Organic Solvent-free Conditions Research Articles

Synthesis, characterization, and antibacterial activity of novel bis(indolyl)methanes sourced from biorenewable furfurals using gluconic acid aqueous solution (GAAS) as a sustainable catalyst.

Bis(indolyl)methanes (BIMs) are important heterocycle-containing molecular scaffolds that show remarkable biological and pharmacological activities. This work reports the synthesis of novel BIMs using carbohydrate-derived 5-substituted-2-furaldehydes as renewable reactants. Structural diversity was introduced in the BIMs as substituents in the indole and furaldehyde moieties. Various commonly encountered biorenewable carboxylic acids were screened as catalysts for the acid-catalyzed transformation under organic solvent-free conditions. All the novel BIMs were characterized by spectroscopic techniques (FTIR, 1H-NMR, 13C-NMR) and elemental analysis. The reaction was optimized on the reaction temperature, duration, catalyst type, and catalyst loading. The gluconic acid aqueous solution (GAAS) showed the best catalytic activity for the transformation, affording satisfactory isolated yields (68-96%) of the targeted BIMs under optimized conditions. The GAAS catalyst was conveniently recovered from the reaction mixture and reused for four consecutive cycles without catastrophic loss in either mass or activity. Moreover, the antibacterial activities of the novel BIMs were studied on Gram-positive and Gram-negative bacterial strains, such as Enterococcus faecalis and Pseudomonas syringae.

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.

K2CO3/TBAB, a Composite of Inorganic and Organic Salts, a Novel and Powerful Media for Regioselective Michael Addition of Dihydropyrimidinones to Acrylic Esters Under and Without Solvent Conditions

Aims: Synthesis of dihydropyrimidinones derivatives. Background: carrying out reactions in the green route and organic solvent-free conditions. Objective: Regioselective Michael addition of dihydropyrimidinones to acrylic esters. Methods: The reaction proceeded in the presence of K2CO3/TBAB, a media of inorganic base K2CO3 and organic ionic salt TBAB (tetrabutylammonium bromide) at 100oC. Results: A series of new dihydropyrimidinone derivatives using aza-Michael addition reaction were synthesized under solvent-free conditions. Conclusion: The reaction is characterized by high efficiency, relatively short reaction time, high yields, simple environmentally friendly reaction conditions. Other: The reaction of acrylic esters with dihydropyrimidinones produced N3-substituted derivative of dihydropyrimidinones with 85-95% yields in 6 h.

Tamarindus indica seed ash extract for C-C coupling under added organics and volatile organic solvent-free conditions: a waste repurposing technique for Suzuki-Miyaura reaction.

A tremendous research has been appeared on Pd-catalyzed Suzuki-Miyaura cross-coupling (SMC) during the last four decades due to its high prominence in constructing biaryl motifs of several complexes as well as simple organic compounds of high biological and commercial significance. The use of organic solid waste-derived materials for SMC in benign solvents like water/aqueous media is a very good achievement in these cases. We report in this article the usability of water extract of Tamarindus indica seeds ash (WETS) as a renewable base and reaction medium for Pd(OAc)2-catalyzed SMC reaction at room temperature (RT). The WETS has been characterized using powder XRD, EDAX, SEM, and FTIR analysis. Furthermore, this process is highly environmentally beneficial by the waste repurposing to prominent chemical transformation along with the advantages such as ambient condition and avoids non-renewable chemicals like volatile organic solvents, ligands, promoters, and bases. Based on these merits and the quick reactions with high yields of products, this method can attain the interest of the scientific community in exploring the waste-derived ashes to significant chemical transformations. Tamarindus indica seed ash extract for C-C coupling under added organics and volatile organic solvent-free conditions: a waste repurposing technique for Suzuki-Miyaura reaction.

Highly economic and waste valorization strategy for multicomponent and Knoevenagel reactions using water extract of tamarind seed ash.

