Home About us Contact
|
Home About us Contact | ||
|
|
||
Microwave Activation (microwave + activation)
Selected AbstractsMicrowave Activation of Electrochemical Processes at Glassy Carbon and Boron-Doped Diamond ElectrodesELECTROANALYSIS, Issue 5-6 2005Kumar Sur, Ujjal Abstract Voltammetric experiments under intense microwave field conditions have been carried out at a carbon microfiber electrode, an array of carbon microfiber electrodes, and at a boron-doped diamond electrode. For the reversible one electron redox systems Fe(CN) and Ru(NH3) in aqueous KCl solution increased currents (up to 16 fold at a 33,,m diameter carbon microelectrode) and superheating (up to ca. 400,K at all types of electrodes) are observed. Electrodes with smaller diameter allow better signal enhancements to be achieved. From the missing effect of the supporting electrolyte concentration on the microwave enhanced currents, it can be concluded that effects observed at carbon electrodes (microwave absorbers) are due to the interaction of microwaves with the electrode material whereas for metal electrodes (microwave conductors) effects are dominated by the interaction of the microwaves with the aqueous dielectric. Short heat pulses can be applied by pulsing the microwave field and relatively fast temperature transients are observed for small electrodes. For the irreversible two electron oxidation of L -dopa in aqueous phosphate buffer, different types of effects are observed at glassy carbon and at boron-doped diamond. Arrays of carbon microfibers give the most reproducible and analytically useful current signal enhancements in the presence of microwaves. [source] ChemInform Abstract: An Unusual, Mild and Convenient One-Pot Two-Step Access to (E)-Stilbenes from Hydroxy-Substituted Benzaldehydes and Phenylacetic Acids under Microwave Activation: A New Facet of the Classical Perkin Reaction.CHEMINFORM, Issue 6 2008Arun K. Sinha Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] One-Pot Dry Media Synthesis of New Tetracyclic 1,5-Benzothiazepines under Microwave Activation.CHEMINFORM, Issue 27 2003Anshu Dandia Abstract For Abstract see ChemInform Abstract in Full Text. [source] A Rapid One-Pot Synthesis of 2,4,6-Triaryl-3-aroyl-4-hydroxy-1,1-cyclohexanedicarbonitriles and 2-Aminoisophthalonitriles under Microwave Activation.CHEMINFORM, Issue 16 2003Dhrubojyoti D. Laskar Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Solvent-Free Synthesis of Tartramides under Microwave Activation.CHEMINFORM, Issue 14 2002F. Massicot Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Modeling of Polymerization Kinetics and Molecular Weight Development in the Microwave-Activated Nitroxide-Mediated Radical Polymerization of StyreneMACROMOLECULAR REACTION ENGINEERING, Issue 2-3 2009Jorge J. Hernández-Meza Abstract Calculations of the polymerization rate and molecular weight development in the nitroxide-mediated radical polymerization (NMRP) of styrene (STY), using hydroxyl-TEMPO and dibenzoyl peroxide (BPO), and activated by microwave irradiation (MI), are presented. The calculations are based on a kinetic model developed in our group. Microwave activation is modeled by three approaches: microwave-activated production of free radicals from monomer molecules, microwave-enhanced thermal initiation, and microwave-enhanced dormant polymer activation. The results obtained are compared against experimental data from the literature. The first approach is the most adequate. The NMRP of STY using TEMPO, BPO, and conductive heating, and the NMRP of STY activated by MI, without initiator, are also analyzed as reference cases. [source] A Microwave-Assisted Heck Reaction in Poly(ethylene glycol) for the Synthesis of BenzazepinesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2007Valérie Declerck Abstract The Heck reaction of alkylated 2-(trimethylsilyl)ethanesulfonyl (SES)-protected ,-amino esters provides benzazepines in good yields. Good selectivity towards cyclisation was obtained when the reaction was performed in PEG 3400 as the solvent under microwave activation. Cleavage of the SES group with HF provides the corresponding free benzazepine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Green chemistry procedure for the synthesis of cyclic ketals from 2-adamantanone as potential cosmetic odourantsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2002M. T. Genta Synopsis Some cyclic ketals derived from 2-adamantanone were obtained in excellent yields by microwave activation under solvent-free conditions, as a ,green chemistry' procedure. A number of experiments were performed to evaluate the most efficient catalytic conditions. The best results were obtained using a simple heterogeneous mixture of reagents and p -toluenesulphonic acid as the catalyst, without any solvent or support. The data are reported and compared with those obtained by other microwave-mediated syntheses or by classical method. In order to check the possible intervention of non-thermal microwave effects, the best experiment in ,dry media' was carried out with considerable lower yield by conventional heating, in a thermostated oil bath, under the same conditions as under microwaves (time, temperature and vessel). All the synthesized compounds were tested for their olfactive character and for a potential cosmetic use. The odour evaluation is reported. Résumé Des acétals cycliques dérivés de la 2-adamantanone ont été obtenus sous irradiation microonde sans solvant avec d'excellents rendements selon un procédé de ,chimie verte'. Un certain nombre d'experiences ont été réalisées pour optimiser les conditions de réaction. Les résultats obtenus par simple mélange hétérogène des réactifs et de l'acide p -toluènesulphonique 10% (p/p) comme catalyseur ont été décrits et comparés avec ceux obtenus avec les autres procédés, sous irradiation microonde ou par chauffage traditionnel. Dans le but de mettre en évidence l'éventuelle intervention d'effets spécifiques (non-purement thermiques) des microondes, la meilleure réaction obtenue en ,milieu sec' a été effectuée, avec des rendements