Employing Microwave Irradiation Research Articles

Kinetic Products Under Thermal Conditions: Rapid Entry into α/β-D-Galactofuranosides Using Microwave Irradiation and Selective Lewis Acids

A modified Fischer-Lubineau reaction, employing microwave irradiation and selected Lewis acids such as Mn(ClO4)2, Mn(C2H3O2)3, FeCl3, CoCl2, and AgF as independent additives, induces rapid entry into α/β-d-galactofuranosides in very good yield and purity.

An Efficient and Rapid Synthesis of 2-amino-4-arylthiazoles Employing Microwave Irradiation in Water

A facile, high yielding green chemical synthetic protocol adaptable to the parallel synthesis of a library of potentially bioactive 2-amino-4-arylthiazoles is reported herein. The methodology involves the condensation of various aracyl bromides with N-arylthioureas under MWI using water as solvent, to yield pure products (81%-97%) in very short reaction times (1-20 min).

Effect of Microwave Power on the Physical Properties of Carboxylic Acid-Coated Manganese-Ion-Doped Zinc Sulfide Nanoparticles

Bright ZnS : Mn2+nanoparticles have been synthesized employing microwave irradiation technique and using zinc 2-ethylhexanoate as a novel zinc precursor. A series of samples is obtained by changing the microwave power (from 150 W to 500 W) to study its effect on the physical properties of the ZnS : Mn2+nanoparticles. The particle size increases with increasing microwave power for the samples synthesized in the microwave range of 150 W to 300 W. The decrease in particle size for higher microwave power (400 W and 500 W) can be described as an onset of the secondary nucleation due to the excess energy associated with the higher microwave power. The sample synthesized with microwave power of 300 W shows highest luminescence intensity suggesting increase in Mn2+luminescence center for the sample synthesized at 300 W, as supported by the quantity analysis results.

Rapid and efficient protic ionic liquid-mediated pinacol rearrangements under microwave irradiation

Several protic ionic liquids were tested as potential mediators for pinacol rearrangements employing microwave irradiation. Using hydrobenzoin as a model substrate, the optimal conditions were found to be heating at 80 °C for 5 min using H2SO4:triethylamine as the ionic liquid. A key feature of this reaction was to keep the microwave power low (20 W) to avoid ionic liquid degradation. Application of these conditions to triphenylethylene glycol gave rearrangement products in high yield and purity, while phenylethylene glycol and styrene oxide gave pinacol products that underwent a cascade aldol condensation. These conditions represent an efficient means by which pinacol rearrangements can be carried out while avoiding the use of strong Bronsted acids, high temperatures and extended reaction times.

Microwave-Assisted Synthesis of Some Novel Thiazolidinone and Thiohydantoin Derivatives of Isatins

A simple, rapid, and efficient method for the synthesis of some new thiazolidinone and thiohydantoin derivatives of isatins along with some Mannich bases has been achieved in excellent yield from indole-2,3-dione-3-thiosemicarbazone employing microwave irradiation.

Magnetite/graphene composites: microwave irradiation synthesis and enhanced cycling and rate performances for lithium ion batteries

By employing microwave irradiation as a heat source, magnetite/graphene composites were synthesized by depositing Fe3+ in the interspaces of graphene sheets. The Fe3O4 nanoparticles were dispersed on graphene sheets. As anode materials for lithium ion batteries, they showed high reversible capacities, as well as significantly enhanced cycling performances (about 650 mA h g−1 after 50 cycles) and high rate capabilities (350 mA h g−1 at 5 C). The enhancement could be attributed to graphene sheets, which served as electron conductors and buffers. Our results opened a new doorway for the application of graphene sheets to prepare anode materials of lithium ion batteries with superior performances.

