Current Microwave Chemistry - Volume 3, Issue 1, 2016

A facile method of layered europium hydroxonitrate (LEuH) synthesis based on hydrothermal- microwave treatment of hexamethylenetetramine (HMT) and europium (III) nitrate mixed solutions is reported. Synthetic conditions, including microwave power, heating rate, temperature and duration of microwave treatment and filling coefficient of the hydrothermal reactor strongly affect the microstructure of LEuH. Obtained layered materials possess good anion-exchange properties. This work provides a simple and time-saving route to the europium layered hydroxides, which might represent a promising method for preparation of other layered rare-earth hydroxides.

This paper describes the bioreduction of four fluoroacetophenones with thermophilic bacteria (Bacillus sp. FPZSP005, B. subtilis FPZSP088, B. licheniformis FPZSP055 and BC-FPZSP051). The reduction reactions were performed under microwave irradiation and the thermophilic bacteria of the Bacillus genus provided moderate conversions to fluoroalcohols with yields in the 26-42% ranges and 5-62% e.e. When the reactions were carried out under conventional heating, they showed high conversions and selectivities (up to > 99% e.e.). This is the first study in the literature on the use of microwave irradiation with thermophilic bacteria applied on biocatalysis.

We describe here a simple and rapid protocol for the synthesis of (arylselanyl)phenyl-1H- 1,2,3-triazoles by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions using Microwave Irradiation. The products were obtained under mild conditions in excellent yields in a short reaction time by reacting azidophenyl arylselenides with a range of terminal alkynes using catalytic amount of Cu(OAc)2.H2O/sodium ascorbate. This Click Chemistry protocol is an efficient method to synthesize new selenium compounds with potential application in biological studies and materials sciences.

A convenient one-pot, multi-component and solvent free procedure for the preparation of substituted 2-amino-5-aryl-1,3,4-oxadiazoles has been achieved. The method is a significant improvement over previously reported synthesis. Reaction of acid chlorides with hydrazine hydrate and isothiocynates under microwave-irradiation (MWI) afforded the corresponding 1,3,4-oxadiazole derivatives in high yields with high purity. All synthesized compounds were characterized by FT-IR, proton and carbon NMR, mass spectroscopy and elemental analysis. A possible mechanism is proposed for the cyclodesulfurization based on the results of this study.

The objective of this study was to develop an efficient technique for enhancing the synthesis of sulfosuccinic acid diester sodium salt, required for industrial purposes. A series of gemini surfactants containing two symmetrical nonionic groups and an anionic moieties (polyoxyethylene stearyl ether sodium sulfosuccinate: PSSE-n) are synthesized via additive reaction of the double bond with sodium hydrogen sulfite under ultrasonic-microwave co-irradiation in solvent-free process. The structure of products is confirmed by FT-IR and 1H NMR. Sulfonation reaction conditions are discussed by single factor method. The optimal sulfonation reaction conditions are as follows: (i) n (maleic acid diester): n (sodium hydrogen sulfite) =1:1, (ii) microwave / ultrasonic power of 300 W / 360 W, (iii) reaction temperature 70°C, reaction time 60 min. Under the optimal conditions, series of products have reached up to a sulfonation rate of 75%-80%. The sulfonation reaction temperature drops by 22°C-25°C and the reaction time reduces for 35 hours comparing to the conventional approach.

Simulated wastewater containing methyl orange (MO C14H14N3NaO3S) was treated using a microwave (MW)-catalyzed reaction oxidative degradation (MCROD) method using MW catalyst TiO2/AC without H2O2, O2 or other oxidants. The effects of the MW power, irradiation time, catalyst loading and initial MO concentration were investigated regarding the degradation rate of MO. The degradation rate increased when increasing the MW power, irradiation time, and catalyst loading and decreased when increasing the initial MO concentration. For the simulated wastewater with an initial concentration of 100 mg/L MO, the degradation rate was 99.2% at a MW power of 600 W over 12 minutes with 22 g/L of TiO2/AC. This study explored the mechanism for the MCROD of MO: the formation of hydroxyl radicals (•OH) catalyzed by MW and the oxidative degradation of MO by the •OH in an aqueous solution. A detailed mechanism was also proposed. Studying the dynamics of the reaction revealed that the oxidation reaction was first-order.

