Microwave-assisted Solvent-free Synthesis Research Articles

Selective and sensitive fluorescent and colorimetric chemosensor for detection of CO32- anions in aqueous solution and living cells

A new colorimetric and fluorescent chemosensor for visual determination of carbonate ions was developed by the microwave assisted solvent free synthesis of 7,8-dihydroxy-3-(4-methylphenyl) coumarin (DHMC). The structural characterization of DHMC was confirmed by microanalysis and spectroscopy methods (MALDI-TOF, FT-IR, 1H NMR, 13C NMR, and 2D HETCOR). The binding behaviors of DHMC were investigated towards various anions by UV–vis and fluorescence spectroscopy. DHMC showed a selective and sensitive fluorometric and colorimetric responses towards carbonate ion over other anions. The detection limit of CO32- was found to be 1.03 µM. Moreover, the fluorescence imaging in living cells suggests that DHMC has a great potential in the biological imaging application. It has been demonstrated that DHMC can be used as a rapid and reliable sensor for the determination of carbonate anion in a variety of practical applications.

Solvent-free microwave-assisted synthesis of aripiprazole

Solvent-free microwave-assisted synthesis of aripiprazole

Coumarin Derivatives Solvent-Free Synthesis under Microwave Irradiation over Heterogeneous Solid Catalysts.

A suitable methodology of synthesis of coumarin derivatives by Pechmann reaction over heterogeneous solid acid catalysts in a free solvent media under microwave irradiation is described. Resorcinol, phenol and ethyl acetoacetate were selected as model reactants in the Pechmann condensation. The catalytic activity of several materials—Amberlyst-15, zeolite β and sulfonic acid functionalized hybrid silica—in solvent-free microwave-assisted synthesis of the corresponding coumarin derivatives has been investigated in detail. 7-Hydroxy-4-methylcoumarin and 4-methylcoumarin were obtained in 97% and 43% yields, respectively, over Amberlyst-15. This was the most active catalyst in the Pechmann reaction under studied conditions.

Green synthesis and crystal structure of 3-(benzo-thia-zol-2-yl)thio-phene.

The title compound, C11H7NS2, was prepared in high yield (87%) using a solvent-free microwave-assisted synthesis. The structure shows whole-mol-ecule disorder with occupancies for two orientations (A and B) of 0.4884 (10) and 0.5116 (10), respectively. The thio-phene and benzo-thia-zole rings are almost planar and make dihedral angles of 10.02 (18) and 12.54 (19)° for orientations A and B, respectively. Slipped π-π stacking between the aromatic rings, together with C-H⋯π, C-H⋯S and C-H⋯N inter-actions, result in a herringbone motif in the crystal packing.

Solvent-free microwave-assisted synthesis of solketal from glycerol using transition metal ions promoted mordenite solid acid catalysts

The present study demonstrates a clean and green approach for the production of bio-fuel additives from renewable glycerol acetalization using microwave irradiation as heating method. Various transition metal ion (M=Fe-, Co-, Ni-, Cu- & Zn-) promoted mordenite solid acid catalysts were prepared by wet impregnation method and examined for the acetalization of glycerol with acetone. Investigation of the structural and chemical properties of the catalysts was achieved using XRD, FT-IR, TGA-TPD, SEM/EDX and XPS techniques. Comparative studies using conventional heating were performed in order to study the efficiency of microwave-assisted acetalization reactions. The effect of various operating parameters on the catalytic activity studies was examined. Amongst the metal-promoted mordenite catalysts tested, Cu-Mor had the best performance due to the presence of a large amount of acidic sites and the synergetic effects of metal particles interacting with mordenite. Microwave-assisted acetalization of glycerol into Solketal was found to be an energy efficient route for glycerol valorization achieving 98% selectivity to solketal at 95% glycerol conversion during a reaction time of 15min over Cu-Mor catalyst and acetone/glycerol at a molar ratio of 3:1. Reuse of spent catalyst showed good repeatability for up to four reaction cycles with a marginal decrease in conversion.

Nitrones and nucleobase-containing spiro-isoxazolidines derived from isatin and indanone: solvent-free microwave-assisted stereoselective synthesis and theoretical calculations

Here, we present a highly efficient approach to nucleobase-containing spiro-isoxazolidines with potential biological activity starting from isatinyl/indanyl nitrones.