The synthesis and characterization of metal-free and metallophthalocyanine polymers by microwave irradiation containing diazadithia macrocyclic moieties

A tetranitrile monomer was synthesized by nucleophilic aromatic substitution of N,N′-(2,2′-(propane-1,3-diylbis(sulfanediyl))bis(ethane-2,1-diyl))bis(4-methylbenzenesulfonamide) onto 4-nitrophthalonitrile. A metal-free phthalocyanine polymer was prepared by the reaction of the tetranitrile monomer under N 2 in the presence of 2-(dimethylamino)ethanol at 145 °C for 24 h. Zinc(II), copper(II), cobalt(II), nickel(II), lead(II), phthalocyanine polymers were prepared by reaction of the tetranitrile with the chlorides of zinc (II), copper (II), cobalt (II), nickel (II), lead (II), employing microwave irradiation in the presence 2-(dimethylamino)ethanol at 175 °C, 350 W for 10 min. The thermal stabilities of the phthalocyanine compounds were determined by thermogravimetric analysis. The new compounds were characterized by a combination of IR, 1H NMR, 13C NMR, UV–vis, elemental analysis and MS spectral data.

Chemoselective and Microwave-Assisted Synthesis of Glycopeptoids

The chemoselective glycosylation of N-alkylaminooxy side chains with unprotected reducing sugars has proven useful for the synthesis of glycopeptides. Herein, we extend the N-alkylaminooxy strategy to the synthesis of glycopeptoids. A N-methylaminooxy submonomer was efficiently synthesized and incorporated into peptoids. Glycosylation of the peptoids proceeded chemoselectively and site-specifically at the N-methylaminooxy moieties. Employing microwave irradiation significantly increased the degree of glycosylation and shortened the reaction times.

Reversed-phase high performance liquid chromatographic separation of diastereomers of β-amino alcohols and microwave assisted synthesis of Marfey's reagent, its chiral variants and diastereomers

Ten chiral derivatizing reagents (CDRs) were synthesized by replacing the l-Ala–NH 2 moiety in Marfey's reagent (MR) by seven l-amino acid amides and three l-amino acids employing microwave irradiation (MW) and were characterized. Ten racemic amino alcohols were derivatized with these CDRs under MW. The diastereomers were separated on a reversed-phase C 18 column using binary mixtures of acetonitrile with aqueous trifluoroacetic acid (TFA) and triethylammonium phosphate buffer (TEAP). In general, amino acid variants of MR provided better separation of diastereomers in comparison to amino acid amide variants. The method was also found successful for the separation of 20 diastereomers from a mixture.

Thermal Effects in the Organocatalytic Asymmetric α‐Amination of Disubstituted Aldehydes with Azodicarboxylates: A High‐Temperature Organocatalysis

AbstractThis article describes the thermally accelerated organocatalytic α‐amination of disubstituted aldehydes with azodicarboxylates under microwave conditions. Compared to the results previously obtained at room temperature, both yield and enantioselectivity could be significantly increased. Employing microwave irradiation resulted in a considerably reduced reaction time. Therefore, this improved protocol allows the fast and efficient synthesis of α,α‐disubstituted amino aldehydes and provided the best results for the α‐amination of disubstituted aldehydes to date. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Microwave‐assisted döbner synthesis of 2‐phenylquinoline‐4‐carboxylic acids and their antiparasitic activities

Abstractmagnified imageA series of twelve substituted 2‐phenylquinoline‐4‐carboxylic acids analogous to antimalarial and antileishmanial natural products was developed via the Döbner reaction employing microwave irradiation (MW). The products were obtained in moderate yields in 0.5‐3 minutes and nine of them were evaluated in vitro against the parasites responsible for malaria, leishmaniasis and trypanosomiasis diseases (WHO, Switzerland). Four compounds exhibited activity against Trypanosoma cruzi and another two resulted active against Plasmodium falciparum and Leishmania infantum, respectively.

Effect of microwave irradiation on surface characteristics and luminescent properties of BaMgAl 10O 17:Eu blue phosphor

BaMgAl 10O 17:Eu (BAM) has been an excellent blue-emitting phosphor due to its outstanding luminescence efficiency and purity for plasma display panels. An attempt of employing microwave irradiation to modify the surface properties including morphology and crystallinity of BAM powder was performed in this work. X-ray powder diffraction (XRD) analysis and scanning electron microscopy (SEM) images show that the blue-emitting phosphors after microwave irradiation treatment exhibit better crystallinity and smoother surface. Furthermore, the vacuum ultraviolet photoluminescence spectra show that the luminescent intensity of BAM phosphors can be effectively enhanced by a factor of six times under microwave irradiation treatment. The enhanced luminescent properties can be closely related to the surface modification and reduced defects of the BAM blue-emitting phosphors.

