Microwave-induced electrostatic etching: generation of highly reactive magnesium for application in Grignard reagent formation.
A detailed study regarding the influence of microwave irradiation on the formation of a series of Grignard reagents in terms of rates and selectivities has revealed that these heterogeneous reactions may display a beneficial microwave effect. The interaction between microwaves and magnesium turnings generates violent electrostatic discharges. These discharges on magnesium lead to melting of the magnesium surface, thus generating highly active magnesium particles. As compared to conventional operation the microwave-induced discharges on the magnesium surface lead to considerably shorter initiation times for the insertion of magnesium in selected substrates (i.e. halothiophenes, halopyridines, octyl halides, and halobenzenes). Thermographic imaging and surface characterization by scanning electron microscopy showed that neither selective heating nor a "specific" microwave effect was causing the reduction in initiation times. This novel and straightforward initiation method eliminates the use of toxic and environmentally adverse initiators. Thus, this initiation method limits the formation of by-products. We clearly demonstrated that microwave irradiation enables fast Grignard reagent formation. Therefore, microwave technology is promising for process intensification of Grignard based coupling reactions.
Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, Laboratory of Macromolecular and Organic Chemistry, Applied Organic Chemistry, P.O Box 513, 5600 MB, Eindhoven, The Netherlands.
Bastiaan H P
BH
van de Kruijs
Mark H C L
MH
Dressen
Jan
J
Meuldijk
Jef A J M
JA
Vekemans
Lumbertus A
LA
Hulshof
D008274:Magnesium / Q000737:chemistry*; D008872:Microwaves; D055672:Static Electricity
D008274:Magnesium