The application of solid organic waste-originated products in the preparation of synthetically and biologically significant compounds in aqueous media or pure water is a highly desired task in chemical synthesis that shows an effective solution to the circular economy and sustainable environment. In this article, we describe our research on the development of highly economic and sustainable protocols for the synthesis of biologically important oxygen-heterocycles (using a multicomponent reaction) and synthetically important olefins (via the Knoevenagel condensation reaction) using water extract of tamarind seed ash (WETS) as catalyst and aqueous reaction medium. The reactions are carried out at room temperature (RT) under toxic/problematic/volatile organic solvent-free conditions. Products of the current methods have been purified by using recrystallization technique. WETS was characterized from its FTIR, powder XRD, SEM, and EDAX data. Problematic and non-renewable solvents were avoided throughout the process from their synthesis to purification. The utilization of solid organic waste-originated catalyst and aqueous media, avoid of non-renewable substances as catalysts, media, separation solvents and promoters, and unobligating heating conditions can surely attract the attention of chemists towards exploring the waste-based products in chemical transformations.

Protein-friendly atom transfer radical polymerisation of glycerol(monomethacrylate) in buffer solution for the synthesis of a new class of polymer bioconjugates

A biologically friendly approach is proposed for the synthesis of biocompatible poly(glycerol monomethacrylate) (PGMA) in phosphate-buffer saline, through aqueous Activators ReGenerated by Electron Transfer for Atom Transfer Radical Polymerisation (ARGET ATRP) at ambient temperature, under organic-solvent free conditions which are well tolerated by active proteins. Controlled polymerisation of glycerol monomethacrylate (GMA) was successfully obtained, and this versatile technique was extended to the synthesis of active protein–PGMA conjugates, as PEG alternative for half-life extension of biotherapeutics. Lysozyme was tested as model protein for site-specific grafting-from polymerisations in phosphate buffer. Conjugated PGMA at relatively high degree of polymerisation (DP ≤ 250) preserved the enzymatic activity of lysozyme (up to 80%) and its stability (80% of retained activity) in serum and in trypsin solution. The combination of aqueous ARGET ATRP techniques and a grafting-from strategy may pave the way for a new generation of nanomedicines based on protein-PGMA conjugates.

Phase engineering in graphitic carbon nitride with imidazolium sulfonic acid chloride ionic liquid functionalization for photocatalytic side-chain oxidation of toluene

Herein, the phase and photocatalytic property of graphitic carbon nitride (g-C3N4) are modulated with the functionalization of ionic liquid (IL) by post-treatment of g-C3N4 with imidazolium sulfonic acid chloride. The structure, morphology and optoelectronic properties of synthesized catalyst were thoroughly investigated. The functionalization of Ionic liquid has induced polycrystallinity to the amorphous g-C3N4. The g-C3N4 –IL is highly efficient towards photocatalytic side-chain oxidation of toluene using H2O2with toluene conversion of 58% with 97% benzaldehyde selectivity in acetonitrile and toluene conversion of 49% and 96% benzaldehyde selectivity in organic solvent-free conditions. The synergy between g-C3N4 and the IL elevates the visible light absorption and lower photoluminescence intensity. The g-C3N4-IL catalyst efficiently halts over-oxidation to get high selectivity for the desired product. In addition, graphene oxide and reduced graphene oxide were also functionalized with IL to examine their photocatalytic efficiency and considerable efficiencies were observed. The g-C3N4-IL is highly stable and recyclable.

Synthesis, structure and catalytic activity of new oxovanadium(V) complexes with deferiprone and N,N-donor ligands

A pair of new water-soluble oxovanadium(V) complexes comprising of deferiprone (def) and N,N-donor ligands, 2,2ʹ-bipyridine (bpy) or 1,10-phenanthroline (phen), [VO2(def)(bpy)]⋅H2O (1) and [VO2(def)(phen)]⋅4H2O (2) were synthesized. The complexes were characterized by elemental analysis, spectral studies and single crystal X-ray diffraction analysis. The X-ray crystal structures of 1 and 2 reveal that both the complexes possess distorted octahedral coordination geometries with O4N2 coordination sphere around the vanadium center, and the deprotonated deferiprone occupying the equatorial plane. The complexes 1 and 2 efficiently catalyzed selective epoxidation of styrene with 30% H2O2 under ecologically sustainable organic solvent-free conditions, at ambient temperature. The catalysts afforded good styrene conversion and high TON value along with excellent epoxide selectivity (>99%). Recyclability of the catalysts at least up to three consecutive cycles without significant alteration in activity or selectivity, is an additional remarkable feature of the developed catalytic protocol.

