Lewis basic character for CO2 capture and catalysis application. Both HKUST-1‒NH2 and MIL-101(Cr)‒NH2 not only showed an improved CO2 uptake capability, but also an excellent and stable regenerability over multiple adsorption-desorption cycles. MIL-101(Cr)‒NH2 exhibited a higher performance than the parent MOF and HKUST-1‒NH2 in the transformation of styrene oxide (SO) with CO2 to styrene carbonate (SC) and carbonate oligomers (COL) due to combined effect of its textural properties and basicity. Under solvent-free system, COL from monomeric SC was directly obtained, up to 72.4 % yield, via in situ oligomerization. Optimization of the solvent-free reaction conditions was carried out to control the selective pathway of CO2 utilization between cycloaddition and oligomerization. In the presence of acetonitrile, a > 97 % yield of SC was achieved over MIL-101(Cr)‒NH2 under a mild reaction condition (120 °C and 20 bar of CO2). Reaction mechanisms for the cycloaddition and oligomerization of SO with CO2 are also proposed to comprehend the role of MOF, amine group, and co-catalyst. The combined efficient CO2 adsorption and capability to produce CC and COL makes the synthesized MOF promising materials for CO2 capture and selective utilization.

Synthesis and characterization of bagasse cellulose-based quaternary ammonium peroxyphosphotungstate and their catalytic properties for cyclohexene oxidation in the absence of any solvent

Bagasse cellulose, an industrial waste byproduct of sugar production, was demonstrated to be a viable solid support for a solid-phase ionic oxidation catalyst enabling organic solvent-free aqueous reaction conditions and facile catalyst recovery. Bagasse cellulose-supported quaternary ammonium peroxyphosphotungstate was synthesized from bagasse cellulose-supported quaternary ammonium chloride, phosphotungstic acid, and hydrogen peroxide. The chemical structure of this material was characterized by SEM, XRD, FT-IR, XPS, and 13C NMR, revealing stability of the cellulose matrix to the catalyst loading conditions and effective dispersion of the acicular catalyst crystals throughout the matrix. High catalytic activity of this synthetic complex was demonstrated in the oxidation of cyclohexene to 1,2-cyclohexanediol with hydrogen peroxide in the absence of solvent. Optimized conditions providing trans-1,2-cyclohexanediol with 86.2 % selectivity were 12 wt% catalyst and 4 mL/g 30 % H2O2 (vs. cyclohexene) at 50 °C for 10 h.

Optimization of biotransformation process for the synthesis of pyrazine-2-carboxylic acid hydrazide using acyltransferase activity of Bacillus smithii IITR6b2 in batch and fed-batch mode

The synthesis of pyrazine-2-carboxylic acid hydrazide, a heterocyclic hydrazide compound, with negligible production of the by-product (pyrazine-2-carboxylic acid) in a solvent-free reaction condition was developed using the acyltransferase activity of amidase of Bacillus smithii strain IITR6b2. This study involves a greener approach with no hazardous chemicals and one-step biotransformation of pyrazinamide to its acid hydrazide (through hydrazinolysis). The Central Composite Design of the Response Surface Methodology was used to find the factors affecting the synthesis of the pyrazine-2-carboxylic acid hydrazide and pyrazine-2-carboxylic acid to find its true optimum. The four factors, namely pyrazinamide, hydrazine dihydrochloride, temperature, and cell concentrations, were considered during optimization. The optimized reaction conditions from the Central Composite Design for achieving the 32.26 mM of pyrazine-2-carboxylic acid hydrazide involve 40 mM of pyrazinamide, 1000 mM of hydrazine dihydrochloride with 2.5 mg/mL cell concentration at 20 °C. It resulted in an optimum production of pyrazine-2-carboxylic acid hydrazide utilizing the acyltransferase activity of amidase of Bacillus smithii IITR6b2, and the results obtained through the Design of Experiments were validated. The fed-batch biotransformation was carried out with alginate-entrapped whole-cell enzyme with the following parameters: agitation at 200 rpm, a pyrazinamide concentration of 40 mM, and 1000 mM of hydrazine dihydrochloride. The final pyrazine-2-carboxylic acid hydrazide concentration of 126 mM was obtained, corresponding to a 63% molar conversion.

