Solvent-free Microwave Irradiation Research Articles

Microwave and Ultrasound-assisted Facile Synthesis of 2’-Hydroxychalcones

In this work, solvent-free microwave irradiation and ultrasonication in an ethanol-water solvent system were presented as viable methods for the synthesis of 2’-hydroxychalcones in a sustainable and facile way via base-catalyzed Claisen-Schmidt condensation from readily available 2’-hydroxyacetophenones and benzaldehydes. Additionally, the synthesis of 3-hydroxyflavone through in-situ oxidative cyclization of a 2’-hydroxychalcone intermediate in a one-pot, two-step approach under ultrasonication is also performed.

Utilization and evaluation of catalytic activity of hydroxyapatite on the synthesis of some corosolic acid amide

Hydroxyapatite was employed as a catalyst for the synthesis of 17C-corosolic amide by the condensation of 17C-corosolic acid chloride and phenyl hydrazide under solvent-free microwave irradiation technique. In this condensation the obtained yield is more than 87%. Within this condensation the catalytic activity and reusability of this hydroxy apatite was investigated on the basis of percentage of yield. The prepared amide was characterized by their analytical and spectroscopic data.

Copper(II)/polyimide linked covalent organic framework as a powerful catalyst for the solvent-free microwave irradiation-based synthesis of 2,4,5-trisubstituted imidazoles.

Copper(II)/polyimide-linked covalent organic frameworks under solvent-free and microwave-assisted conditions have been used in an efficient one-pot protocol for the preparation of 2,4,5-trisubstituted imidazoles via benzil, aromatic aldehydes and ammonium acetate. By applying solvent-free conditions and microwave irradiation, three-component condensation provides safe operations, low pollution, quick access to products, and an easy set-up. As a result of its reusability, the catalyst can also be reutilized for many runs without missing any activity.

Cu(II)/polyimide linked COF: An effective mesoporous catalyst for solvent-free 1,5-benzodiazepine synthesis

Copper(II)@polyimide linked covalent organic frameworks (Cu@PI-COF) under solvent-free and microwave assisted conditions have been used in an efficient one-pot protocol for the preparation of 1,5-benzodiazepines via 1,2-diaminobenzene, aromatic aldehydes and dimedone. By applying solvent-free conditions and microwave irradiation, three-component condensation provides safe operations, low pollution, quick access to products, and an easy set-up. As a result of its reusability, the catalyst can also be reutilized many runs without missing any activity.

Understanding the Raman enhancement of carbon nanohorns labelled with organic dyes.

Carbon nanohorns have been non-covalently functionalized with two different benzothiadiazoloquinoxalines prepared via Stille cross-coupling reactions under solvent-free conditions and microwave irradiation. The close interactions between these organic molecules and the nanostructures resulted in a prominent Raman enhancement, which makes them attractive candidates for multiple applications. A complete experimental physico-chemical characterization has been combined with in silico studies to understand these phenomena. The processability of the hybrids was exploited to prepare homogeneous films on substrates with different natures.

Solvent free, microwave-assisted synthesis and cytotoxicity evaluation of benzoxazole derivatives

Introduction: This work aims to develop an efficient green synthetic procedure and cytotoxicity evaluation of benzoxazole derivatives, an essential building block in medicinal chemistry research owing to its broad range of pharmacological properties, especially anticancer activity. Methods: The microwave-assisted condensation reaction between 2-amino-4-methylphenol and aromatic aldehydes using iodine as the oxidant under solvent-free conditions was explored. The cytotoxicity of the prepared benzoxazoles against the three human cancer cell lines including Lu-1, Hep-G2 and MCF-7 were examined using a MTT assay. Results: Five 2,5-disubstituted benzoxazole derivatives have been successfully synthesized in good yields (67-90%) using iodine as the oxidant under solvent-free microwave irradiation conditions. The initial cytotoxicity evaluation of the four synthesized compounds revealed that compounds 3b and 3e exhibited good activity against MCF-7 (IC50 = 12 μg/mL) and Hep-G2 (IC50 = 17.9 μg/mL), respectively. Remarkably, compound 3c showed the best cytotoxicity against MCF-7 at IC50 = 4 μg/mL. Conclusion: Microwave irradiation effectively assisted the condensation reaction between 2-amino-4-methylphenol and aromatic aldehydes in the presence of iodine under solvent-free conditions to facilitate the desired benzoxazoles in good total yields. The prepared benzoxazoles proved to be potent candidates for further study in the development of anticancer agents.

