One‐pot‐one‐step,microwave‐assisted Fischer indole synthesis

The Fischer indole synthesis was carried out using microwaves instead of conventional heating procedures. When the mixture of phenylhydrazine, cyclohexanone and zinc chloride was irradiated at 600 W for 3 min, 76% of 1,2,3,4‐tetrahydrocarbazole was obtained. However, when zinc chloride was replaced with p‐toluenesulfonic acid (p‐TSA), the reaction yielded 91% of 1,2,3,4‐tetrahydrocarbazole. Thus, a series of indoles were prepared using microwaves in the presence of p‐TSA catalyst. J. Heterocyclic Chem., (2011).     

Polystyrene-Supported Palladium (Pd@PS)-Catalyzed Carbonylative Annulation of Aryl Iodides Using Oxalic Acid as a Sustainable CO Source for the Synthesis of 2-Aryl Quinazolinones

An efficient and convenient strategy for the synthesis of diversely substituted quinazolinones from o-carbamoyl/cyano aniline and aryl iodides using oxalic acid as a CO source under polystyrene supported palladium (Pd@PS) nanoparticles (NPs) catalyzed conditions has been developed. In this study, oxalic acid has been employed as safe, economic, environmentally benign, sustainable and bench-stable, solid CO surrogate under Double-Layer-Vial (DLV) system for the synthesis of 2-aryl quinazolinones. This methodology does not require any special high-pressure equipment like autoclaves, microwaves, etc. Moreover, a simple procedure for catalyst preparation, catalyst recyclability, easy handling of reaction, additive and base-free generation of CO, excellent to good yields and vast substrate scope are the additional features of developed protocol.     

Adhesion of molded polyethylene using polyethylene gels by microwave heating

Adhesive effect of polyethylene gels on the molded polyethylene by heating with microwaves has been investigated. Polyethylene gels in polar organic solvents such aso-xylene, chlorobenzene,o-dichlorobenzene,m-dichlorobenzene, 1,1,1,2-tetrachloroethane, and 1,1,2,2-tetrachloroethane were used as adhesives. All of these gels showed adhesive effect when heated with microwaves. In particular, the gels in 1,1,2,2-tetrachloroethane showed such strong adhesion that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking by heating for 8 min in a 500 W (2450 MHz) microwave oven.     

Solvent‐free cycloaddition reaction of 3‐indolylimines with chloroacetyl chloride under microwave irradiation

Solvent‐free approach is developed for the rapid synthesis of spiro[azetidine‐indoles] 6a–g on basic alumina supported potassium carbonate (K₂CO₃–Al₂O₃) from the cycloaddition reaction of indolylimines 3 and chloroacetyl chloride 4 as synthons using microwaves. The procedure neither required toxic and hazardous base nor volatile solvents. 3 was synthesized in situ by the neat reaction of indole‐2,3‐diones 1 and fluorinated anilines 2 under microwave irradiation. Solvent‐free aminoalkylation of spiro compounds 6a and 6b has been carried out under microwaves. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:468–473, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10180     

Green Procedure for the Synthesis of Phthalazino[2,3‐b]phthalazine‐5,7,12,14‐tetraones

Different novel phthalazino[2,3‐b]phthalazine‐5,7,12,14‐tetraones were synthesized in a simple and environmentally benign method from the reaction of phthalic anhydrides with semicarbazide or thiosemicarbazide using montmorillonite K‐10 clay as solid heterogeneous acidic catalyst and microwaves under solvent‐free conditions in good yields and short reaction times. Products were characterized by the elemental analysis, IR, NMR, and mass spectrometry.     

Rapid and Efficient Microwave‐Assisted Synthesis of Some New Triazol‐3‐one Derivatives

A growing body of literature has shown the effectiveness of using microwaves in chemical reactions. The aim of this study is to demonstrate a rapid and highly efficient synthesis of some new triazol‐3‐ones via microwave heating using a monomode microwave. Compared with the thermal process, the microwave heating induces a dramatic reduction of the reaction time and improvement of the yields. In this study, rapid N‐benzylation and N‐acetylation of triazol‐3‐ones were achieved by microwave irradiation method for the first time. The newly synthesized compounds showed moderate antimicrobial activity against the standard bacterial and fungal organisms tested.     

