Etherification of benzyl alcohol under microwave irradiation using a heteropoly acid as catalyst

Selective dehydration of benzyl alcohol to dibenzyl ether using heteropoly acid as catalyst in solvent-free conditions under microwave irradiation has been studied. The microwave power and irradiation time, and concentration of heteropoly acid are key factors, and under the severe conditions dibenzyl ether was polymerized. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nanofiber cellulose di- and tri-acetate using ferric chloride as a catalyst promoting highly efficient synthesis under microwave irradiation

An efficient method for the generation of cellulose di- and tri-acetate nano-structures is obtained through testing ferric chloride hydrate (FeCl₃·6H₂O) as a valuable Lewis acid catalyst with acetic anhydride under microwave irradiation. Our target was to evaluate the effects of the reaction conditions on the products' properties such as surface area and particle size distribution. It was found that changes in the degree of substitution (DS), the surface area, the degree of polymerization and the particle size distribution of the products correlated with reaction conditions. Cellulose tri-acetate nanofibers with DS of 2.94 with 98.03% yield was prepared using 200 mg of FeCl₃·6H₂O, 25 ml of Ac₂O and 4 minutes of microwave irradiation. Also, cellulose di-acetate nanofibers were prepared with DS values ranged between 2.37 and 2.72 with yield ranged between 78.92 and 90.58%. The percentage of acetyl groups (Ac%) as well as the BET specific surface area, total pore volume, mean pore diameter, mono layer volume and the mean particle size of the products were determined. The maximum specific surface area obtained for the acetylated cellulose was about ten times larger than that measured for the commercial cotton cellulose and about six times larger than that of the commercial cellulose acetate. The lowest mean particle size (34.90 nm) was about eleven times smaller than the mean particle size of the commercial cellulose acetate (394 nm). The present work has proved that FeCl₃·6H₂O was a highly active catalyst for the esterification of cellulose with unexpected yields and for the formation of nanofibers with low molecular weight.     

Silica sulfate as a recyclable and efficient catalyst for Beckmann rearrangement under microwave irradiation

Silica sulfate has been proved to be an efficient and recyclable catalyst for Beckmann rearrangement of a variety of oximes in acetone under microwave irradiation. This protocol has advantages of high conversion, high selectivity, short reaction time, no environmental pollution, and simple work-up procedure.     

I_2/离子液体作为可回收均相催化剂在微波条件下高效制备全乙酰糖(英文)

以可回收的I2/PEG400型离子液体(I2/IL400)为催化体系,发展了一种高效、实用的合成全乙酰糖衍生物的方法.结果表明,以糖与乙酸酐为原料,在微波辐射、无溶剂条件以及I2/IL400体系中,数分钟之内可以非常高的产率(90%–99%)和数十毫摩尔规模(50.0 mmol)制备出全乙酰糖.通过简单的甲苯萃取,可以从I2/IL400体系中分离出全乙酰糖,I2/IL400体系可循环使用6次,且产率均在90%以上.当反应规模扩大到50.0 mmol时,该体系依然能高效快速地催化糖的全乙酰化,并且可以循环使用5次,产率依然维持在90%左右.     

Clean one-pot synthesis of 1,2,4-oxadiazoles under solvent-free conditions using microwave irradiation and potassium fluoride as catalyst and solid support

Potassium fluoride was found to be an efficient catalyst and solid support for the synthesis of 3,5-disubstituted-1,2,4-oxadiazoles. In this work, a one-pot method for the synthesis of these compounds from the reaction of nitriles with hydroxylamine hydrochloride and acyl chloride in the presence of potassium fluoride under solvent-free conditions using microwave irradiation has been developed. The advantages of using potassium fluoride as a solid support in comparison to conventional solid supports are simple operation and convenient separation of the products.     