Microwave-assisted solvent-free catalyzed synthesis and luminescence properties of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent

A solvent-free microwave-assisted four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent was studied by condensation of p-phenylenediamine, aryl diketone, benzaldehyde derivatives and ammonium acetate in the presence of solid support silica gel and catalyst Keggin-H3[PW12O40]. The effects of four components molar ratio along with catalyst loading, irradiation time on the yields were investigated. Also, the structures of synthesized compounds were characterized by FT-IR, HRMS, 1H NMR and 13C NMR spectroscopy. Furthermore, their ultraviolet–visible maximum absorption, liquid fluorescence emission maximum and quantum yields were, respectively, measured in 0.05 M H2SO4 aqueous solution and in dichloromethane. Simultaneously, solid fluorescence spectra were determined in the powder state. The relationships between the optical behavior and the polarity of the solvents for some compounds were assessed. The results showed that the fluorescence quantum efficiency was increased by introducing amino phenyl in comparison with benzyl on 1-position of trisubstitued imidazoles. The compounds synthesized were sensitive to the polarity of the solvents.

Efficient Microwave-Assisted Solvent-Free Synthesis and Molecular Docking Studies of 2-pyridone derivatives as Anticancer Agents and Evaluation of Cytotoxic Effects

Introduction: A green protocol will be used to synthesize a novel series of 3-cyano-5- arylazo-pyridones (9a-c) and (10d-i). Methodology: Structures of the new products will be confirmed on the basis of spectroscopic data (FT-IR, 1D, NMR) as well as alternative synthetic routes, anticancer cell-line will be investigated and also molecular docking studies will be applied. Results: The activity against different cancer cell-line will be studied. Compounds with electron withdrawal group showed the highest activities.

Solvent-free microwave-assisted synthesis and biological evaluation of 2,2-dimethylchroman-4-one based benzofurans

Abstract A series of novel chroman-4-one fused benzofurans were synthesized by cyclization of the corresponding chalcones under microwave irradiation. All new compounds were characterized by IR, 1H NMR, 13C NMR and mass spectral data and were evaluated for their in vitro antimicrobial and antioxidant activities.

Solvent-free microwave-assisted synthesis and biological evaluation of aurones and flavanones based on 2,2-dimethylchroman-4-one

A series of novel 8-aryl-2,2-dimethyl-2,3,7,8-tetrahydropyrano[3,2-g]chromene-4,6-dione and 2-arylidene-7,7-dimethyl-6,7-dihydro-2H-furo[3,2-g]chromene-3,5-dione derivatives have been synthesized by oxidation of the corresponding chalcones under microwave irradiation. All newly synthesized compounds were characterized by IR, 1H, 13C NMR, and mass spectra and valuated for their in vitro antibacterial and antifungal activities.

A rapid and efficient solvent-free microwave-assisted synthesis of pyrazolone derivatives containing substituted isoxazole ring

An efficient synthesis of 4-substituted pyrazolone derivatives was developed. 4-Substituted pyrazolone derivatives were synthesized in 78–97% yields starting from various 3-substituted isoxazole-5-carbaldehydes, ethyl acetoacetate and hydrazine under microwave irradiation and solvent-free conditions, and were characterized by HRMS, FTIR, 1H NMR and 13C NMR spectroscopy. SiO2 was found to possess favorable catalytic activity and dispersancy for the condensation reaction. The merits of this method include the environmentally friendly reaction conditions, simple operation, broad substrate, satisfied yields and the reuse of the silica. Moreover, the crystal structure of the compound 2-(4-chlorophenyl)-4-((1-(4-chlorophenyl)-5-hydroxy-3-methyl-1H-pyrazol-4-yl)(3-phenylisoxazol-5-yl)methyl)-5-methyl-1H-pyrazol-3(2H)-one (5a) in the monoclinic space group C2/c was presented.

Microwave-assisted solvent-free synthesis of new polyimine

AbstractMicrowave irradiation method indicated points of interest for the produced polymer that contrasted with that prepared by a routine strategy, where it can offer a polymer in brief time, high yield, higher molecular weight because of the prevention action of the chain exchange, more pure compounds, and all the more thermally stable polymers, instead of the conventional technique. Benzil and p-phenylenediamine were built into the main chain to prepare a new polymer named polyimine, utilizing microwave route as a part of 95% yield, and characterized it by Fourier transform infrared (FT-IR), UV–visible, and nuclear magnetic resonance (NMR) techniques. The thermal properties of the new polymer were evaluated by thermal gravity analysis (TGA).

