Microwaves in Organic and Organometallic Synthesis

This study shows that chemical reactions in polar solvents can be carried out rapidly and conveniently using microwave heating in sealed Teflon containers. Reactions of organic and or ganometallic compounds are reported, and rate enhancements of up to 1,240 times have been observed. The acceleration of reactions (compared to normal reflux conditions)oc curs because the increased pressure developed in the reaction vessels causes superheating of the solvent. The rate of absorption of microwave radiation is affected by the polarity and the volume of the reaction mixture. The heating rate is also influenced by the presence of ions in solution.The yields of relatively slow reactions can be increased by programming the power levels of the microwave oven. This technique allows the reactions to be carried out more safely and to be scaled up to some extent. Microwave heating results in considerable energy savings compared with conventional heating methods. The energy efficiency can be further increased by power programming.Microwave heating has not been found to alter the composition of products of a chemical reaction appreciably. While small differences in product ratios are observed in reactions carried out under microwave and conventional heating, this appears to be merely a thermal effect and can be attributed to the higher temperatures achieved in microwave reactions.