Microwave-assisted Condensation Research Articles

Microwave-assisted synthesis of thiazolothiazole-containing conjugated polymers as promising charge-transport materials for perovskite solar cells

The synthesis of novel thiazolo[5,4-d]thiazole-containing conjugated polymer was performed by three alternative methods, namely, by the Stille or Suzuki cross-coupling as well as microwave-assisted condensation reaction with carbonyl precursor and dithioxamide. The latter way is straightforward and efficient for the design of novel materials with desirable optoelectronic and physicochemical characteristics providing an encouraging hole-transport properties and comparable performance of perovskite solar cells.

Dye-sensitized solar cells on TiO2 photoelectrodes sensitized with rhodamine

Rhodamine-6G derivative Rhd, synthesized by microwave-assisted condensation of rhodamine hydrazide and 2-Amino-3-formylchromone, and its metal complexes were investigated using ultraviolet–visible (UV–vis) and fluorescence spectroscopy. Dye-sensitized solar cells (DSSCs) were fabricated using Rhd and its metal complexes with aluminum (Al3+) and chromium ions (Cr3+). Current-density (I-V) characteristics and Electrochemical Impedance Spectroscopy (EIS) measurements of the rhodamine dyes were conducted to determine their solar-to-electric power efficiencies and electron lifetimes. The solar cell sensitized with Rhd and Cr3+ had the highest solar to electric power efficiency at 0.16 %.

Performance of Rhodamine-Sensitized Solar Cells Fabricated with Silver Nanoparticles

A plasmonic effect of silver nanoparticles (AgNPs) in dye-sensitized solar cells (DSSCs) is studied. In this investigation, the efficiency of dye-sensitized solar cells has been remarkably increased by infusion of synthesized silver nanoparticles into the TiO2 photoanode. Rhodaminederivative RdS1 was synthesized by microwave-assisted condensation of hydrazide and 3-for-mylchromone. The synthesized silver nanoparticles were characterized with UV/Vis absorption spectroscopy and transmission electron microscopy. The interfacial charge transport phenomena of the dye-sensitized solar cell (DSSCs) are determined by electrochemical impedance spectroscopy and the corresponding efficiencies are calculated using current-voltage (I-V) curve. The solar cell photoanode with silver nanoparticles infused with RdS1 in titanium dioxide had the highest solar-to-electric power efficiency at 0.17%.

Spectroscopic (FTIR, 1H NMR) and SEM investigation of physicochemical structure changes of coal subjected to microwave-assisted oxidant stimulation

Owing to the sub-economic permeability, coalbed methane (CBM) reservoir usually requires stimulation. Novel CBM stimulation approaches have been proposed such as CO2 injection, liquid nitrogen frozen, microwave irradiation, high-voltage electrical pulse, and acid/oxidant treatment, but none is ubiquitously successful. Oxidant treatment targets the removal of organic micromolecules or minerals in coal, thereby etching pores and fractures. However, the oxidants exhibit low activity and permeation at ambient temperature. Oxidant corrosion also generates coal fines which can accumulate and jam in the fractures. Microwave heating may be a promising approach to overcome these limitations. This paper introduces the concept of using microwave-assisted oxidation for permeability enhancement. Fourier transform infrared spectroscopy (FTIR), 1H low-field nuclear magnetic resonance (1H NMR), and Scanning electron microscope (SEM) were used to assess the physicochemical structure changes of coal prior to and after stimulation. Results show that Microwave-assisted Fenton’s reagent and Na2S2O8 oxidation can break the self-associating hydrogen bonds in carboxyl, alcohol, and phenol, converting them into ether groups. The removal of oxygen-containing functional groups results in oligomerization and polymerization. Microwave-assisted condensation polymerization improves the maturation and aromaticity of coal. Microwave not only causes pore opening and expansion but also leads to pore collapse and closure. Oxidation not only induces dissolution, swelling, and breakage of coal but also soften the coal matrix, leading to a drop in the producible porosity. After microwave-assisted oxidation, the coal surface becomes porous with crisscrossed fractures. Combined with microwave fracturing, the oxidant is not reacting at the coal surface, but rather it is penetrating into the coal matrix and reacting internally. As a result, the NMR permeability of coal increases 471–1425%. This study reveals the potential of microwave-assisted oxidation to enhance coal permeability.