Validated quantitative analysis method for routine residue monitoring of oxytetracycline and its 4-epimer in milk: Pipetting sample preparation and isocratic mobile phase HPLC-diode array under organic solvent-free conditions

The author introduces an organic solvent-free, small-scale, time shortening, economical procedure for quantitation of oxytetracycline (OTC) and its 4-epimer, 4-epi-oxytetracycline (4eOTC), in cow’s milk. Sample preparation was performed by homogenization using a handheld ultrasonic-homogenizer with water followed by Mono Tip® C18 pipette tip contains silica monolith bonded with octadecyl group with water eluent. The HPLC separation was achieved a C4 column with an isocratic aqueous mobile phase and a photodiode array detector (PDAD). The total time required for the analysis of one sample was less than 6 min. The method validation data were well within the international analytical method acceptance criteria. The limits of quantitation for OTC and 4eOTC were 0.035 and 0.048 μg/mL, respectively. The present technique may be proposed as an international standardized analytical method for routine residue monitoring for OTC and 4eOTC in milk.

Green Synthesis of Luminescent Gold-Zinc Oxide Nanocomposites: Cell Imaging and Visible Light-Induced Dye Degradation.

Green synthesis of gold-zinc oxide (Au-ZnO) nanocomposite was successfully attempted under organic solvent–free conditions at room temperature. Prolonged stirring of the reaction mixture introduced crystallinity in the ZnO phase of Au-ZnO nanocomposites. Luminescence properties were observed in these crystalline Au-ZnO nanocomposites due to in situ embedding of gold nanoparticles (AuNP) of 5–6 nm diameter on the surface. This efficient strategy involved the reduction of Au(III) by Zn(0) powder in aqueous medium, where sodium citrate (NaCt) was the stabilizing agent. Reaction time and variation of reagent concentrations were investigated to control the Au:Zn ratio within the nanocomposites. The reaction with the least amount of NaCt for a long duration resulted in Au-ZnO/Zn(OH)2 nanocomposite. X-ray photoelectron spectroscopy (XPS) confirmed the formation of Zn(OH)2 and ZnO in the same nanocomposite. These nanocomposites were reconnoitered as bioimaging materials in human cells and applied for visible light–induced photodegradation of rhodamine-B dye.

Deep eutectic solvent for the synthesis of (E)- Nitroalkene via microwave assisted Henry reaction

Deep eutectic solvents (DESs) are modified versions of ionic liquids and are formed by the fusion of polar components (liquids or solids) via hydrogen bonding interactions. In the present article, a new deep eutectic solvent (DES) was developed from ammonium acetate (as hydrogen bond acceptor- HBA) and ethylene glycol (as hydrogen bond donor- HBD) at 1:2 ratio. The physicochemical properties like density, viscosity, thermal stability and basicity of the mixture were studied. For the first time, DES was used as catalyst for the synthesis of nitroalkenes via microwave assisted Henry reaction under organic solvent free condition. The recyclability of the catalyst was achieved up to five runs without significant loss in the activity. The easy preparation, low-cost of starting materials, short reaction time etc. make the present catalyst more attractive.

Amino acid ionic liquids as efficient catalysts for CO2 capture and chemical conversion with epoxides under metal/halogen/cocatalyst/solvent-free conditions

Biocompatible amino acid ionic liquids (AAILs) were synthesized and efficiently applied in CO2 capture and catalysis for the coupling reaction of CO2 with epoxides under halogen-, cocatalyst- and organic solvent-free conditions.

