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Microwave Effects (microwave + effects)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

Microwave Effects in Solvent-Free Esters Aminolysis.

CHEMINFORM, Issue 27 2003
Laurence Perreux
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Green chemistry procedure for the synthesis of cyclic ketals from 2-adamantanone as potential cosmetic odourants

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2002
M. 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]

Microwave-Assisted Polymer Synthesis: State-of-the-Art and Future Perspectives

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2004
Frank Wiesbrock
Abstract Summary: Monomodal microwaves have overcome the safety uncertainties associated with the precedent domestic microwave ovens. After fast acceptance in inorganic and organic syntheses, polymer chemists have also recently discovered this new kind of microwave reactor. An almost exponential increase of the number of publications in this field reflects the steadily growing interest in the use of microwave irradiation for polymerizations. This review introduces the microwave systems and their applications in polymer syntheses, covering step-growth and ring-opening, as well as radical polymerization processes, in order to summarize the hitherto realized polymerizations. Special attention is paid to the differences between microwave-assisted and conventional heating as well as the "microwave effects". Results of search on number of publications on microwave-assisted polymerizations, sorted by year. [source]

Studies on microwaves in medicine and biology: From snails to humans

BIOELECTROMAGNETICS, Issue 3 2004
James C. Lin
Abstract This d'Arsonval Medal acceptance presentation highlights several research themes selected from Dr. Lin's published works, focusing on the microwave portion of the nonionizing electromagnetic spectrum. The topics discussed include investigation of microwave effects on the spontaneous action potentials and membrane resistance of isolated snail neurons, effects on the permeability of blood brain barriers in rats, the phenomenon and interaction mechanism for the microwave auditory effect (the hearing of microwave pulses by animals and humans), the development of miniature catheter antennas for microwave interstitial hyperthermia treatment of cancer, the application of transcatheter microwave ablation for treatment of cardiac arrhythmias, and the use of noninvasive wireless technology for sensing of human vital signs and blood pressure pulse waves. The paper concludes with some observations on research and other endeavors in the interdisciplinary field of bioelectromagnetics. Bioelectromagnetics 25:146,159, 2004. © 2004 Wiley-Liss, Inc. [source]

Microwave-Assisted Cross-Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition-Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

CHEMISTRY - A EUROPEAN JOURNAL, Issue 43 2009
Muhammed Irfan
Abstract The concept of specific microwave effects in solid/liquid catalytic processes resulting from the selective heating of a microwave-absorbing heterogeneous transition-metal catalyst by using 2.45,GHz microwave irradiation was evaluated. As model transformations Ni/C-, Cu/C-, Pd/C-, and Pd/Al2O3 -catalyzed carbon,carbon/carbon,heteroatom cross-couplings and hydrogenation reactions were investigated. To probe the existence of specific microwave effects by means of selective catalyst heating in these transformations, control experiments comparing microwave dielectric heating and conventional thermal heating at the same reaction temperature were performed. Although the supported metal catalysts were experimentally found to be strongly microwave absorbing, for all chemistry examples investigated herein no differences in reaction rate or selectivity between microwave and conventional heating experiments under carefully controlled conditions were observed. This was true also for reactions that use low-absorbing or microwave transparent solvents, and was independent of the microwave absorbtivity of the catalyst support material. In the case of hydrogenation reactions, the stirring speed was found to be a critical factor on the mass transfer between gas and liquid phase, influencing the rate of the hydrogenation in both microwave and conventionally heated experiments. [source]