Microwave heating effect

Table 4.3 Microwave heating effects of doping organic solvents with ionic liquids (IL) A and B (data from [63]). a ...

Microwave heating effects result primarily from the interaction of the electric component of the microwave with dipoles or charged particles in a material. The response of the system to such fluctuating fields is described by the complex dielectric constant, . 17 This may be expressed as the sum of real (ef) and imaginary (eff) dielectric constants ... 

Yoshida, H., Hirooka, N., and Kajimoto, G. 1991. Microwave Heating Effects on Relative Stabilites of Tocopherols in Oils. J. Food Sci. 56 1042-1046. 

According to the author, before claiming microwave heating effects in preference to collisional or mechanistic terms, it is necessary to estimate the effect of strong heating rates induced by microwave heating. The energy density used in a domestic oven is sufficient to raise temperature from ambient to 200 °C in less than 1 min, and so cause the total reaction time to be reduced by a factor dose to 10. ... 

Tab. 5.1. The microwave heating effects of adding a small quantity of ionic liquids, 8 and 9, to hexane, toluene, THF, and...

Robinson J, Kingman S, Irvine D et al (2010) Understanding microwave heating effects in single mode type cavities-theory and experiment. Phys Chem Chem Phys 12 4750-4758... 

Terminal chelation controlled Heck vinylations of electron-rich amino-functionalized vinyl ethers were performed with high regioselectivity to furnish the corresponding 1-alkoxy-l,3-butadienes. Controlled microwave heating effectively accelerated these palladium catalyzed reactions and full conversion could be achieved... 

Microwave Cooking Pads. A simple and effective method of reducing fat in meat products involves the use of microwavable heating pads. 

Most, if not all, microwave biological effects and potential medical appHcations are beheved to be the result of heating, ie, thermal effects. The phenomenon of microwave hearing, ie, the hearing of clicking sounds when exposed to an intense radar-like pulse, is generally beheved to be a thermoelastic effect (161). Excellent reviews of the field of microwave bioeffects are available (162,163). 

Reports of sterilisation (qv) against bacteria by nonthermal effects have appeared, but it is generally beheved that the effect is only that of heating (164). Because microwave heating often is not uniform, studies in this area can be seriously flawed by simplistic assumptions of uniform sample temperature. 

Bu3Sn)20 BzCl. The use of microwaves accelerates this reaction. Bu2Sn(OMe)2 is reported to work better than Bu2SnO in the monoprotection of diols. The monoprotection of diols at the more hindered position can be accomplished through the stannylene if the reaction is quenched with PhMe2SiCl (45-77% yield).Microwave heating has been found to be effective for this transformation in some cases. ... 

During the past decade, MALDI-TOF MS has proven to be an effective tool for the analysis of oligo- and polymeric mannoglucans (for extensive reviews see [222,223]). SEC/MALDI mass spectrometry was employed in the analysis of hemicelluloses isolated by microwave heat-fractionation from spruce and aspen wood [94]. These methods allowed the separation and characterization of the oligo- and polysaccharide fractions derived from the xylan and mannan components of both woods [224]. 

Finally, dissolution of non-activated cellulose in LiCl/DMAc, and in ionic liquids has been accelerated by microwave irradiation [72,103,104], although the effect of microwave heating on the DP of the polymer has not been investigated. This last point is relevant in view of the fact that ILs are heated with exceptional efficiency by microwaves [105], so that care must be taken to avoid excessive localized heating that can induce chain degradation of the polymer during its dissolution. 

Fig. 1 Effect of temperature on NH3 oxidation. Closed symbols electric finnace, open symbols microwave heating,, O NH3 conversion, A, A N2 selectivity,, NO selectivity, BO N2O selectivity.

Freitag and John [96] studied rapid separation of stabilisers from plastics. Fairly quantitative extraction (>90% of the expected content) of stabilisers from a powdered polymer was achieved by MAE within 3 to 6 min, as compared to 16 h of Soxhlet extraction for the same recovery. MAE and Soxhlet extraction have also been compared in the analysis of cyclic trimer in PET [113]. On the other hand, Ganzler et al. [128] compared the extraction yields for various types of compounds from nonpolymeric matrices for microwave irradiation with those obtained by the traditional Soxhlet or shake-flask extraction methods. Microwave extraction was more effective than the conventional methods, in particular in the case of polar compounds. As expected, the efficiency of the former is high especially when the extraction solvents contain water. With the high dipole moment of water, microwave heating is more... 

In conclusion, metal nanoclusters in DMF interact strongly with microwaves. In reactions catalysed by these clusters, the microwave heating may be tantamount to preferentially heating the catalytic site, which can lead to more effective catalysis. Such cluster-catalysed reactions can be in principle screened in parallel in multimode m/w ovens reducing both time and operational costs. However, the ovens must be adapted so that the parallel reactors are uniformly heated. 

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