Preparation of COOH-KCC-1/polyamide 6 composite by in situ ring-opening polymerization: synthesis, characterization, and Cd(II) adsorption study

A nanocomposite of carboxylic acid-functionalized fibrous silica KCC-1 and polyamide 6 (COOH-KCC-1/PA6 NC) was fabricated through an ultrasonic-assisted in situ ring-opening polymerization approach under an organic solvent-free condition. The presence of abundant functional groups like carboxylic, secondary amine, and ketone in the COOH-KCC-1/PA6 NC structure can make it a good candidate for the adsorption of heavy metals. Accordingly, COOH-KCC-1/PA6 NC was characterized and utilized as an adsorbent for Cd(II) uptake from aqueous media. Crucial adsorption factors, namely pH, adsorbent dosage, Cd(II) initial concentration, and contact time, affecting the removal of Cd(II) were monitored and the optimum adsorption conditions were determined. Isotherm and kinetic investigations were conducted and a non-linear fitting method of experimental data was used to obtain isotherm and kinetic parameters. The experimental maximum adsorption capacity of Cd(II) was found to be 109.2 mg g–1 (pH: 7.0, adsorbent dosage: 0.05 g, initial concentration: 80 mg L–1, time: 240 min, temperature: 25 ℃). The observed adsorption property is due to (1) the uniform distribution of COOH-KCC-1 filler within the PA6 matrix, (2) the presence of abundant adsorption sites like carboxylic acid (−COOH), ketone (–C=O), silanol (Si−OH), and secondary amine (–NH–) in the adsorbent structure, and (3) the structural stability of the adsorbent owing to strong interfacial interactions (physical and chemical bonding) between COOH-KCC-1 and PA6 polymer. Based on the results it can be suggested that the COOH-KCC-1/PA6 NC adsorbent can be handled for the adsorption of Cd(II) from aqueous media.

Alcohols selective oxidation with H2O2 catalyzed by robust heteropolyanions intercalated in ionic liquid-functionalized graphene oxide

A set of heteropolyacid-based ionic heterogeneous catalysts (PW@IL-GO(m)) have been synthesized by intercalated heteropolyanions in ionic liquid (IL)-functionalized graphene oxide (GO) via amino-protonation and/or anion-exchange reaction. This immobilization method offered improved dispersity, accessibility and stability of active sites. The amphipathic nature of IL-GO sheets and porosity of PW@IL-GO(m) are beneficial to reducing mass transfer limitation in a water/organic substrate two-phase system. Then, these obtained hybrids were employed as efficient and robust catalysts for the selective oxidation of alcohols into carbonyl compounds using hydrogen peroxide as an oxidant under organic solvent-free condition. As expected, PW@IL-GO(m) catalysts showed even much better activity than the corresponding homogeneous HPW (phosphotungstic acid) catalyst. Particularly, PW@IL-GO(1.5) gave a benzyl alcohol conversion of 94% and benzaldehyde chemoselectivity of 91%. Moreover, owing to the heterogeneous nature and strong cation–anion interactions between cationic supporter and PW anions, the as-prepared catalyst presented advantages of convenient recovery, simple preparation and steady reuse, further providing the industrial application potential in sustainable oxidation reactions.

Temperature-Controlled Chalcogenation and Chalcogenocyanation of Imidazopyridines in Water under Transition Metal-Free Conditions.

A sustainable and transition metal-free approach for C3 chalcogenation and chalcogenocyanation of imidazopyridines with KXCN (X = S or Se) has been developed under mild conditions. Importantly, this reaction was performed in the presence of catalytic iodine in aqueous medium, which afforded either chalcogenated or chalcogenocyanated imidazopyridines under temperature control. The current protocol featured a broad substrate scope, transition metal-free and organic solvent-free conditions, operational convenience, and gram-scale production.

Green Organic Solvent-Free Oxidation of Alkylarenes with tert-Butyl Hydroperoxide Catalyzed by Water-Soluble Copper Complex

AbstractDifferent benzylic compounds were efficiently oxidized to the corresponding ketones with aqueous 70% tert-butyl hydroperoxide (TBHP) and the catalytic system composed of CuCl2.2H2O and 2,2’-biquinoline-4,4’-dicarboxylic acid dipotassium salt (BQC). The catalytic system CuCl2/BQC/TBHP allows obtaining high yields at room temperature under organic solvent-free conditions. The interest of this system lies in its cost effectiveness and its benign nature towards the environment. Benzylic tertbutylperoxy ethers and benzylic alcohols were observed and suggested as the reaction intermediates. Analysis of organic products by atomic absorption did not show any contamination with copper metal. In terms of efficiency, CuCl2/BQC system is comparable or superior to the most of the catalytic systems described in the literature and which are based on toxic organic solvent.