Bis(phenyl-β-diketonato)titanium(IV) ethoxide complexes: Ring-opening polymerization of l-lactide by solvent-free microwave irradiation

A range of functionalized bis(phenyl-β-diketonato)titanium(IV) ethoxide complexes of the type [Ti(L)2(OEt)2], containing two asymmetric or symmetric phenyl-β-diketonate ligands (L), have been synthesized and fully characterized. Single crystal X-ray diffraction has been used to confirm that all structures crystallize with the ethoxide ancillary ligands in a cis arrangement and NMR spectra show characteristic ligand rearrangement in solution. The complexes have been screened as catalysts in the ring-opening polymerization (ROP) of l-lactide (L-LA) to yield polylactide (PLA), by using microwave (MW) and conventional heating. The resulting polymers have high molecular weights but a high polydispersity index (PDI) which is suggestive of transesterification. However, unlike conventional heating methods, the polymerization by MW reaction leads to a retention in stereochemistry of the resulting polymer in significantly shorter time periods.

Oxidation of Cyclohexanol and Cyclohexanone by Monochromate Ions in Organic Solvents and on Solvent Free Microwave Irradiation under Phase Transfer Catalysis - A Comparative Study

Oxidation of cyclohexanol and cyclohexanone were carried out by acidified monochromate ions in ethyl acetate and toluene under phase transfer catalysis and also in solvent free condition under microwave irradiation. The extraction of monochromate ions from aqueous medium to organic phase was carried by employing various phase transfer catalysts in the presence of mineral acids. The effect of [catalyst] and [mineral acid] on extraction of monochromate from aqueous phase to organic phase was also studied. The product obtained, namely adipic acid obtained with both reactants was characterized by its melting point and infrared spectral technique. The reaction was over within 15 min with more than 85% yield at a temperature of 323 K under microwave irradiation where as it gave around 70% yield at 353 K within 150 min under phase transfer catalysis condition. The enhanced reaction rate and high yield of product substantiate the application of phase transfer catalytic technique under microwave irradiation for organic synthesis. A suitable mechanism for the oxidation of substrates by monochromate under phase transfer catalysis is also suggested.

A One-pot Synthesis of Novel Derivatives of Oxadiazine-4-thione, and its Antibacterial Activity, and Molecular Modeling Studies.

The synthesis of a novel series of oxadiazine-4-thione biological molecules was executed through the incorporation of the ortho-, meta-, and para-benzoyl isocyanates to the tetrabromophthalimide nucleus. A one-pot multicomponent methodology in a solvent-free microwave irradiation environment was employed to afford this series of oxadiazine-4-thione, deriving a comparison with the conventional method. Subsequently, the yielded derivatives were subjected to further biological assessment. The acquired results denoted that the one-pot procedure, which delivered products in a 2-4 min. interval, was more efficient in evaluation against the classical method, which consumed a 1-2:30 hr. interval. The application of the antibacterial analyses was subjected to all the compounds, resulting in molecules 6a and 6c demonstrating the highest activity regarding Aspergillus Favus; molecules 5b and 5c exhibiting an equivalent level of activity towards E-coli and Fusarium Moniliform; and molecules 4b, 4c, 5b, and 5c presenting an identical level of activity to the aforementioned derivatives involving Staphylococcus. Concluison: Molecular modeling studies by the MOE, the preceding antibacterial behavior was conducted to advocate the newly prepared compounds. Moreover, the spectroscopic approaches were exploited to verify and establish the structures and mechanisms of the synthesized derivatives' reactions.