An efficient and green protocol for the synthesis of β-aminocarbonyl and β-aminonitrile compounds has been developed. Near quantitative yield is achieved by mixing of a primary or a secondary amine with an α,β-unsaturated carbonyl compound under microwave irradiation in the presence of indium(III) triflate as the catalyst in glycerol as a green solvent. The reaction is simple, clean and complete within a few minutes and the product needs no purification.

The present manuscript deals with the effectiveness of mineral, LiNTf2 supported and ionic liquid, 3-methyl-1-octyl-imidazolium tetrachloroaluminate mediated Diels-Alder reactions of isoprene with maleic acid and 2-cyclohexene-1-one in conventional and microwave techniques. The Diels- Alder reactions of isoprene with maleic acid and 2-cyclohexene-1-one proceeded efficiently and smoothly in the presence of the minerals to provide the Diels-Alder adduct in moderate to excellent yields at various reaction conditions. A promising advantage of this green method is that the entire ionic liquid/LiNTf2 system can be recovered and reprocessed up to five runs without an appreciable loss of activity. The solid support LiNTf2 possesses commanding mechanical features that increased the catalytic efficiency in polar ionic liquid.

Some new trifluoromethyl coumarin thiosemicarbazones 3a-3m were synthesized by condensation reaction of thiosemicarbazides and 3-trifluoroacetyl coumarins which was from recyclization of ethyl 2-hydroxy-2-(trifluoromethyl)-2H-chromene-3-carboxylates under microwave assisted and solvent-free conditions. The structure of the synthesized compounds were characterized by IR, 1H NMR, 13C NMR, HRMS and X-ray, and their antifungal activity was evaluated. Most of them exhibited potent antifungal activity by comparison with the standard drugs.

The homogeneous microwave-assisted sulfuric acid-catalyzed transesterification of soybean oil, waste Brazil nut oil, sunflower oil and chicken fat for ethylic and methylic biodiesel production is described herein. The experiments were carried out in pilot-scale multimode reactors. The effects of the alcohol to oil molar ratio, catalyst concentration and irradiation time on the conversion to biodiesel were investigated. The transesterification reactions were performed at relatively small alcohol to oil molar ratios (9:1, 8:1 and 6:1) affording near 100% of conversion in reaction times of 60 to 120 min. Partial least squares (PLS) regression analysis using FT-NIR spectroscopy was performed to monitor the progress of the acid-catalyzed methanolysis of soybean oil. The NIR spectra were collected during the transesterification reaction with a spectrophotometric continuous-flow cell. 1H NMR spectroscopy was employed to determine the conversion percentage and used as a reference to build the PLS calibration model employing NIR spectroscopy data.

A series of compounds having the pyranopyrazole pharmacophore were synthesised by the traditional method and then by an unreported rapid four-component microwave assisted method. The microwave strategy required substantially shorter reaction times as compared to the traditional method. The prepared molecules were tested in-vitro for their cytotoxic activity against the Hep3B cancer cell lines. The activity results were subsequently rationalized for a quick structure-activity relationship leading to the conclusion that the presence of certain heteroatom substituents at a 3-position of the pharmacophore may be crucial for anticancer potency.

The synthesis of Ni-containing layered silicate clays from the lizardite-nepouite series (1:1) and kerolite-pimelite series (2:1) with random distribution of octahedral cations was feasible with the microwave-assisted hydrothermal synthesis method. These series were obtained from co-precipitate gels with Si2Mg3-xNixO7.nH2O and Si4Mg3-xNixO11.nH2O (x = 0, 0.5, 1, 1.5, 2, 2.5, and 3) compositions. Syntheses were performed at 220°C during 48 hours under equilibrium water pressure using microwave furnace. X-ray diffraction revealed pure 1:1 and 2:1 synthesized phyllosilicates for the lizardite and the kerolite series, respectively. Fourier transform infrared spectroscopy in both near and mid infrared regions revealed a random distribution of Ni cations in the octahedral sheet of 1:1 and 2:1 silicate clays, that is a good requirement for material applications, especially for the synthesis of metallic catalysts.