Sharif Digital Repository

The magnetoresistance of single phase polycrystalline Gd(Ba 2-xPrx)Cu3O7-δ samples have been studied within thermally activated flux creep model. The decrease of pinning energy with applied magnetic field can be scaled to two power law relations for magnetic fields, smaller and also larger than about 1 kOe. The derived pinning energy shows that the Pr-doping, similar to weak links, decreases the vortex flux pinning energy. It is also concluded that the substitution of Pr at Ba site has a more destructive effect on the flux dynamics than Pr at rare earth site. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim  

The method of unity bond index-quadratic exponential potential (UBI-QEP) is employed to derive the energetic parameters associated with the steps of the pathway which we propose for the catalytic decomposition of azomethane on the Pd(111) surface. According to the energy calculations, azomethane adsorbs molecularly in trans-configuration and then decomposes to CH3N with no activation energy. The reaction continues by tilting and dehydrogenation to the products (H2 and HCN). The calculated activation energies at various surface coverages perfectly account for the variation of relative yields of H2 and HCN with changing of the coverage of azomethane. According to the calculations, desorption... 

Statistical models for the study of solvent effects on the endo/exo selectivity of Diels-Alder reactions using molecular surface electrostatic potentials was obtained. The models show that hydrogen bond interactions of solvent molecules favor the predominance of the endo isomer for the reaction of methyl acrylate, methyl methacrylate and methyl trans-crotonate with cyclopentadiene whereas the effect of solvophobicity seems to be negligible. © 2003 Published by Elsevier Ltd  

In situ prepared iminium salts are very effective electrophiles in Baylis-Hillman reactions and react with methyl acrylate in the presence of a catalytic amount of a tertiary amine at ambient temperatures to afford the corresponding Baylis-Hillman adducts. The product undergoes conjugated addition with (trimethylsilyl)dialkylamines to give the diamine 5 in good yields. © 2002 Elsevier Science Ltd. All rights reserved  

A one-pot, three-component, Mannich reaction of electron-rich aromatic compounds with in situ prepared iminium salts in 5 M ethereal lithium perchlorate gives good yields of aminoalkylated products at room temperature. © 2001 Elsevier Science Ltd. All rights reserved  

Aldehydes and aryl alkyl ketones were efficiently transformed to thioamides with the same number of carbon atoms via Willgerodt-Kindler reaction under microwave irradiation in solvent-free conditions. The thioamides obtained were hydrolyzed to corresponding carboxylic acids with microwave dielectric heating in one minute. Both reactions are very fast and the yields are excellent  

The LiClO4-mediated one-pot reaction of aldehydes with (trimethylsilyl)dialkyl amines and the lithium salt of sulfoxides or sulfones, affords the corresponding β-(dialkylamino) sulfoxides and β- (dialkylamino) sulfones in high yields. The aminosulfoxidation reaction of aliphatic or aromatic aldehydes lacks diastereoselectivity, but the diastereomeric sulfoxides can be separated by HPLC or column chromatography for further use  

An operationally simple and entirely green protocol for heteropoly acid catalyst conjugate addition of indoles and pyrrole to unsaturated carbonyl compounds and nitro-alkene in water was investigated. It is important that the products arising from 1,2-addition were not observed under the reaction conditions. Pyrroles also readily underwent Michael addition at Α-positions under the same reaction conditions. Indole and many of its derivatives are present in many substances commonly found in nature. Micheal addition reactions are performed in organic solvents with the reactions in water are relatively scarce. The Michael addition between indole and methyl vinyl ketone in the presence of... 

Reaction of aromatic α-bromoketones, sodium azide and aromatic or aliphatic terminal acetylenes in the presence of Cu/Cu(OTf)2following the classical method (aqueous acetonitrile at room temperature) and under microwave irradiation (H2O at 85 °C) leads to 1,4-disubstituted 1,2,3-triazoles as the final products after simple filtration  

Originally, application of nano zero valent iron (nZVI) particles for the removal of lead (Pb2+) in porous media was studied. At first, stabilized nZVI (S-nZVI) was prepared and characterized, then used in batch and continuous systems. Based on the batch experiments, corresponding reaction kinetics well fitted with the pseudo-first-order adsorption model, and reaction rate ranged from 0.01 to 0.04 g/mg/min depend on solution pH and the molar ratio between Fe and Pb. In batch tests, optimal condition with more than 90% removal efficiency at 60 min was observed at a pH range of 4 to 6 and Fe/Pb ratio more than 2.5. Continuous experiments exposed that Pb2+ remediation was as well influenced by... 