Amphiphilic Catalysts Comprising Phosphomolybdic Acid Fastened on MIL-101(Cr): Enabling Efficient Oxidative Desulfurization under Solvent-Free and Moderate Reaction Conditions

Amphiphilic Catalysts Comprising Phosphomolybdic Acid Fastened on MIL-101(Cr): Enabling Efficient Oxidative Desulfurization under Solvent-Free and Moderate Reaction Conditions

Coupled conversion of polyethylene and carbon dioxide catalyzed by a zeolite-metal oxide system.

Zeolite-catalyzed polyethylene (PE) aromatization achieves reduction of the aromatic yield via hydrogenation and hydrogenolysis reactions. The hydrogen required for CO2 hydrogenation can be provided by H radicals formed during aromatization. In this study, we efficiently convert PE and CO2 into aromatics and CO using a zeolite-metal oxide catalyst (HZSM-5 + CuZnZrOx) at 380°C and under hydrogen- and solvent-free reaction conditions. Hydrogen, derived from the aromatization of PE over HZSM-5, diffuses through the Brønsted acidic sites of the zeolite to the adjacent CuZnZrOx, where it is captured in situ by CO2 to produce bicarbonate and further hydrogenated to CO. This favors aromatization while inhibiting hydrogenation and secondary hydrogenolysis reactions. An aromatic yield of 62.5 wt % is achieved, of which 60% consisted of benzene, toluene, and xylene (BTX). The conversion of CO2 reaches values as high as 0.55 mmol gPE-1. This aromatization-hydrogen capture pathway provides a feasible scheme for the comprehensive utilization of waste plastics and CO2.

An efficient and concise method to 2-methylmycoleptodiscin A from (−)-sclareol

Natural product analogue 2-methylmycoleptodiscin A has been simply synthesized from commercially available (−)-sclareol in 36 % overall yield. The crucial step was the intramolecular Friedel − Crafts reaction at C-4 of the indole ring using optimized catalyst Eaton's reagent under benign and solvent free reaction conditions.

Solvent-free strategy for facile synthesis and cytotoxicity evaluation of benzimidazole derivatives

This study reports a facile synthesis and the cytotoxic evaluation of N–H benzimidazoles. This synthetic method made use of the condensation reaction between o-phenylenediamine and benzylamine and was highlighted by its solvent-free reaction conditions and short reaction time with the use of Na2S2O5 as an inexpensive and environmentally friendly oxidizing agent. The cytotoxicity assays revealed that the benzimidazole derivatives 3l, 3h, and 3r displayed strong activity against the HeLa cancer cell line with the IC50 of 1.54 μM, 0.86 μM, and 1.03 μM, respectively, which were 5.6-fold, 10-fold, and 8-fold stronger than the positive control 5-fluorouracil (5-FU, IC50 = 8.61 μM). Furthermore, both compounds 3h and 3r exhibited similar cytotoxicities against MCF-7, which were equivalent to that of 5-FU and about 2.5-fold stronger than 5-FU towards the A549 cell line.

Preparation of 4,4-bis(5-methylthiophen-2-yl)pentanoic acid from biomass-based functional molecules using solid acid catalysts

For the first time, the successful synthesis of 4,4-bis(5-methylthiophen-2-yl)pentanoic acid (bisthiophenic acid-methyl; BTA-M) and its alkyl esters (BTAE-M) from levulinic acid (LA) and its esters with 2-Methylthiophene (2-Met) has been achieved, utilizing solid acid catalysts (Amberlyst-15 and Indion-190). Notably, Indion-190, a cost-effective catalyst, demonstrated the formation of BTA-M and bisthiophenic methyl ester-methyl (BTME-M) with 96–98% selectivities and 99% conversion of LA and methyl levulinate under optimized, solvent-free reaction conditions. The recyclability of Indion-190 has been showcased, maintaining good recyclability for the preparation of BTA-M and BTME-M over three reaction cycles, with a slight decrease in the conversion of reactants.