In Search of the Driving Factor for the Microwave Curing of Epoxy Adhesives and for the Protection of the Base Substrate against Thermal Damage

This study used controlled microwaves to elucidate the response of adhesive components to microwaves and examined the advantages of microwave radiation in curing epoxy adhesives. Curing of adhesives with microwaves proceeded very rapidly, even though each component of the adhesive was not efficiently heated by the microwaves. The reason the adhesive cured rapidly is that microwave heating was enhanced by the electrically charged (ionic) intermediates produced by the curing reaction. In contrast, the cured adhesive displayed lower microwave absorption and lower heating efficiency, suggesting that the cured adhesive stopped heating even if it continued to be exposed to microwaves. This is a definite advantage in the curing of adhesives with microwaves, as, for example, adhesives dropped onto polystyrene could be cured using microwave heating without degrading the polystyrene base substrate.     

Microwave Assisted Deprotection of N , N -Dimethylhydrazones in Water Using Palladium Chloride–Tin Chloride as Catalyst

 N,N-Dimethylhydrazones of ketones and aldehydes undergo facile cleavage to the corresponding carbonyl compounds upon exposure to microwaves in water containing a catalytic amount of PdCl₂–SnCl₂ in high yields.     

Microwave-assisted aqueous phase synthesis and single crystal study of oxovanadium(IV) (2-hydroxybenzylideneamino) acetate

Single crystal of oxovanadium(IV) (2-hydroxybenzylideneamino) acetate was synthesized by template method in aqueous phase using microwaves as the source of energy. A fine crystalline complex was obtained in high yield within a few minutes. All bond distances and angles were observed to study the effect of bonding of vanadium and distortion from normal. Other spectroscopic data are also reported.     

Synthesis of 1‐H‐1,5‐benzodiazepines derivatives using SiO2/ZnCl2

A general and easy method for the synthesis of several 1‐H‐1,5‐benzodiazepines using SiO₂/ZnCl₂ under solvent‐free conditions is described. This efficient and improved method furnishes selectively and in good yields the corresponding 1‐H‐1,5‐benzodiazepines derivatives starting from o‐phenylenediamine and cyclic or acyclic ketones. The catalytic system was reused up four times, and the use of focused microwaves accelerates the reaction. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:180–185, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20674     

Microwave Assisted Deprotection of N,N-Dimethylhydrazones in Water Using Palladium Chloride–Tin Chloride as Catalyst

Summary.  N,N-Dimethylhydrazones of ketones and aldehydes undergo facile cleavage to the corresponding carbonyl compounds upon exposure to microwaves in water containing a catalytic amount of PdCl₂–SnCl₂ in high yields. Corresponding authors. E-mail: rahman@umz.ac.ir Received December 27, 2001. Accepted (revised) February 6, 2002     

Fast analysis of volatile components of Achillea tenuifolia Lam with microwave distillation followed by headspace single-drop microextraction coupled to gas chromatography-mass spectrometry (GC–MS)

This article investigates the effect of microwaves on the amount of volatile compounds Achillea tenuifolia Lam with two methods, headspace single-drop microextraction and microwave-assisted headspace single-drop microextraction (MA-SDME), for the analysis of essential oil. Solvent selection, solvent volume, microwave power, irradiation time and sample mass were optimised by the simplex method.     

A ‘one pot’ synthesis of 2‐aryl‐4H‐1‐benzopyran‐4‐ones under coupled microwave phase transfer catalysis (PTC) and ultrasonic irradiation PTC

A ‘one pot’ synthesis of 2‐aryl‐4H‐1‐benzopyran‐4‐ones (3a‐3f) is being reported. A mixture of o‐hydroxyacetophenone, aroyl chloride, powdered n‐tetrabutylammonium hydrogensulphate (n‐TBAHSO₄) and potassium hydroxide (KOH) were either irradiated by microwaves or sonicated in an ultrasonic cleaning bath to afford flavones directly. On the contrary, conventional liquid‐liquid Phase Transfer Catalysis (PTC) using benzene as organic phase and aqueous KOH as the second phase afforded first β‐diketones in accordance with Baker‐Venkataraman synthesis which upon cyclization by p‐toluenesulphonic acid (p‐TSA) gave desired flavones in the next step. PTC coupled with microwaves or ultrasound show enhanced yields, the clean reaction conditions require less time, and have easier workup protocol. All synthesized compounds were characterized by their Proton Magnetic Resonance (PMR), IR, FAB Mass and elemental analyses.     

Influence of microwave irradiation on enzyme kinetics

The in vitro effect of 2.45 GHz microwave irradiation on porcine pepsin activity under controlled temperature and absorbed microwave power via kinetic parameters was evaluated. Kinetic study with respect of time of irradiation demonstrated the existence of an inactivation effect of microwaves at pH 2 on pepsin molecule. Bovine serum albumin (BSA)-bromphenol blue (BPB) complex was used as substrate for the assay of pepsin by kinetic method. Depending on absorbed microwave dose, the degree of caused inactivation varies from 39.11 to 45.91% for 5 and 20 min of pepsin MW irradiation, respectively. The V _maxapp and K _mapp were calculated for low (5 min of MW irradiation) and higher specific absorbed dose (20 min of MW irradiation), as well as for untreated enzyme, from double reciprocal Lineweaver-Burk plot. The effect of microwaves on substrate (BSA-BPB complex) was also investigated. For reaction performed with MW irradiated substrate for 5 min the reaction rate was decreased for 15.15%, while for 20 min of substrate irradiation reaction rate was decreased for 25.52% compared to the control reaction. The article is published in the original.     