The existence of structure for ionizing fast-strong and fast-weak detonation waves in magnetohydrodynamics are proved. The reactions are assumed to be one step exothermic reactions with a natural discontinuous reaction rate function. The problem is studied for a general gas, considering some general thermodynamics rules which described by a fairly mild set of hypotheses. The uniqueness and nonuniqueness of structure are also considered. © 2007 Elsevier Ltd. All rights reserved  

Copper(II) efficiently catalyzes the aerobic oxidation of aryl thioacetamides into the corresponding α-keto aryl thioamides in moderate to high yields in the presence of K2CO3 under O 2 atmosphere. This protocol is simple, clean, and generates water as the only byproduct. A mechanism is proposed for the reaction course. © Georg Thieme Verlag Stuttgart  

A convenient one-pot multi-component reaction of aromatic aldehydes, enolizable ketones or β-keto esters and acetonitrile in the presence of acetyl chloride and 10 mol% ZnO nanoparticles for the synthesis of β-acetamido ketones/esters at room temperature is described. © 2007 Elsevier B.V. All rights reserved  

The mechanism and kinetics of the hydrogen evolution reaction (HER) on tin electrode in 0.1 M H2SO4 solution were studied using the methods of steady-state polarization and electrochemical impedance spectroscopy. The simulation of the data obtained from these two methods, using nonlinear fitting procedure allowed us to determine the rate constants of Volmer, Heyrovsky and Tafel steps associated with the mentioned reaction. The kinetic results indicate that HER mechanism at low negative potentials is a serial combination of Volmer step and parallel Tafel and Heyrovsky steps. At high negative potentials where the hydrogen coverage reaches its limiting value, a Tafel line with the slope of -... 

Series of quaternary ammonium salts of substituted five-membered-ring iron complexes were prepared by reaction of allyl(cyclopentadienyl)iron(II) dicarbonyl with iminium salts. Also, reactions of allyl-(cyclopentadienyl) iron(II) dicarbonyl with in situ prepared iminium salts afford the same products in good to excellent isolated yields. © 2007 American Chemical Society  

An operationally simple and entirely green protocol for heteropoly acid catalyst conjugate addition of indoles and pyrrole to unsaturated carbonyl compounds and nitro-alkene in water was investigated. It is important that the products arising from 1,2-addition were not observed under the reaction conditions. Pyrroles also readily underwent Michael addition at Α-positions under the same reaction conditions. Indole and many of its derivatives are present in many substances commonly found in nature. Micheal addition reactions are performed in organic solvents with the reactions in water are relatively scarce. The Michael addition between indole and methyl vinyl ketone in the presence of... 

The reaction kinetics and chemical equilibrium of the reversible catalytic hydrolysis reaction of a methyl acetate to acetic acid and methanol using a strongly acidic ion exchange resin catalyst named Amberlyst 15 were studied. To investigate the different behavior of Amberlyst 15 in the adsorption of reactants and product species, the equilibrium behavior of binary non-reactive liquid mixtures, consisting of one reactant and one product were studied experimentally. The Langmuir model was used to describe the equilibrium condition, quantitatively. Then the employed model was compared with the more complicated thermodynamic models to describe the equilibrium between the catalytic polymer... 

A simple, fast and efficient benign procedure has been developed for one-pot synthesis of 2-substituted benzothiazoles in the presence of zirconium(IV) oxide chloride octahydrate (ZrOCl2·8H 2O) and anhydrous copper(II) sulfate. The reaction of 2-aminothiophenol with aldehydes and anhydrides was carried out efficiently in solvent-free conditions with or without microwave irradiation, and adducts were produced in good to excellent yields. © 2006 Wiley Periodicals, Inc  

An efficient and simple method for the reduction of aldehydes, ketones and acid chlorides has been accomplished by using NaBH4-solid LiClO 4 in mild conditions at ambient temperature with complete chemoselectivity in reduction of α,β-unsaturated aldehydes and ketones. The reaction is fast with high yield and simple workup. Copyright © Taylor & Francis, Inc  

In recent years, polyethylene glycol (PEG) has attracted special attention as a green and inexpensive solvent in various chemical transformations. The current critical review deals with breakthrough achievements for the applications of PEG as an alternative reaction media well-known coupling reactions such as Suzuki, Heck, Stille, Sonogashira, Hiyama and some challenging organic reactions for carbon-carbon bond formation