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J Org Chem. 2008 Aug 15;73(16):6321-9. doi: 10.1021/jo8009402. Epub 2008 Jul 10.

Investigating the existence of nonthermal/specific microwave effects using silicon carbide heating elements as power modulators.

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  • 1Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28, A-8010 Graz, Austria.


The use of passive heating elements made out of chemically inert sintered silicon carbide (SiC) allows microwave transparent or poorly absorbing reaction mixtures to be heated under microwave conditions. The cylindrical heating inserts efficiently absorb microwave energy and subsequently transfer the generated thermal energy via conduction phenomena to the reaction mixture. In the case of low to medium microwave absorbing reaction mixtures, the addition of SiC heating elements results in significant reductions (30-70%) in the required microwave power as compared to experiments performed without heating element at the same temperature. The method has been used to probe the influence of microwave power (electromagnetic field strength) on chemical reactions. Six diverse types of chemical transformations were performed in the presence or absence of a SiC heating element at the same reaction temperature but at different microwave power levels. In all six cases, the measured conversions/yields were similar regardless of whether a heating element was used or not. The applied microwave power had no influence on the reaction rate, and only the attained temperature governed the outcome of a specific chemical process under microwave conditions.

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