Dielectric heating using microwave

Dabirmanesh, Q. and Roberts, R.M.G., The synthesis of iron sandwich complexes by microwave dielectric heating using a simple solid C02-cooled apparatus in an unmodified commercial microwave Oven, /. Organomet. Chem., 1993, 460, C28. 

There are two electromagnetic processes in use today induction and dielectric. Induction is more widely used, and there are several equipment manufacturers that will provide individual heaters or complete bonding systems. Dielectric heating, primarily microwave heating, is less utilized but is finding application in certain niche markets. 

The rubber industries use alkanolamines as secondary vulcanization accelerators to give improved mechanical properties and better heat resistance. Alkanolamines help stabilize rubber dispersions and may also act as an antioxidant for some rubbers. Alkanolamines are activators for the dielectric heating and microwave vulcanization processes. The various alkanolamines are used in the cold cure of certain rubbers and can act as chain termination agents in the chloroprene polymerization. 

Investigation of the microwave-assisted attachment of Fmoc-protected amino acids onto 2-chlorotrityl chloride resin indicated higher loadings and increased rates compared to standard room temperature procedures [146]. In this comparative study standard procedures yielded 0.37 mmol/g loading after 1 hour, whereas at 110 °C using microwave dielectric heating, a similar result (0.38 mmol/g) was obtained after only 15 min (Fig. 7). 

Increasing the interface by rapid stirring, use of ultrasound, microwave dielectric heating, etc. 

Larsson Brelid, P., Simonson, R. and Risman, P.O. (1999). Acetylation of wood using microwave heating. Part 1. studies of dielectric properties. Holz als Roh- und Werkstoff, 57(4), 259-263. 

Bazureau s group reported extensive work with TSILs for synthesis of various 4-thiazolidinones, 1,4-dihydropyridines, 3,4-dihydropyrimidin-2(lH)-ones and polyhydroquinones. They functionalized imidazole compounds with esters, which were then reacted with reagents to afford the target compound. They report that microwave dielectric heating is a useful aid to rapidly produce the desired product in high yields. 

Chemicals and the containment materials for chemical reaction do not interact equally with the commonly used microwave frequencies for dielectric heating and consequently selective heating may be achieved. Specifically, it is possible to cool the outside of the vessel with a coolant that is transparent to microwaves (solid C02 or liquid N2) and thereby have cold walls that still allowthe microwave energy to penetrate and heat the reactants, which are microwave active, in the vessel. Also for solid-state reactions contamination from the crucible walls may be minimised. 

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