Microwave‐Assisted Solvent‐Free Synthesis of Substituted 2‐Quinolones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Microwave accelerated S N2′ substitution of Baylis–Hillman acetates: A comparative study of conventional heating versus microwave irradiation

Baylis–Hillman acetates undergo a rapid S N2′ allylic substitution with ethyl (triphenyl phosphoranylidene) acetate under microwave irradiation to afford ethyl 5-aryl or alkyl-( E)-pent-4-enoates in high yields with high ( E)-stereoselectivity. The reaction rates and yields are significantly improved by employing microwave irradiation. A comparative study under thermal conditions and microwave irradiation is also described.

Convenient Preparation of Pyrano Benzopyranes in Aqueous Media.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Microwave-assisted solvent-free synthesis of substituted 2-quinolones

A rapid and efficient method for the preparation of a variety of substituted 2-quinolones has been developed through the reactions of o-aminoarylketones with ester compounds containing a reactive α-methylene moiety in the presence of a catalytic amount of cerium chloride heptahydrate under solvent-free conditions in high yields. The rate and yield of the reaction are considerably improved by employing microwave irradiation.

Rat Neuropeptidomics by LC−MS/MS and MALDI−FTMS: Enhanced Dissection and Extraction Techniques Coupled with 2D RP-RP HPLC

Recently developed sample preparation techniques employing microwave irradiation have enabled the comprehensive study of endogenous mammalian neuropeptides. These methods reduce interference from post-mortem protein degradation by deactivating proteases via heat denaturation. Alternatively, we have developed a protocol using cryostat dissection and a boiling extraction buffer to achieve a similar effect. This novel methodology greatly reduces post-mortem protein contamination and increases neuropeptide identification without the use of specialized equipment. In addition, a 2D HPLC scheme employing differential pH selectivity in the first and second dimensions has been used to enhance neuropeptidome coverage. By using our novel dissection protocol in tandem with 2D RP-RP HPLC, we were able to identify a total of 56 peptides from known neuropeptide precursors, including 17 previously unidentified peptides. The use of cryostat dissection and two-dimensional RP-RP HPLC enhances the detection of novel neuropeptides by deactivating proteases and reducing sample complexity.

Microwave-assisted Friedländer synthesis of quinolines derivatives as potential antiparasitic agents

A series of substituted quinolines was developed via the Friedländer reaction employing microwave irradiation (MW), in the presence of a catalytic amount of hydrochloric acid. The products were obtained in good yields in 1.5–12 min and were tested in vitro against the parasites causative of malaria, leishmaniasis, sleeping sickness and Chagas’ disease (TDR, WHO). Some of these compounds exhibited activity against Plasmodium falciparum and others resulted moderately active against Trypanosoma cruzi.

Convenient Preparation of Pyrano Benzopyranes in Aqueous Media

The three‐component reaction of aldehyde, malononitrile, and 4‐hydroxy coumarin has been efficiently performed in aqueous K2CO3 using a simple, clean, environmentally benign, novel procedure employing microwave irradiation. The observed yields and enhancement in reaction rates can be attributed to the uniform heating effect of microwave. The microwave‐accelerated reaction technique not only eliminates the use of external base and organic solvents but also requires only water in both the reaction step and workup, thus rendering the whole procedure into a truly ecofriendly protocol.

Palladium-Catalyzed Cross-Coupling of Aryl Triethylammonium Bis(catechol) Silicates with Aryl Bromides Using Microwave Irradiation

The scope of the palladium-catalyzed cross-coupling reaction of aryl bis(catechol) silicates has been extended to include the coupling of aryl bromides by employing microwave irradiation. This new set of coupling conditions is tolerant of electron-rich and -deficient aryl bromides. In addition, a variety of substituted aryl bis(catechol) silicates have been successfully cross-coupled.