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.

Synthesis and Antimicrobial Activities of Some Polyphenol Compounds by Nano ZnO-TBAB as a Heterogeneous Catalytic Media

Introduction: Mannich reaction is a typical example of a three-component condensation reaction and the chemistry of Mannich bases has been the matter of search by researchers. Here, an efficient procedure for the synthesis of some new Mannich derivatives of simple phenols is described. Methods: In this procedure, a microwave-assisted and solventless condensation was done between different phenols, secondary amines and paraformaldehyde. The reactions proceeded in the presence of the catalytic amount of nano ZnO and tetrabutylammonium bromide (TBAB) in excellent yields. Ten new compounds were synthesized (A<sub>1</sub>-A<sub>10</sub>). Chemical structures of all new compounds were confirmed by different spectroscopic methods. We optimized the chemical reactions in different conditions. Optimization reactions were done in the presence of different mineral oxides, different amounts of TBAB and also different solvents. Nano ZnO and TBAB in catalytic amounts and solvent-free conditions were the best conditions. All the synthesized compounds were screened for their antimicrobial activities. Antifungal and antibacterial activities of the synthesized compounds were evaluated against some Candida species, filaments fungi, gram-positive and gram-negative bacteria by the broth microdilution method as recommended by CLSI. Results: The result showed that compounds A<sub>2</sub>, A<sub>3</sub> and A<sub>4</sub> against most of the tested Candida species and compounds A<sub>5</sub> and A<sub>7</sub> against C. parapsilosis and C. tropicalis exhibited considerable antifungal activities. Moreover, compounds A<sub>8</sub> and A<sub>10</sub> showed desirable antifungal activities against C. neoformance and C. parapsilosis, respectively. The antibacterial activities of the synthesized compounds were also evaluated. Compounds A<sub>6</sub> - A<sub>10</sub> against E. fecalis and compounds A<sub>5</sub>, A<sub>7</sub>, A<sub>9</sub> and A<sub>10</sub> against P. aeruginosa showed desirable antibacterial activities. Discussion: We have synthesized some new Mannich adducts of poly-hydroxyl phenols in the presence of nano- ZnO as a reusable catalyst, with the hope of discovering new lead compounds serving as potent antimicrobial agents. The advantages of this method are generality, high yields with short reaction times, simplicity, low cost and matching with green chemistry protocols. The antimicrobial studies of Mannich derivatives of phenols showed desirable results in vitro.

Microwave-assisted Synthesis of Novel Pyrazole Derivatives and their Biological Evaluation as Anti-Bacterial Agents.

Microwave-assisted condensation of acetophenone 1 and aromatic aldehydes 2 gave chalcone analogs 3, which were cyclized to pyrazole derivatives 6a-f via the reaction with hydrazine hydrate and oxalic acid in the presence of the catalytic amount of acetic acid in ethanol. The structural features of the synthesized compounds were characterized by melting point, FT-IR, 1H, 13C NMR and elemental analysis. The antibacterial activities of the synthesized pyrazoles were evaluated against three gram-positive bacteria, such as Enterococcus durans, Staphylococcus aureus, Bacillus subtilis and two gram-negative bacteria such as Escherichia coli and Salmonella typhimurium. All the synthesized pyrazoles showed relatively high antibacterial activity against S. aureus strain, and none of them demonstrated antibacterial activity against E. coli.

Microwave-assisted condensation of bio-based hydroxymethylfurfural and acetone over recyclable hydrotalcite-related materials

The microwave-assisted neat aldol condensation of biomass-derived platform chemical 5-hydroxymethyl furfural (HMF) and acetone over hydrotalcite-based catalysts has been studied. High conversions are obtained in very short times with relatively low catalyst loadings. The condensation products, which are biofuel and functional polymer precursors, are selectively obtained. Heterogeneous catalysts with different basic properties derived from the same parent hydrotalcite have been tested. The solids were characterized by PXRD, ICP-AES, ESEM-EDX, TEM, FT-IR and Raman spectroscopy, N2 physisorption, CO2 chemisorption and TGA-MS. The products in the final reaction mixtures were determined by GC-FID and -MS, HPLC-DAD and -TOF, and NMR. NMR was also used to determine the stereoconfiguration of the obtained products and pointed to a complete E-selectivity of our process. Different catalyst recycle strategies have been explored, and the most active catalyst, a meixnerite-type solid, can be recycled with low activity loss.