Preparation and Application of Palladium Nanoparticle Impregnated Chloromethylated Polysulfone Matrix as an Efficient Catalytic Membrane for Oxidation of Alcohols

Abstract The use of palladium nanoparticles embedded in a chloromethylated Polysulfone (CMPSf) matrix was developed for highly efficient oxidation of primary and secondary alcohols to corresponding aldehyde and ketone in organic solvent free condition. Pd (Π)/bis (2, 4-dihydroxybenzaldehyde) chelate chemically incorporated onto CMPSf was used to prepare beneficial catalytic membranes. Chemical structure and thermal properties of resulting membranes were characterized via FTIR, 1HNMR, UV-vis, TGA and DSC techniques. Morphology and particle distribution throughout the catalytic membranes was elucidated using FE-SEM. An average particle size of Pd nanoparticles was estimated about 20 nm by XRD technique. ICP technique proved that no Pd particles were leached out of the membrane into the solutions; hence the as-prepared catalytic membranes could be used several times without significant loss in their activities. This is in good accordance with formation of chemical bond between Pd and polymer matrix.

Direct Hydroxylation of Phenol to Dihydroxybenzenes by H2O2 and Fe-based Metal-Organic Framework Catalyst at Room Temperature

A semi-crystalline iron-based metal-organic framework (MOF), in particular Fe-BTC, that contained 20 wt.% Fe, was sustainably synthesized at room temperature and extensively characterized. Fe-BTC nanopowders could be used as an efficient heterogeneous catalyst for the synthesis of dihydroxybenzenes (DHBZ), from phenol with hydrogen peroxide (H2O2), as oxidant under organic solvent-free conditions. The influence of the reaction temperature, H2O2 concentration and catalyst dose were studied in the hydroxylation performance of phenol and MOF stability. Fe-BTC was active and stable (with negligible Fe leaching) at room conditions. By using intermittent dosing of H2O2, the catalytic performance resulted in a high DHBZ selectivity (65%) and yield (35%), higher than those obtained for other Fe-based MOFs that typically require reaction temperatures above 70 °C. The long-term experiments in a fixed-bed flow reactor demonstrated good Fe-BTC durability at the above conditions.

An efficient synthesis of 2,3,5-trimethylbenzoquinone by metal-free oxidation of 1,2,4-trimethylbenzene

The oxidation of 1,2,4-trimethylbenzene with phthaloyl peroxide has been investigated under solvent-free and optimized conditions. 2,3,5-Trimethylbenzoquinone was obtained with great purity in 92% yield at 95% conversion of 1,2,4-trimethylbenzene at 120°C for 2.5 h under solvent-free conditions. The important factors such as the efficiency of the different cyclic acid anhydrides or carboxylic acid peroxides, the concentration of phthalic anhydride and 30% H2O2, the reaction time, the effect of solvent system, and the reaction temperature have been studied. An important advantage of this oxidizing system, aside from the organic solvent-free conditions, is that it is non-toxic, eco-friendly, and inexpensive. In addition, this methodology will be of great use in the preparation of commercially valuable benzoquinones from the corresponding aromatic compounds.

Silica gel-mediated self-aldol reactions of highly volatile aldehydes under organic solvent-free conditions without reflux condenser

Silica gel-mediated self-aldol reactions were catalyzed by piperidine to give the corresponding α,β-conjugated aldehydes in good yields. The aldol reactions of 4-nitro-, 4-trifluoromethyl-, and 4-chlorobenzaldehydes with acetone afforded the corresponding aldol products. Highly volatile aldehydes and acetone could be employed even without a reflux condenser for these reactions. Silica gel could be recycled five times without any significant decrease of the yields of the products.