Microwave-assisted solvent-free synthesis of imidazo[1,2-a]pyridines via a three-component reaction

A facile microwave-assisted three-component reaction of pyridin-2-amine, 3-phenylpropiolaldehyde and alcohol is catalyzed by TsOH under solvent-free conditions to give corresponding imidazo[1,2-a]pyridines in good yields. Reactions proceed with high efficiency and good functional group tolerance. This approach provides a useful protocol for the preparation of functionalized imidazo[1,2-a]pyridine derivatives.

Solvent-free microwave-assisted synthesis of novel pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidines with potential antifungal activity

Novel fused pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidines 5 were prepared by a solvent-free microwave assisted reaction of heterocyclic o-aminonitriles 3 and cyanopyridines 4 in the presence of tBuOK as catalyst. This protocol provides a versatile procedure for the synthesis of the title compounds with the advantages of easy work-up, mild reaction conditions and good yields. All compounds were also tested for antifungal properties against two clinically important fungi; Candida albicans and Cryptococcus neoformans. Several compounds showed moderate activity against both fungi, being 5a the most active compound. Analysis of the antifungal behavior of properly grouped compounds allowed to determine that the position of the N in the pyrimidyl moiety per se does not play a role in the activity. In turn, the type of 4-R substituent appears to influence the activity. In addition to the above considerations, the lipophilicity of compounds measured as logP showed to be not related to the activity and regarding the dipole moment (D), no net correlation was observed, although it is the most active compounds (% inhibition >50%) that have a D⩾7.5, mainly against C. albicans.

Crystal structure of the di-Mannich base 4,4'-di-chloro-3,3',5,5'-tetra-methyl-2,2'-[imidazolidine-1,3-diylbis(methyl-ene)]diphenol.

The title compound, C21H26Cl2N2O2, was prepared in a solvent-free microwave-assisted synthesis, and crystallizes in the ortho-rhom-bic space group Pna21. The imidazolidine ring adopts an envelope conformation and its mean plane is almost perpendicular to the two pendant aromatic rings [dihedral angles = 84.61 (9) and 86.54 (9)°]. The mol-ecular structure shows the presence of two intra-molecular O-H⋯N hydrogen bonds between the phenolic hy-droxy groups and imidazolidine N atoms. The two 3-chloro-6-hy-droxy-2,4-di-methyl-benzyl groups are located in a cis orientation with respect to the imidazolidine fragment. As a result, the lone pairs of electrons on the N atoms are presumed to be disposed in a syn conformation. This is therefore the first example of an exception to the 'rabbit-ears' effect in such 2,2'-[imidazolidine-1,3-diylbis(methyl-ene)]diphenol derivatives.

Microwave assisted synthesis and biomedical potency of salicyloyloxy and 2-methoxybenzoyloxy androstane and stigmastane derivatives

A convenient microwave assisted solvent free synthesis as well as conventional synthesis of salicyloyloxy and 2-methoxybenzoyloxy androstane and stigmastane derivatives 7–19 from appropriate steroidal precursors 1–6 and methyl salicylate is reported. The microwave assisted synthesis in most cases was more successful regarding reaction time and product yields. It was more environmentally friendly too, compared to the conventional method. The antioxidant activity and cytotoxicity of the synthesized derivatives were evaluated in a series of in vitro tests, as well as their inhibition potency exerted on hydroxysteroid dehydrogenase enzymes (Δ5-3βHSD, 17βHSD2 and 17βHSD3). All of the tested compounds were effective in OH radical neutralization, particularly compounds 9, 11 and 14, which exhibited about 100-fold stronger activity than commercial antioxidants BHT and BHA. In DPPH radical scavenging new compounds were effective, but less than reference compounds.2-Methoxybenzoyl ester 10 exhibited strong cytotoxicity against MDA-MB-231 cells. Most compounds inhibited growth of PC-3 cells, where salicyloyloxy stigmastane derivative 15 showed the best inhibition potency. Compounds 9, 10 and 11 were the best inhibitors of 17βHSD2 enzyme. X-ray structure analysis and molecular mechanics calculations (MMC) were performed for the best cytotoxic agents, compounds 10 and 15. A comparison of crystal and MMC structures of compounds 10 and 15 revealed that their molecules conformations are stable even after releasing of the influence of crystalline field and that the influence of crystal packing on molecular conformation is not predominant.