Solvent-free,scalable and expeditious synthesis of benzanilides under microwave irradiation using clay doped with palladium nanoparticles as a recyclable and efficient catalyst

Benzanilide synthesis through amide bond formation was effectively carried out by palladium-doped clay catalyst using microwave irradiation under solvent-free conditions. Products were obtained with excellent yield in very short reaction time and only a small amount of the catalyst was used. The catalyst could be separated easily and recycled several times with insignificant loss in catalytic activity. No column purification was required and the products were purified by the crystallization method. The heterogeneous character of the catalyst in a ligand-free, solvent-free and base-free system supports for a practical and environmentally benign process.     

Green synthesis of 3,4-dihydropyrimidinones using nano Fe3O4@meglumine sulfonic acid as a new efficient solid acid catalyst under microwave irradiation

Design, synthesis and characterization of nano Fe₃O₄@meglumine sulfonic acid as a new solid acid catalyst for the simple and green one pot multicomponent synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones was studied. New solid acid catalyst was prepared through a clean and simple protocol and characterized using FTIR, VSM, TGA, SEM, elemental analysis (CHN) and XRD techniques. Heterogenization of homogeneous catalyst as a green approach is a useful method for enhancing the efficiency of catalyst. Presented study was a new method for attachment of homogeneous highly soluble catalyst (meglumine sulfate) to the magnetite nanoparticle surfaces for preparing a heterogeneous and effective catalyst. Obtained heterogeneous and reusable solid acid catalyst has high performance in the synthesis of Biginelli compounds. The reaction was performed under microwave irradiation as a rapid and green condition. Easy work up as well as excellent yield (90–98%) of products in short reaction times (40–200 s) and reusable catalyst are the main advantages of presented procedure. Reaction products were characterized in details using physical and chemical techniques such as melting point, ¹H NMR, ¹³C NMR and FTIR.     

Cellulose sulfuric acid as a bio-supported and recyclable solid acid catalyst for the one-pot synthesis of 2,4,5-triarylimidazoles under microwave irradiation

Abstract

A simple, rapid, and highly efficient method has been attempted for the three-component condensation of benzil/benzoin, aldehydes, and ammonium acetate under microwave irradiation in the presence of a catalytic amount of bio-supported cellulose sulfuric acid under solvent-free conditions to afford the 2,4,5-triarylimidazole derivatives. The catalyst is easily prepared, inexpensive, separated simply by filtration, gives excellent yield of products with shorter reaction times, and is recyclable several times.     

Deprotection of oximes using urea nitrate under microwave irradiation

A new mild and efficient method for the cleavage of oximes to carbonyl compounds using readily available urea nitrate in acetonitrile-water (95:5), under microwave irradiation within 2 min, in good yields is reported     

Facile and green synthesis of triarylmethanes using silica sulfuric acid as a reusable catalyst under solvent-free conditions

A facile and environmentally-benign protocol has been developed for the synthesis of triarylmethanes (TAMs) from the reaction of different arenes and aldehydes in the presence of silica sulfuric acid (SSA) as a heterogeneous and reusable catalyst under solvent-free conditions. Easy work-up, short reaction times, high yields, high selectivity, mild and green conditions are other salient features of this method.     

One-Pot Synthesis of 1-Aminophosphinic acids using 50% Hypophosphorus Acid under microwave irradiation

A simple and efficient method has been developed for the synthesis of α-aminophosphinic acids from hypophosphorus acid under solvent-free conditions using microwave irradiation. α-Aminophosphinic acids were obtained in high yield under mild conditions by reaction of hypophosphorus acid with aldehydes in the presence of amines under microwave irradiation.     

Preparation of phenytoin derivatives under solvent-free conditions using microwave irradiation

Russian Journal of Organic Chemistry -     

Facile construction of symmetric biaryls using (BeDABCO)2Pd2Cl6 as an efficient and highly active catalyst under microwave irradiation

An efficient catalytic system using (BeDABCO)₂Pd₂Cl₆ (BeDABCO, benzyl‐1,4‐diazabicyclo[2.2.2]octane) was developed for the homo‐coupling reaction of various aryl halides. Due to the combination of ionic homogeneous metal catalyst and microwave irradiation, symmetric biaryls were produced in excellent yields and short reaction times in N‐methyl‐2‐pyrrolidone at 120 °C. BeDABCO as an efficient ligand and also a quaternary ammonium salt had an efficient stabilizing effect on the Pd(0) species in this coupling reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrogen transfer type oxidation of alcohols by rhodium and ruthenium catalyst under microwave irradiation