Improving the electrochemical performance of a natural molybdenite/N-doped graphene composite anode for lithium-ion batteries via short-time microwave irradiation.

In the present work, low-cost natural molybdenite was used to make a MoS2/N-doped graphene composite through coulombic attraction with the aid of (3-aminopropyl)-triethoxysilane and the electrochemical performance was greatly improved by solvent-free microwave irradiation for tens of seconds. The characterization results indicated that most (3-aminopropyl)-triethoxysilane can decompose and release N atoms to further improve the N-doping degree in NG during the microwave irradiation. In addition, the surface groups of N-doped graphene were removed and the particle size of MoS2 was greatly decreased after the microwave irradiation. As a result, the composite electrode prepared with microwave irradiation exhibited a better rate performance (1077.3 mA h g−1 at 0.1C and 638 mA h g−1 at 2C) than the sample prepared without microwave irradiation (1013.6 mA h g−1 at 0.1C and 459.1 mA h g−1 at 2C). Therefore, the present results suggest that solvent-free microwave irradiation is an effective way to improve the electrochemical properties of MoS2/N-doped graphene composite electrodes. This work also demonstrates that natural molybdenite is a promising low-cost anode material for lithium-ion batteries.

Efficient Solvent-Free Microwave Irradiation Synthesis of Highly Conductive Polypropylene Nanocomposites with Lowly Loaded Carbon Nanotubes

Efficient Solvent-Free Microwave Irradiation Synthesis of Highly Conductive Polypropylene Nanocomposites with Lowly Loaded Carbon Nanotubes

The crystal structure and DFT studies on (E)-1-benzyl-N-(4-chlorobenzylidene)piperidin-4-amine

(E)-1-Benzyl-N-(4-chlorobenzylidene)piperidin-4-amine was prepared by greener, solvent-free microwave irradiation of 4-amino-N-benzyl piperidine with 4-chloro benzaldehyde utilizing a successful ZnFe2O4 catalyst. The greener technique offered better yield. The crystal (E)-1-benzyl-N-(4-chlorobenzylidene)piperidin-4-amine [C19H21N2Cl] has been developed by slow solvent evaporation method at room temperature. The unit cell measurements are recorded by single crystal X-ray diffraction. The XRD study demonstrated the crystallinity of the sample. Single crystal XRD predict the structure of title compound and it’s has a place with the orthorhombic system with P21 space group. Theoretical calculations were performed utilizing density functional theory (DFT) method.

Cu(II) and Fe(III) Complexes Derived from N-Acetylpyrazine-2-Carbohydrazide as Efficient Catalysts Towards Neat Microwave Assisted Oxidation of Alcohols

The mononuclear Cu(II) complex [Cu((kNN′O-HL)(H2O)2] (1) was synthesized using N-acetylpyrazine-2-carbohydrazide (H2L) and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray crystallography. Two Fe(III) complexes derived from the same ligand viz, mononuclear [Fe((kNN′O-HL)Cl2] (2) and the binuclear [Fe(kNN′O-HL)Cl(μ-OMe)]2 (3) (synthesized as reported earlier), were also used in this study. The catalytic activity of these three complexes (1–3) was examined towards the oxidation of alcohols using tert-butyl hydroperoxide (TBHP) as oxidising agent under solvent-free microwave irradiation conditions. Primary and secondary benzyl alcohols (benzyl alcohol and 1-phenylethanol), and secondary aliphatic alcohols (cyclohexanol) were used as model substrates for this study. A comparison of their catalytic efficiency was performed. Complex 1 exhibited the highest activity in the presence of TEMPO as promoter for the oxidation of 1-phenylethanol with a maximum yield of 91.3% of acetophenone.