Green synthesis of 1,3-Thiazolidin-4-ones derivatives by using acid-activated montmorillonite as catalyst

An environmentally friendly, clean, and applicable methodology for synthesizing 1,3-Thiazolidin-4-one derivatives was developed. This method produced the target compounds in high yields and short reaction times by using solvent-free reaction conditions with heterogeneous catalysts, montmorillonite (MT) and acid-activated montmorillonite (acid-MT). MT and acid-MT were investigated in the synthesis using a variety of techniques, including conventional heat, ultrasonic, and microwave irradiation, with the investigation of two types of factors, namely time and temperature. X-ray diffraction, N2 adsorption–desorption, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to characterize the MT and acid-MT catalysts. FTIR, 1H NMR, 13C NMR, and mass spectra were used to characterize each product. The ring-cyclization step, with its short time and high yield percentage, is the most important factor for the strength of the prepared catalyst, acid-MT. Additionally, the acid-MT catalyst was easily recoverable and can be reused up to five times without suffering a substantial reduction in catalytic activity.

Turning waste into resources. Efficient synthesis of biopolyurethanes from used cooking oils and CO2

The coupling reaction of carbon dioxide and highly-substituted epoxides derived from renewable resources such as fatty acids and waste vegetable oils (cooking oils derived from olive and sunflower) leads to the synthesis of new bio-derived cyclic carbonates using efficient metal-free bifunctional organocatalysts under mild and solvent-free reaction conditions. Once cyclic carbonates derived from biobased sources were synthesized, the design of non-isocyanate polyurethanes (NIPUs) with different chemical structures was investigated by their reaction with a broad substrate scope of diamines. The NIPUs materials were characterized by spectroscopic techniques (NMR and IR) and their molecular weights and polydispersities were determined by GPC studies. Finally, thermal properties of the polymers were studied by DSC and TGA analyses.

CuI Coordination Polymer‐Catalyzed Azide–Alkyne Cycloaddition Click Reaction at Room Temperature

AbstractFramework based compounds for eco‐friendly catalysis is of utmost industrial interest. CuI‐catalyzed “click” reactions are a class of highly efficient and widely used chemical reactions in organic synthesis for potential applications in biotechnology, medicine, polymer, and material sciences. The importance of click chemistry also acknowledge by 2022 Noble Prize in chemistry. One of the most well‐known click reactions is the copper‐catalyzed azide‐alkyne cycloaddition (CuAAC), which is a type of Huisgen 1,3‐dipolar cycloaddition reaction. Herein, three stable copper(I)‐coordination polymers (CPs), [Cu(4‐ABPT)Cl], CP‐1; [Cu(4‐ABPT)Br], CP‐2; [Cu2(4‐ABPT)0.5I2], CP‐3; (4‐ABPT=3,5‐di(pyridine‐4‐yl)‐4H‐1,2,4‐triazol‐4‐amine) have been chosen for CuAAC reaction, due to presence of both Lewis acidic (copper ion), and basic (pyridyl and amine) sites. The counter anion plays a crucial role in their structural motif as well as catalytic efficiency. These easily synthesizable and scalable catalysts exhibit the trend of CP‐1>CP‐2>CP‐3 in catalysis for the selective conversion of phenylacetylene, benzyl bromide, and sodium azide into 1,4‐cycloaddition product within 2 h at ambient temperature and solvent free reaction conditions. CuAAC reaction using catalyst CP‐1 exhibits near quantitative conversion within 2 h at room temperature in solvent free conditions. Herein, we demonstrated the bulk‐scale synthesis of CuI CPs for efficient azide‐alkyne cycloaddition click reaction under mild reaction conditions.