Microwave-Assisted Aldol Condensation of Furfural and Acetone over Mg–Al Hydrotalcite-Based Catalysts

The depletion of fossil fuel resources has prompted the scientific community to find renewable alternatives for the production of energy and chemicals. The products of the aldol condensation between bio-based furfural and acetone have been individuated as promising intermediates for the preparation of biofuels and polymeric materials. We developed a protocol for the microwave-assisted condensation of these two compounds over hydrotalcite-based materials. Mg:Al 2:1 hydrotalcite was prepared by co-precipitation; the obtained solid was calcined to afford the corresponding mixed metal oxide, which was then rehydrated to obtain a meixnerite-type material. The prepared solids were characterized by PXRD, ICP-AES, TGA-DSC and N2 physisorption, and tested as catalysts in the aldol condensation of acetone and furfural in a microwave reactor. The performance of the catalysts was assessed and compared; the meixnerite catalyst proved to be the most active, followed by the mixed metal oxide and the as-synthesized hydrotalcite, which has often been reported to be inactive. In all cases, the reaction is quite fast and selective, which makes our protocol useful for rapidly converting furfural and acetone into their condensation products.

Synthesis of hydrophobically modified guar gum film for packaging materials

Guar gum was hydrophobically modified by microwave assisted condensation with dimer acid (DA, a dimer of ricinoleic acid derived from castor oil) under “green” conditions. The condensation product (HMG) was then blended with polyvinyl alcohol and cast into films abbreviated as HMGF (hydrophobically modified guar gum film). FTIR and UV–visible spectroscopies, X-ray diffractometry, swelling, permeability and tensile strength measurements were used to evaluate the properties of HMG and HMGF. HMGF exhibits optimal mechanical strength with UV protective effect and restricted entry of chemical contaminants. HMGF could be easily disposed by burying in soil. HMGF may be a potential eco-friendly food packaging material.

Ultrafast Condensation of Carbon Nitride on Electrodes with Exceptional Boosted Photocurrent and Electrochemiluminescence.

Semiconducting polymeric carbon nitride (CN) has drawn wide attention ranging from photocatalysis to more recent biosensing owing to unique defect-tolerated optoelectronic properties and being metal-free, cheap, and highly stable. However, at the core of electrical-optical interconversion, the preparation of the CN photoelectrode is still challenging. Now, the growth of CN on electrodes is achieved simply by microwave-assisted condensation in seconds. The ultrafast heating not only addressed the thermodynamic contradiction of precursor volatilization during polymerization but also led to strongly adhesive CN layer on electrodes with gradient carbon-rich texture, greatly accelerating the electron-hole separation and mobility. Consequently, the CN photoelectrode exhibited a remarkable photocurrent and a record cathodic efficiency of electrochemiluminescence up to 7 times that of benchmark Ru(bpy)3 Cl2 in aqueous solution.

Hydrophilic Fluorescent Nanoprodrug of Paclitaxel for Glioblastoma Chemotherapy.

Highly water-soluble, nontoxic organic nanoparticles on which paclitaxel (PTX), a hydrophobic anticancer drug, has been covalently bound via an ester linkage (4.5% of total weight) have been prepared for the treatment of glioblastoma. These soft fluorescent organic nanoparticles (FONPs), obtained from citric acid and diethylenetriamine by microwave-assisted condensation, show suitable size (Ø = 17–30 nm), remarkable solubility in water, softness as well as strong blue fluorescence in an aqueous environment that are fully retained in cell culture medium. Moreover, these FONPs were demonstrated to show in vitro safety and preferential internalization in glioblastoma cells through caveolin/lipid raft-mediated endocytosis. The PTX-conjugated FONPs retain excellent solubility in water and remain stable in water (no leaching), while they showed anticancer activity against glioblastoma cells in two-dimensional and three-dimensional culture. PTX-specific effects on microtubules reveal that PTX is intracellularly released from the nanocarriers in its active form, in relation with an intracellular-promoted lysis of the ester linkage. As such, these hydrophilic prodrug formulations hold major promise as biocompatible nanotools for drug delivery.