Microwave assisted synthesis and photophysical properties of blue emissive 2-amino-3-carboxamide-1,1′-biaryls and 4-(arylamino)-[1,1′-biphenyl]-3-carboxamides via Suzuki and Chan-Evans-Lam coupling

An efficient microwave assisted synthesis of 2-amino-3-carboxamide-1,1′-biaryls derivatives 4a-p and terphenyl derivative 5a from 2-amino-5-iodobenzamide 2a, 2-amino-3,5-diiodobenzamide 2b and (het)aryl boronic acids via Suzuki coupling has been achieved. Synthetic utility of the product 4-amino-4′-cyano-[1,1′-biphenyl]-3-carboxamide 4j has been demonstrated for the synthesis of 4-(aryl amino)-[1,1′-biphenyl]-3-carboxamide derivatives 10a-c via Chan-Evans-Lam coupling reaction. Furthermore, 4-(4′-oxo-3′, 4′-dihydro-1′H-spiro[fluorene-9,2′-quinazolin]-6′-yl)benzonitrile 12a was obtained from biaryl derivative 4j and fluorenone 11a and 6(4- methoxyphenyl)2-(ferrocenyl) quinazolin-4(3H)-one 12b from biaryl derivative 4k and ferrocenealdehyde 11b using phosphotungstic acid as green catalyst and solvent free microwave irradiation condition. Remarkably, all the synthesized 2-amino-3-carboxamide-1,1′-biaryls and 4-(aryl amino)-[1,1′-biphenyl]-3-carboxamide derivatives 4a-p showed luminescence in the blue region with large Stokes shift. Significantly, 2-amino-3-carboxamide-1,1′-biaryls 4d and 4j showed high fluorescence quantum yields (Φf) 0.54 and 0.84, respectively.

Crystal Structure, Hirshfeld Analysis and DFT Study of 6,7-Dimethoxy-3-[(5-Chloro-1,3,3-Trimethylindolin-2-Ylidene)Methyl]Isobenzofuran-1(3h)-One

The coupling reaction of 5-chloro-1,3,3-methylenindoline with 6-formyl-2,3-dimethoxy benzoic acid under solvent-free microwave irradiation gave of 6,7-dimethoxy-3-[(5-chloro-1,3,3-trimethylindolin-2-ylidene)methyl]isobenzofuran- 1(3H)-one, C22H22ClNO4 in high yield. The molecular structure consists of indoline system (C1-C8/N1) and isobenzofuran system (C10-C17/O1) connected by the enamine carbon. The title compound is crystallised in P21/n space group, Z’=4 with two independent molecules in centrosymmetric dimer. By using Hirshfeld surface and two-dimensional fingerprint plots, the presence of short intermolecular interactions and π-π stacking in the crystal structure were analysed. The DFT study is performed by comparing the calculation data with the X-ray data and analysing the HOMO and LUMO value, which gave -0.26952 a.u. and -0.17760 a.u., respectively.

Sodium acetate/MWI: a green protocol for the synthesis of tetrahydrobenzo[α]xanthen-11-ones with biological screening

An efficient, straightforward and rapid method has been developed for the synthesis of tetrahydrobenzo[α] xanthen-11-one using sodium acetate. The reaction was performed via three components: β-naphthol, dimedone with various aromatic aldehydes under solvent-free microwave irradiation and conventional heating condition. We observed an efficient result for microwave synthesis than conventional heating. The synthesized tetrahydrobenzo[α]xanthen-11-one (4a–l) was screened for their antimicrobial activity against two bacteria (Escherichia coli and Bacillus subtilis) and two fungal strains (Aspergillus niger and Saccharomyces cerevisiae). The synthesized products: 9, 10-dihydro-9, 9-dimethyl-12-(4-nitrophenyl)-8H-benzo[a]xanthen-11(12H)-one, 9, 10-dihydro-9, 9-dimethyl-12-(2, 4-dichlorophenyl)-8H-benzo[a]xanthen-11(12H)-one, 9, 10-dihydro-9, 9-dimethyl-12-(6-methyl-4-oxo-4H-chromen-3-yl)-8H-benzo[a]xanthen-11(12H)-one exhibit good antimicrobial activity. The developed protocol is graced with appealing advantages such as high purity, simple operation, excellent yields, inexpensive and easy availability of catalyst.

Microwave Irradiation Syntheses and Crystal Structures of Two Series of Novel Fivemembered Heterocyclic Mono-Imine Compounds.