Secondary alcohols were converted into the corresponding ketones by methyl acrylate and rhodium catalyst efficiently under microwave irradiation. Treatment of primary alcohols with the same condition resulted in the recovery of the starting materials. Primary alcohols were converted into aldehydes by hydrogen transfer reaction using methyl vinyl ketone and ruthenium catalyst under microwave irradiation.     

Hydrolysis of chitosan under microwave irradiation in ionic liquids promoted by sulfonic acid-functionalized ionic liquids

Hydrolysis of chitosan in ionic liquids was carried out under microwave irradiation (MW) using sulfonic acid-functionalized ionic liquids (SFILs) as catalysts. The effect of microwave power, irradiation time, dosage of SFILs and DMSO was investigated by orthogonal tests. Under the optimal reaction conditions, the yield of total reducing sugars (TRS) reached over 90% within 2 min. The viscosity-average molecular weight of degraded chitosan was determined by viscosity method. The structures of the original and degraded chitosan were characterized by Fourier-transform infrared (FTIR) spectra, X-ray powder diffraction (XRD) analysis and carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR). The influence of microwave power and irradiation time on the TRS and M_v was further studied. This method can dramatically reduce reaction time.     

Kinetics modeling of the volatilization of mercury compounds involved in spent mercury-containing catalyst under microwave irradiation

The industrial design and development of microwave-induced volatilization of hazardous substances in waste greatly depend on their dielectric properties. The dielectric properties of different mercury compounds in spent mercury-containing catalyst (SAC) were investigated by the cavity perturbation method at different temperatures. The decomposition absorption mechanisms for HgS and HgCl₂ show the same trend according to thermogravimetric analysis results over the temperature range of interest. The SAC composite exhibits sufficient microwave absorption from 20 °C to approximately 600 °C owing to the superior dielectric properties of non-volatile mercury-containing compounds (HgCl₂ and HgS). At temperatures above 600 °C, the dielectric properties of the SAC are determined by the residual mercury and carbon matrix. Phase analyses indicate that the entire process of microwave heating could be divided into three stages: (1) The volatilization temperature of unbound water and some impurities are between 20 °C and 100 °C; (2) The main thermal disintegration region of mercury species is between 100 °C and 600 °C; (3) HgCl₂ and HgS volatilize completely to gas at 600 °C. Meanwhile, HgCl₂ decomposing more readily than HgS.     

Rapid and efficient synthesis of 1-arylpiperazines under microwave irradiation

1-Arylpiperazines, finding wide applicability in pharmaceuticals were synthesized easily under microwave irradiation from bis(2-chloroethyl)amine hydrochloride and substituted anilines without any solvent. The reaction time was just 1–3 mins. 1-Arylpiperazines were synthesized in 53 to 73% yields. Potent serotonin ligands like Trifluoromethylphenylpiperazine (TFMPP) and 3-Chlorophenylpiperazine (mCPP) were also prepared in just 1 min. and 2 mins. respectively.     

The synthesis of unsubstituted cyclic imides using hydroxylamine under microwave irradiation

Unsubstituted cyclic imides were synthesized from a series of cyclic anhydrides, hydroxylamine hydrochloride (NH2OH.HCl), and 4-N,N-dimethylamino-pyridine (DMAP, base catalyst) under microwave irradiation in monomode and multimode microwaves. This novel microwave synthesis produced high yields of the unsubstituted cyclic imides for both the monomode (61 - 81%) and multimode (84 - 97%) microwaves.     

Iodination of alcohols using triphenylphosphine/iodine under solvent-free conditions using microwave irradiation

A straightforward and effective procedure for the conversion of benzylic, allylic and aliphatic alcohols to the corresponding iodides using Ph₃P/I₂ under solvent-free conditions using microwave irradiation is reported.