Microwave-Assisted Solvent-Free Rapid Synthesis of 4-Methyl Coumarin Derivatives by Using Silica functionalized-SO3H as an Effective Heterogeneous Catalyst

A novel silica gel functionalized-SO3H as a heterogeneous catalyst was prepared and characterized by FT-IR, XRD, TGA and elemental analysis. It has been studied for microwave-assisted solvent-free Pechmann condensation. The result revealed that 20% w/w silica bonded 3-mercapto propyl diethylene diamine N-sulfamic acid (SMPDDSA) was found to be effective. 4-methyl coumarin derivatives were the only product obtained in good to excellent yield (75–94%). The present protocol accomplishes the reaction in much lesser time as compared to the conventional method.

Green Synthetic Approach and Antimicrobial Evaluation for Some Novel Pyridyl Benzoate Derivatives

Two series of substituted pyridyl 4-chlorobenzoates have been synthesized by microwave-assisted condensation of the corresponding 2-oxo-1,2-dihydropyridine-3-carbonitriles with 4-chlorobenzoyl chloride under solvent-free conditions. Alternatively, some compounds have also been prepared by conventional heating in methylene chloride in the presence of triethylamine. The structure of the synthesized compounds has been confirmed by spectral data (FTIR, 1D and 2D NMR). The new pyridyl benzoates were evaluated for antibacterial activity against gram-negative and gram-positive bacteria. The activity of 3-cyano-5-[(4-hydroxyphenyl)diazenyl]-4-methyl-6-phenylpyridin-2-yl 4-chlorobenzoate against gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) was comparable to that of amikacin used as standard antibiotic.

Nitrogen Amelioration-Driven Carbon Dioxide Capture by Nanoporous Polytriazine.

Nitrogen-enriched nanoporous polytriazines (NENPs) have been synthesized by ultrafast microwave-assisted condensation of melamine and cyanuric chloride. The experimental conditions have been optimized to tune the textural properties by synthesizing materials at different times, temperatures, microwave powers, and solvent contents. The maximum specific surface area (SABET) of 840 m2 g-1 was estimated in the sample (NENP-1) synthesized at 140 °C with a microwave power of 400 W and reaction time of 30 min. One of the major objectives of achieving a large nitrogen content as high as 52 wt % in the framework was realized. As predicted, the nitrogen amelioration has benefitted the application by capturing a very good amount of CO2 of 22.9 wt % at 273 K and 1 bar. Moreover, the CO2 storage capacity per unit specific surface area (per m2 g-1) is highest among the reported nanoporous organic frameworks. The interaction of the CO2 molecules with the polytriazine framework was theoretically investigated by using density functional theory. The experimental CO2 capture capacity was validated from the outcome of the theoretical calculations. The superior CO2 capture capability along with the theoretical investigation not only makes the nanoporous NENPs superior adsorbents for the energy and environmental applications but also provides a significant insight into the fundamental understanding of the interaction of CO2 molecules with the amine functionalities of the nanoporous frameworks.

Synthesis and antimicrobial evaluation of new glucosylimino thiazole derivatives

p-Sulphonic-N-propionyl aniline 3 was produced from sulphanilic acid with propionic acid under reflux for 2 h, then the compound 3 reacted with thionyl chloride and the corresponding imidoyl chloride 4 was obtained. When imidoyl chloride 4 reacted with potassium isothiocyanate and aniline, the corresponding thiourea derivatives 6 was produced. Compound 6 was reacted with tricyanovinylamine to produce the thiazole derivative 7 after cyclization. The microwave-assisted condensation of 2,3,4.6,-tetra-O-acetyl-β-D-glucopyranosylisothiocynate 8 with thiazole derivative 7 afforded the thiourea derivatives 9. Compound 10 a, b has been synthesized by reacting thiourea derivatives 9 with chloroacetone. The prepared compounds were screened for antibacterial properties against Staphylococcus aureus and Escherichia coli, and antifungal activity against Candida sp. The structure assignments of the new synthesized compounds are based on spectroscopic data.

MICROWAVE ASSISTED SYNTHESIS, SPECTRAL CORRELATION AND ANTIMICROBIAL EVALUATION OF SOME ARYL IMINES

A series of aryl imines have been synthesized by SiO2-H3PO4 catalyzed microwave assisted condensation of amine and aldehyde under solvent-free conditions. The yield of the imines has been found to be more than 80%. The purity of all imines has been checked using their physical constants and spectral data as published earlier in literature. The UV λmax(nm), infrared νC=N(cm-1), NMR δ(ppm) of C-H and C=N spectral data have been correlated with Hammett substituent constants and F and R parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effect of substituents on the above spectral data has been studied. The antimicrobial activities of all imines have been studied using Bauer-Kirby method.