The late transition metal complexes with five-membered heterocyclic mono-imine ligands have attracted much attention because of their potential application in olefin polymerization catalysis. In order to increase the coordination ability of heteroatom N and S to center metals, CH3 group was introduced into the side arm of pyrrole imine and thiophene imine respectively, to get two series of novel five-membered heterocyclic imine compounds, mono(imino)pyrroles and mono(imino)thiophenes. Two series of novel five-membered heterocyclic compounds with the mono-imine group were synthesized from the p-toluene sulfonic acid catalyzed Schiff base condensation of aromatic amines and 2-acetylpyrrole/ 2-acetylthiophene respectively, using CH3 group to substitute the common H atom on the side arm of pyrrole imine/ thiophene imine. All the heterocyclic mono-imine compounds were characterized adequately by means of 1H NMR, 13C NMR, FT-IR, elementary analysis, as well as X-ray crystallographic diffraction. The reactivity differences between two precursor 2-acetylpyrrole and 2-acetylthiophene with aromatic amines were compared and discussed in detail. Compared to traditional heating methods, the solvent-free microwave irradiation seemed more efficient to prepare these series of five-membered heterocyclic mono-imine compounds, which resulted in a higher yield and cleaner product.

Friedel-Crafts alkylation of aromatic derivatives using deep eutectic solvent ZnCl2/ethylene glycol

Deep eutectic solvent ZnCl2/ethylene glycol synthesized from ethylene glycol and zinc chloride was investigated for the Friedel-Crafts alkylation of benzene derivatives with benzyl bromide at 120oC under solvent-free microwave irradiation. The reaction was carried out under mild condition with high conversion, high regioselectivity, and short reaction time. Moreover, the catalyst can be recovered and reused without significant loss of the catalytic activity. This method can be applied on industrial processes in the future.

Porous metal oxides derived from Cu–Al layered double hydroxide as an efficient heterogeneous catalyst for the Friedel–Crafts alkylation of indoles with benzaldehydes under microwave irradiation

Four Cu-Mg-Al mixed metal oxides (MMO) were synthesized through the calcination of layered double hydroxides (LDHs). These catalysts were fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller surface area (BET), and inductively coupled plasma optical emission spectrometer (ICP-OES). The catalytic efficiency of porous metal oxides derived from LDHs has been tested successfully for the synthesis of bis(indolyl)methanes via the Friedel–Crafts alkylation of indoles with aromatic aldehydes under solvent-free microwave irradiation. The Cu-Al MMO showed the best catalytic activity to produce the expected products up to 98% yield and 100% selectivity for only 20 min under solvent-free microwave irradiation. Moreover, the catalyst can be recovered quickly from the reaction mixture by filtration and reused several times without significant loss of the reactivity.

Synthesis of Highly Sensitive Fluorescent Probe Based on Tetrasubstituted Imidazole and Its Application for Selective Detection of Ag+ Ion in Aqueous Media

A small molecule fluorescent probe, 4-[2-(4-chlorophenyl)-4,5-diphenyl-1H-imidazol-1-yl]aniline(L) for detecting Ag+ ion was gently synthesized via one-pot multi-component reaction catalyzed by H3[PW12O40] under solvent-free microwave irradiation. When the concentration of Ag+ ion changed from 0 to 8.0×10−6 mol/L in the solution of H2O/CH3OH(19:1, volume ratio), the fluorescence emission spectrum was blue-shifted and accompanied by a gradual increase in fluorescence intensity with a low detection limit of 3.0×10−11 mol/L. Moreover, UV-Vis absorption titration experiment demonstrated a 1:1 stoichiometric ratio and an association constant of (9.95±0.44)×105 L/mol between probe L and Ag+ ion, and thus their complexation mechanism was also proposed and verified. More importantly, this fluorescent probe was remarkably specific for Ag+ ion under the interference of other metal ions and exhibited a wide pH application range of 4.0―8.0. Additionally, preliminary application of this probe was also carried out and satisfactory results were shown.