DOI: 10.1002/chem.201001703 Sintered Silicon Carbide: A New Ceramic Vessel Material for Microwave Chemistry in Single-Mode Reactors Bernhard Gutmann, David Obermayer, Benedikt Reichart, Bojana Prekodravac, Muhammad Irfan, Jennifer M. Kremsner, and C. Oliver Kappe* [a] Introduction Microwave chemistry generally relies on the ability of the reaction mixture to efficiently absorb microwave energy, taking advantage of microwave dielectric heating phenom- ena such as dipolar polarization or ionic conduction mecha- nisms. [1] This produces efficient and rapid internal heating (in-core volumetric heating) by direct interaction of electro- magnetic irradiation with the molecules (solvents, reagents, catalysts) that are present in the reaction mixture. [1] For mi- crowave irradiation to be able to penetrate to the reaction mixture, reaction vessels employed in microwave chemistry are typically made out of low microwave absorbing or mi- crowave transparent materials, such as borosilicate glass (Pyrex), quartz, or suitable polymers like PTFE (Teflon). [2] These materials exhibit many distinct and valuable advan- tages when used in microwave chemistry, but also face some limitations in high-end applications under extreme reaction conditions as far as temperature/pressure resistance, or chemical stability to aggressive media is concerned. Prob- lems also exist when attempting to heat microwave transpar- ent or low-absorbing reaction media in these types of reac- tion vessels. In recent years, the use of sintered silicon carbide (SiC) has become increasingly popular for a variety of applica- tions in microwave chemistry. SiC is a strongly microwave absorbing chemically inert ceramic material that can be uti- lized at extremely high temperatures due to its high melting point (  2700 8C) and very low thermal expansion coeffi- Abstract: Silicon carbide (SiC) is a strongly microwave absorbing chemi- cally inert ceramic material that can be utilized at extremely high temperatures due to its high melting point and very low thermal expansion coefficient. Mi- crowave irradiation induces a flow of electrons in the semiconducting ceram- ic that heats the material very efficient- ly through resistance heating mecha- nisms. The use of SiC carbide reaction vessels in combination with a single- mode microwave reactor provides an almost complete shielding of the con- tents inside from the electromagnetic field. Therefore, such experiments do not involve electromagnetic field ef- fects on the chemistry, since the semi- conducting ceramic vial effectively pre- vents microwave irradiation from pene- trating the reaction mixture. The in- volvement of electromagnetic field ef- fects (specific/nonthermal microwave effects) on 21 selected chemical trans- formations was evaluated by compar- ing the results obtained in microwave- transparent Pyrex vials with experi- ments performed in SiC vials at the same reaction temperature. For most of the 21 reactions, the outcome in terms of conversion/purity/product yields using the two different vial types was virtually identical, indicating that the electromagnetic field had no direct influence on the reaction pathway. Due to the high chemical resistance of SiC, reactions involving corrosive reagents can be performed without degradation of the vessel material. Examples in- clude high-temperature fluorine–chlor- ine exchange reactions using triethyla- mine trihydrofluoride, and the hydroly- sis of nitriles with aqueous potassium hydroxide. The unique combination of high microwave absorptivity, thermal conductivity, and effusivity on the one hand, and excellent temperature, pres- sure and corrosion resistance on the other hand, makes this material ideal for the fabrication of reaction vessels for use in microwave reactors. Keywords: ceramics · dielectric properties · microwave chemistry · silicon carbide · thermal effusivity [a] B. Gutmann, D. Obermayer, B. Reichart, B. Prekodravac, M. Irfan, Dr. J. M. Kremsner, Prof. Dr. C. O. Kappe Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz Heinrichstrasse 28, 8010 Graz (Austria) Fax: (+ 43) 0316-380-9840 E-mail : oliver.kappe@uni-graz.at Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001703.  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2010, 16, 12182 – 12194 12182