N‐rich Porous Organic Polymer as Heterogeneous Organocatalyst for the One‐Pot Synthesis of Polyhydroquinoline Derivatives through the Hantzsch Condensation Reaction

AbstractIncorporation of nitrogen functionality onto the high surface area porous polymeric network are very demanding in designing suitable heterogeneous organocatalyst having surface basicity. Here we report the synthesis of a new N‐rich triazine based microporous organic polymer (TrzMOP) through a simple and efficient condensation pathway involving the reaction between 1,4‐bis(4,6‐diamino‐s‐triazin‐2‐yl)‐benzene (SL‐1) and 2,5‐thiophene dicarboxaldehyde. The material has been characterized by using powder XRD, FTIR spectroscopy, solid state magic‐angle spinning 13C NMR, CHN analysis, FESEM, HRTEM, CO2‐TPD and N2 adsorption/desorption techniques. This nitrogen‐rich new porous organic polymer showed very high catalytic efficiency for one‐pot proficient synthesis of polyhydroquinoline derivatives via microwave assisted condensation reaction. As little as 8 mg of catalyst was found to be effective under the optimum reaction conditions. In addition, TrzMOP catalyzed synthesis of biologically active polyhydroquinoline derivatives are very cost effective, scalable, less time consuming, and environmentally benign compared to those of currently used as heterogeneous catalysts.

Degradable Thermosets Derived from an Isosorbide/Succinic Anhydride Monomer and Glycerol

Isosorbide is a renewable chemical of considerable interest as a monomer and monomer precursor due to its potential use in replacements for fossil-fuel derived polymers. In the present study, a facile microwave-assisted condensation of isosorbide with succinic anhydride was developed that dramatically reduced the reaction time. The resulting isosorbide disuccinic acid derivative (I-S-2) was polymerized under solvent-free conditions with glycerol to produce a renewable, cross-linked polyester with high modulus and appreciable thermal stability. Inclusion of 13 wt % or more of low molar mass hydroxy-telechelic poly(ethylene oxide) (PEO) (Mn = 300 g/mol) produced materials with a notable decrease in modulus and glass transition temperature. Degradation studies at 50 °C in acidic and basic solutions demonstrated the ability of the I-S-2 thermosets to be readily hydrolyzable. Furthermore, the resulting aqueous degradation solutions can be concentrated and reheated to produce new materials, albeit with a reduct...

Studies on free radical scavenging, cancer cell antiproliferation, and calf thymus DNA interaction of Schiff bases

Thirty-nine Schiff bases were synthesized by performing microwave-assisted condensation of the corresponding aldehydes and aromatic amines. Their reactive nitrogen species (RNS) scavenging activity and inhibitory effects against cancer cell growth were then subsequently investigated. Additionally, the interaction between the calf thymus DNA (ctDNA) and selected Schiff bases was evaluated using fluorescence spectroscopy, and their binding parameters were determined. The yields of the various compounds ranged from moderate to excellent (43–99%) after only a 2-min reaction. The hydroxylated Schiff bases 2, 8, 15, 16, 18, 20, 29, 32, 34, and 37 were found to be potent scavengers of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals with half-maximal scavenging concentration (SC50) values lower than that of the positive control, resveratrol. The presence of hydroxyl substituents on the aromatic rings also proved essential to the cytotoxicity of the compounds. The binding constants (Kb) obtained using fluorescence spectroscopy ranged from 0.37 to 3.07×105Lmol−1, and were strongly influenced by the structure and hydroxylation degree. Schiff bases 3 and 8 showed promising cytotoxic activity, with half-maximal growth inhibitory (GI50) values in the same order of magnitude as those exhibited by the reference drug, doxorubicin against various cell lines. Interestingly, these compounds also showed the highest Kb, suggesting that the cytotoxic activity could be related to their interaction with the DNA of the tumor cells. The results of this study highlighted some Schiff bases as potential lead compounds for the design of new free radical scavengers and anticancer agents.