Covalent immobilization of POM-based ILs on magnetic graphene oxide for efficient catalytic oxidative desulfurization of model fuel under solvent-free and moderate reaction conditions

A series of divanado-substituted phosphomolybdic acid-based ionic liquids was successfully prepared and immobilized on the surface of a magnetic graphene oxide (APTES-mGO). The prepared catalysts were characterized and used in oxidative desulfurization (CODS) of model fuel in a solvent-free system. The sample of [C12mim]5PV2Mo10/APTES-mGO, with an alkyl length chain of C12, showed the highest DBT removal percentage, which helped to form a stable Pickering emulsion system. Moreover, the effect of operating conditions, including the reaction time and temperature, catalyst dosage, and O/S molar ratio, on the DBT removal efficiency of the catalyst were investigated employing response surface methodology (RSM). The results showed that the [C12mim]5PV2Mo10/ APTES-mGO was able to completely desulfurize the model fuel under the optimized conditions of 4 g catalyst per liter of the fuel, T = 45 °C, t = 30 min, and O/S = 4. The CODS performance of the catalyst in the presence of other refractory sulfur components (BT and 4,6-DMDBT) was also studied. The designed catalyst could be recovered 8 times without significant losing of its catalytic activity. In addition, 87.15% sulfur removal was achieved for an untreated real diesel sample by adding an extraction step after the CODS processes.

A bio-waste derived sustainable heterogenous catalyst for Biginelli reaction

This study is targeted at agricultural waste-derived heterogeneous catalysts, which have been effectively employed for Biginelli reaction. The application of cotton waste (Gossypium) derived lignin as a heterogeneous catalyst for C–C bond formation via one pot multicomponent Biginelli reaction. Here we hypothesize that the preparation of bio-waste derived catalyst by high temperature pyrolysis method under anaerobic conditions. The bio-waste derived heterogeneous catalyst (BDC) was well characterized by using different analytical techniques such as BET, SEM, TEM, XRD, DSC, TGA, ICP. The acidity of the catalyst was determined by a Hammett indicator test and titration method. An excellent yield of 6-methyl-2-oxo/thio-4-phenyl substituted-1,2,3,4-tetrahydropyrimidine-5-ethyl carboxylate derivatives was obtained in shorter reaction time (>80% yield in 15–30 min). The catalyst used in these studies has the advantage of being a waste material. Consequently, it is a low-cost, easily prepared, recyclable and environmentally benign. In addition, the use of a biogenic renewable catalyst, its atom economy, and room temperature and solvent-free reaction conditions and the avoidance of column chromatography make the protocol highly significant from green and sustainable chemistry perspectives. The synthesized compounds were characterized by modern analytical techniques like NMR, MS, FT-IR, CHNS analysis. The experimental parameters like % mole of catalyst, mole ratio, temperature and time for reaction completion were also optimized to achieve maximum yield and purity. The surface interaction between BDC and reactant was also studied.

A sustainable avenue for the synthesis of propargylamines and benzofurans using a Cu-functionalized MIL-101(Cr) as a reusable heterogeneous catalyst

A heterogeneous copper-catalyzed A3 coupling reaction of aldehydes, amines, and alkynes for the synthesis of propargylamines and benzofurans has been developed. Here, the modified metal–organic framework MIL-101(Cr)-SB-Cu complex was chosen as the heterogeneous copper catalyst and prepared via post-synthetic modification of amino-functionalized MIL-101(Cr). The structure, morphology, thermal stability, and copper content of the catalyst were determined by FT-IR, PXRD, SEM, TEM, EDX, TGA, XPS, and ICP-OES. The catalyst shows high catalytic activity for the aforementioned reactions under solvent-free reaction conditions. High yields, low catalyst loading, easy catalyst recovery and reusability with not much shrink in catalytic activity, and a good yield of 82% in gram-scale synthesis are some of the benefits of this protocol that drove it towards sustainability.