nettement plus faibles, dans les mêmes conditions (temps et température), par chauffage classique. Les propriétés olfactives de tous les produits obtenus ont été déterminées pour évaluer une possible utilization cosmétique. [source] Green chemistry for the second generation biorefinery,sustainable chemical manufacturing based on biomassJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2007James H Clark The material needs of society are reaching a crisis point. The demands of a growing and developing world population will soon exceed the capacity of our present fossil resource based infrastructure. In particular, the chemical industry that underpins most industries needs to respond to these challenges. The chemical manufacturing and user industries face an unprecedented range and intensity of drivers for change, the greatest of which, REACH (Registration, Evaluation and Authorisation of Chemicals) has yet to bite. In order to address the key issues of switching to renewable resources, avoiding hazardous and polluting processes, and manufacturing and using safe and environmentally compatible products, we need to develop sustainable and green chemical product supply chains. For organic chemicals and materials these need to operate under agreed and strict criteria and need to start with widely available, totally renewable and low cost carbon,the only source is biomass and the conversion of biomass into useful products will be carried out in biorefineries. Where these operate at present, their product range is largely limited to simple materials (e.g. cellulose), chemicals (e.g. ethanol) and bioenergy/biofuels. Second generation biorefineries need to build on the need for sustainable chemical products through modern and proven green chemical technologies such as bioprocessing, controlled pyrolysis, catalysis in water and microwave activation, in order to make more complex molecules and materials on which a future sustainable society will be based. Copyright © 2007 Society of Chemical Industry [source] Radiosynthesis of 2- exo -(2,-[18F]Fluoro-3,-(4-fluorophenyl)-pyridin-5,-yl)-7-azabicyclo[2.2.1]heptane ([18F]F2PhEP), a potent epibatidine-based radioligand for nicotinic acetylcholine receptor PET imagingJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 6 2006Gaëlle Roger Abstract 2- exo -(2,-Fluoro-3,-(4-fluorophenyl)-pyridin-5,-yl)-7-azabicyclo[2.2.1]heptane (F2PhEP), a novel, epibatidine-based, ,4,2-selective nicotinic acetylcholine receptor antagonist of low toxicity, as well as the corresponding N- Boc-protected chloro- and bromo derivatives as precursors for labelling with fluorine-18 were synthesized from 7- tert -butoxycarbonyl-7-azabicyclo[2.2.1]hept-2-ene in 13, 19 and 8% overall yield, respectively. [18F]F2PhEP was prepared in 8,9% overall yield (non-decay-corrected) using 1 mg of the bromo derivative in the following two-step radiochemical process: (1) no-carrier-added nucleophilic heteroaromatic ortho- radiofluorination with the activated K[18F]F-Kryptofix®222 complex in DMSO using microwave activation at 250 W for 90 s, followed by (2) quantitative TFA-induced removal of the N -Boc protective group. Radiochemically pure (>95%) [18F]F2PhEP (1.48,1.66 GBq, 74,148 GBq/µmol) was obtained after semi-preparative HPLC (Symmetry® C18, eluent aqueous 0.05 M NaH2PO4 CH3CN: 78/22 (v:v)) in 75,80 min starting from an 18.5 GBq aliquot of a cyclotron-produced [18F]fluoride production batch. Copyright © 2006 John Wiley & Sons, Ltd. [source] Synthesis of 4-[18F]fluoroiodobenzene and its application in sonogashira cross-coupling reactionsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 8 2003Frank R. Wüst Abstract The first application of a Sonogashira cross-coupling reaction in 18F chemistry has been developed. The reaction was exemplified by the cross-coupling of terminal alkynes (ethynylcyclopentyl carbinol 6, 17,-ethynyl-3,17,-estradiol 7 and 17,-ethynyl-3-methoxy-3,17,-estradiol 8) with 4-[18F]fluoroiodobenzene. 4,4,-Diiododiaryliodonium salts were used as precursors for the synthesis of 4-[18F]fluoroiodobenzene, enabling the convenient access to 4-[18F]fluoroiodobenzene in 13,70% yield using conventional heating or microwave activation. The Sonogashira cross-coupling of 4-[18F]fluoroiodobenzene with terminal alkynes gave the corresponding 4-[18F]fluorophenylethynyl-substituted compounds [18F]-9, [18F]-10 and [18F]-13 in yields up to 88% within 20 min of starting from 4-[18F]fluoroiodobenzene. Copyright © 2003 John Wiley & Sons, Ltd. [source] Ortho -[18F]Fluoronitrobenzenes by no-carrier-added nucleophilic aromatic substitution with K[18F]F,K222,A comparative studyJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2002M. Karramkam Abstract The scope of the nucleophilic aromatic ortho -fluorinations from the corresponding ortho -halonitrobenzene precursors (halo-to-fluoro substitutions) with no-carrier-added [18F]fluoride ion as its activated K[18F]F,K222 complex has been evaluated via the radiosynthesis of ortho -[18F]fluoronitrobenzene, chosen as a model reaction. The parameters studied include the influence of the leaving group in the ortho position of the phenyl ring (,Cl, ,Br, ,l), the quantity of precursor used, the type of activation (conventional heating or microwave irradiations), the solvent, the temperature and the reaction time. The iodo-precursor was completely unreactive and the bromo-precursor gave only low incorporation (<10%) in the optimal conditions used (conventional heating at 145°C or microwave activation, 100 W for 120 s). Only the chloro-precursor was found reactive in the conditions described above and up to 70% yield was observed for the formation of ortho -[18F]fluoronitrobenzene ([18F]- 1). In all the experiments, the unwanted ortho -[18F]fluoro-halobenzenes, potentially resulting from the nitro-to-fluoro substitution, could not be detected. These results will be applied for the radiosynthesis of 5-[18F]fluoro-6-nitroquipazine, a potent radioligand for the imaging of the serotonin transporter with PET. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||