The impact of microwave energy on the results of silica gel hydrothermal modification

Two series of the hydrothermally treated (HTT) silica gel samples using the microwave reactor or the classical autoclave have been prepared. The HTT modification processes have been performed under the liquid water layer or in the water vapour. The initial and HTT silica samples were examined by means of adsorption (N₂), thermogravimetric (TG) and infra red (FTIR-ATR) methods. On the basis of the obtained results it was stated that even a short time of HTT modification using microwaves is enough to make distinct changes in the porous structure of silica. The time and pressure are the most influential parameters during HTT using microwaves. However, in the case of the samples modified in the classical autoclave the most important factors are temperature and time. The hydrothermally modified silica samples possess different concentration of intraglobular water dependently on applied treatment conditions and water state.     

Microwave and Ultrasound Irradiation‐Assisted Synthesis of Novel Disaccharide‐Derived Arylsulfonyl Thiosemicarbazides

The synthesis of 1‐arylsulfonyl‐4‐(1′‐N‐hepta‐O‐acetyl‐β‐lactosyl)thiosemicarbazides by reaction of hepta‐O‐acetyl‐α‐D‐lactosyl isothiocyanate with substituted phenylsulfonyl hydrazines has been shown to occur in less than 1 min under microwave activation and 8 min under ultrasound irradiation at room temperature. It is noteworthy that when ultrasound and microwaves (MW) were utilized, a cleaner reaction accompanied with higher yields was observed.     

Characterization and study of microwave activation effects on the polystyrene tacticity

¹³C Nuclear magnetic resonance proved to be an advantageous tool to determine the stereoregularity of polystyrene polymers. The latter was achieved through the analysis of the signal of the quaternary carbon and that of the carbon-p in the aromatic ring too. Styrene was polymerized through microwaves and conventional heating activation using two different polymerization techniques: emulsion and bulk. Microwave activation was performed in a mono-modal type device under the following experimental conditions: various initiator concentrations, an average irradiation power of 50?W, temperature of 70°C, and using a batch reactor for emulsion and bulk experiments. The results obtained in these experiments were compared with those obtained by conventional heating activation polymerization under the same initiator concentration and temperature conditions. Microwave-activated reactions resulted in shorter reaction times and higher yields. The tacticity of the polymer samples was not significantly altered, which lead to the conclusion that, in this case, the stereoregularity of polystyrene was not influenced by microwave irradiation.     

Synthesis of some aromatic aldehydes and acids by sodium ferrate in presence of copper nano‐particles adsorbed on K 10 montmorillonite using microwave irradiation

Excellent yields were obtained in the oxidation of benzyl alcohol, benzaldehyde, 4‐methoxy benzyl alcohol and 4‐nitro benzaldehyde with sodium ferrate in the presence of copper nano particles adsorbed on montmorillonite K 10 under microwave irradiation. Aniline, p‐toluidine, phenol, catechol, resorcinol and p‐cresol polymerize under these conditions without exposing the mixture to microwaves. The one‐pot system does not require tedious separation of ferrate and is quick and environmentally benign. Copyright © 2007 John Wiley & Sons, Ltd.     

Microwave activation of catalytic transformation of t-butylphenols

Kinetics of catalytic transformation of 2- and 4-t-butylphenol (2TBP and 4TBP) in the liquid phase on a heterogeneous KSF catalyst has been studied in detail under conventional and microwave conditions. The process includes dealkylation, isomerization and transalkylation reactions. Its kinetics has been described using the method of initial reaction rates. It was found that microwaves affect both the reaction rate and the selectivity. The results were explained in terms of “microwave-induced polarisation” assuming an interaction of microwaves with a highly polarised reagent molecule in adsorbed state on the acidic active site. Temperature and solvent effects were also examined. The reaction mechanism of t-butylphenol transformation is discussed on the basis of electrophilic aromatic substitution via bimolecular reactions.     

Selective Iodination of Benzylic Alcohols with KI/H2SO4 Supported on Natural Kaolinitic Clay Under Microwave Irradiation

 Benzylic alcohols are selectively converted into their corresponding iodides using KI/H₂SO₄ supported on natural kaolinitic clay and microwaves.