Synthesis of 1, 8-Naphthyridine-3-Carbonitriles under solvent-free conditions using ceric ammonium nitrate

1,8-naphthyridines are synthesized using a four-component, one-pot approach. This method includes the reaction of aromatic aldehyde, malononitrile, 1,6-dimethylpyridin-2(1H)-one, substituted aniline in a solvent-free condition catalyzed by Ceric Ammonium Nitrate (CAN). Contrary to the reported literature, this distinct method houses several promising factors to the same degree as solvent-free reaction conditions, shorter reaction duration, excellent yields, and a straightforward extraction process.

Nitrogen-Enriched Biguanidine-Functionalized Cobalt Ferrite Nanoparticles as a Heterogeneous Base Catalyst for Knoevenagel Condensation under Solvent-Free Conditions.

Designing efficient, economical heterogeneous catalysts for the Knoevenagel condensation reaction is highly significant owing to the importance of reaction products in industries as well as pharmaceutics. Herein, we have designed and synthesized biguanidine-functionalized basic magnetically retrievable cobalt ferrite nanoparticles (CFNPs) for the synthesis of Knoevenagel condensation products using benzaldehydes and active methylene compounds (malononitrile/ethyl cyanoacetate/cyanoacetamide). Several advanced techniques, such as Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibration sample magnetometry (VSM), were utilized to precisely characterize the catalyst. The robust features of the current approach involve outstanding catalytic performance, solvent-free reaction conditions, ease of catalyst retrievability, easy workup procedure, large substrate tolerance, high turnover frequency (TOF) values (up to 486.88 h-1), values of green chemistry metrics such as E-factor (0.15), reaction mass efficiency (RME) value (87.07%), carbon efficiency (93.4%), and atom economy (AE) value (88.10%) close to their ideal values, and recyclability up to eight runs without a considerable reduction in activity, boosting the appeal of this approach from a commercial and ecological point of view.

Novel anthraquinone α-aryl-α-aminophosphonates: Synthesis, spectroscopy and imaging by confocal laser scanning microscopy of trematode Opisthioglyphe ranae

A small library of new anthraquinone α-aryl-α-aminophosphonates with N-C-P molecular fragment was synthesized under Kabachnik-Fields one-pot solvent-free reaction conditions from 1-aminoanthraquinone. 1H-, 13C-, 31P NMR and FTIR spectroscopy and high-resolution accurate mass measurement was employed to confirm structures of new dyes. The photophysical parameters of the studied α-aminophosphonates have been investigated by means of UV–Vis and fluorescence spectroscopy in organic solvents of varying polarity. Obtained compounds were found to emit light from 586 nm (EtOAc) to 620 nm (DMSO) with fluorescence bathochromic shifts reaching up to 30 nm, Stokes shift of 4573 cm– 1 and photostability of up to 60 % of initial intensity upon photofading for 4 h. α-Aryl-α-aminophosphonate was used for the first time as a dye for rapid bioimaging of trematode Opisthioglyphe ranae in confocal laser scanning microscopy.

Trimetallic Oxide Foam as an Efficient Catalyst for Fixation of CO2 into Oxazolidinone: An Experimental and Theoretical Approach

The excess anthropogenic CO2 depletion via the catalytic approach to produce valuable chemicals is an industrially challenging, demanding, and encouraging strategy for CO2 fixation. Herein, we demonstrate a selective one-pot strategy for CO2 fixation into "oxazolidinone" by employing stable porous trimetallic oxide foam (PTOF) as a new catalyst. The PTOF catalyst was synthesized by a solution combustion method using transition metals Cu, Co, and Ni and systematically characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), N2 sorption, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) analysis. Due to the distinctive synthesis method and unique combination of metal oxides and their percentage, the PTOF catalyst displayed highly interconnected porous channels along with uniformly distributed active sites on its surface. Well ahead, the PTOF catalyst was screened for the fixation of CO2 into oxazolidinone. The screened and optimized reaction parameters revealed that the PTOF catalyst showed highly efficient and selective activity with 100% conversion of aniline along with 96% selectivity and yield toward the oxazolidinone product at mild and solvent-free reaction conditions. The superiority of the catalytic performance could be due to the presence of surface active sites and acid-base cooperative synergistic properties of the mixed metal oxides. A doubly synergistic plausible reaction mechanism was proposed for the oxazolidinone synthesis experimentally with the support of DFT calculations along with bond lengths, bond angles, and binding energies. In addition, stepwise intermediate formations with the free energy profile were also proposed. Also, the PTOF catalyst displayed good tolerance toward substituted aromatic amines and terminal epoxides for the fixation of CO2 into oxazolidinones. Very interestingly, the PTOF catalyst could be significantly reused for up to 15 consecutive cycles with stable activity and retention in physicochemical properties.