One-pot microwave-assisted solvent-free synthesis, theoretical and experimental studies on barrier rotation of C–N bond of N-alkenyl-1,2,3-triazoles

The reactions on benzotriazoles continue to happen to reach interesting varieties of their derivatives. This study reports a fast one-pot microwave-assisted solvent-free synthesis of N-alkenyl-1,2,3-benzotriazole (3, 5, and 7) and 1-(2-Alkyloxycarbonyl-vinyl)-1H-[1–3] triazole-4-carboxylic acid methyl ester (8 and 9) derivatives by nucleophilic addition reactions of 1,2,3-benzotriazole (C6H5N3) (1) and 1H-[1–3] triazole-4-carboxylic acid methyl ester (C4H4N3O2) (1′) with R-propiolates (R = Me, Et; 2 & 4) and phenylacetylene 6 in good yields. The values of activation energy for rotation around C–N bond in the synthesized N-alkenyl-1,2,3-triazole compounds were studied by DFT-B3LYP/6-31G* method.

Novel route for silylation of silica gel and aliphatic amines immobilization based on microwave-assisted solvent free synthesis and their applications for Cu(II) and Fe(III) removal from natural water samples

This article describes a new route for silica gel silylation and immobilization of aliphatic amines based on microwave-assisted solvent free synthesis to produce new solid phase extractors. The mode of synthesis was optimized under microwave conditions and achieved in a short time without using solvents. The produced phases named: silica gel- monoamine (SG-MA), silica gel- ethylenediamine (SG-EDA) and silica gel- diethylenetriamine (SG-DETA). The selectivity of these phases towards the uptake of Cu(II) and Fe(III) was checked using batch equilibration technique. Microwave radiation power and time of radiation were optimized to obtain the highest metal uptake values. The novel synthesized silica amine phases were characterized using Fourier transform infrared spectra and scanning electron microscope. The effects of different parameters including, hydrogen ion concentration, initial metal ion concentration, mass of the phase and shaking time on binding capacities of both Cu(II) and Fe(III) were explored. Results of sorption isotherms of the phases were better fitted with the Langmuir model (r2 ≥ 0.950). In addition, the kinetics data were best fitted with the pseudo–second-order type (r2 = 0.999). Application of SG-MA for removal of Cu(II)- and Fe(III)-spiked natural water samples was achieved satisfactorily using batch experiments. The results were found to refer to superior recovery percentages (90.0–97.01 ± 0.010–0.521%) with no significant matrix interferences.

Microwave-assisted solvent-free synthesis of fluorescent naphthalimide dyes

A series of fluorescent naphthalimide dyes were synthesized via aromatic nucleophilic substitution reaction of 4-bromo-N-alkylnaphthalimides with amines, alkoxides and thiols under microwave irradiation. In this procedure an efficient method for C–N, C–O and C–S bond formation via applying appropriate nucleophiles in the presence of KF/Al2O3 under solvent-free conditions is described. Adducts are produced in good to excellent yields and relatively in short times. The optical properties of three dyes as representative derivatives were examined by UV absorption and steady state fluorescence spectroscopy in solvents with different polarity.

Microwave-assisted solvent-free synthesis of 14-aryl/alkyl-14H-dibenzo[a,j]xanthenes and tetrahydrobenzo[a]xanthen-11-ones catalyzed by nano silica phosphoric acid

Article history: Received June 29, 2012 Received in Revised form November 6, 2012 Accepted 16 December 2012 Available online 16 December 2012 Nano silica phosphoric acid (nano SPA) was applied as a catalyst for synthesis of 14-aryl/alkyl-14H-dibenzo[a,j]xanthenes and tetrahydrobenzo[a]xanthen-11-ones in microwave oven under solvent free conditions. High efficiency, easy availability and reusability are some advantages of this catalyst. © 2013 Growing Science Ltd. All rights reserved.