Green halogenation of aromatic compounds using environmentally friendly synthesized rod-like metal-organic framework (MIL-88A) catalyst

Metal-organic frameworks (MOFs) have been extensively investigated as catalysts to synthesis of various chemical and eliminate toxic pollutants in water. Herein, MOF was used as an efficient catalyst for the halogenation of aromatic materials (aniline, b-naphthol, and naphthalene). The rod-like MIL-88A as an iron-based MOF was synthesized using Fe3+ with fumaric acid in water as a green solvent. The synthesized catalyst was characterized by FT-IR, XRD, SEM, and Raman. The rod-like MIL-88A is evaluated as the heterogeneous catalyst to activate KBr/I for the halogenation of aromatic compounds. 1HNMR and 13CNMR were used to characterize the halogenated aromatic materials. Halogenation of aromatic rings has been studied using potassium bromide (KBr) and potassium iodide (KI) as brominating and iodinating agents in the presence of rod-like MIL-88A as oxidant under solvent-free reaction (grinding) conditions. The halogenation yield of aromatics materials was 80–99%. The conversion yield of aniline to 4‑bromo aniline using 0, 10, 20, 30, 40, and 50 mg of rod-like MIL-88A at 25 min and room temperature (25 ºC) were 0%, 76%, 85%, 90%, 95%, and 88%, respectively. In addition, the conversion yield of B-naphthol to 1-Bromo-2-naphthol using a green catalyst was 97%. Also, the conversion yield of Naphthalene to 1-Bromonaphthalene using a rod-like catalyst. In most cases, mono-halogen derivatives were obtained in good yield without the aid of strong acids. In addition, the rod-like MIL-88A catalyst shows excellent stability and can be reused after proper washing treatments. It could be concluded that green synthesized rod-like MIL-88A could be used as an environmentally friendly catalyst for the halogenation of aromatics via grinding as a solvent-free reaction at room temperature.

Carbon-Supported Nickel Catalysts—Comparison in Alpha-Pinene Oxidation Activity

In this work, carbon-supported nickel catalysts with different Ni content (1, 2.5, 5, 10, and 20 wt%) were tested in the oxidation of alpha-pinene in solvent-free reaction conditions. The process of catalyst preparation consisted of two stages. In the first stage, the activated carbon from spent coffee grounds was obtained. In the second stage, the active phase in the form of nickel compounds was applied using two methods: (1) the impregnation of the material with the nickel salt solution, and next reduction in H2, and (2) the hydrothermal method in the autoclave using the reductor and the reaction stabilizer. The obtained catalysts were subjected to the following instrumental studies: FT-IR, XRD, SEM, and N2 adsorption at −196 °C. The performed catalytic tests showed that the catalysts containing 5 wt% of Ni (porous material obtained by the impregnation method) and 1 wt% of Ni (porous material obtained by the hydrothermal method) were the most active in the oxidation of alpha-pinene, and the main oxidation products were alpha-pinene oxide, verbenol, and verbenone. Ultimately, the hydrothermal method of catalyst preparation turned out to be more advantageous because it allows one to obtain higher selectivities of the epoxide compound, probably due to the greater stability of this organic compound in pores.