Microwave chemistry is the science of applying microwave irradiation to chemical reactions . Microwaves act as high frequency electric fields and will generally heat anything with a mobile electric charge. Polar solvents are heated as their component molecules are forced to rotate with the field and lose energy in collisions. Semiconducting and conducting samples heat when ions or electrons within them form an electric current and energy is lost due to the electrical resistance of the material. Heating a reaction or chemical reactor by microwave radiation (as seen in a domestic microwave oven) has a number of advantages over conventional heating;

• The heat is formed directly and rapidly in the sample.
• Energy is not wasted in heating furnaces or oil baths.
• The entire volume of the reactor can be heated (virtually) uniformly.
• Selected volumes of the sample (including microscopic regions) can be selectively heated.

Conventional heating usually involves the use of a furnace or oil bath, which heats the walls of the reactor by convection or conduction. The core of the sample takes much longer to achieve the target temperature (Particularly when heating a large sample of ceramic bricks, for example. Rapid and homogeneous heating has the following benefits:

• reaction rate acceleration
• milder reaction conditions
• higher chemical yield
• lower energy usage

Some of these effects are derived from superheating or hot spots, well known effects in microwaving.

Selective heating is particularly important in the microwave heating of supported metal catalysts. A specific application in synthetic chemistry is in the microwave heating of a binary system comprising a polar solvent and an apolar solvent obtain different temperatures. Applied in a phase transfer reaction a water phase reaches a temperature of 100°C while a chloroform phase would retain a temperature of 50°C. Microwave chemistry is particularly effective in dry media reactions.

See also

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Microwave effect

Non-thermal microwave effect

References

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1. Microwaves in organic synthesis. Thermal and non-thermal microwave effects, Antonio de la Hoz, Angel Diaz-Ortiz, Andres Moreno, Chem. Soc. Rev., 2005, 164-178
2. Developments in Microwave-assisted Organic Chemistry. C. Strauss, R. Trainor. Aust. J. Chem., 48 1665 (1995).
3. Dry media reactions M. Kidwai Pure Appl. Chem., Vol. 73, No. 1, pp. 147–151, 2001. ^*

External links

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• AMPERE (Association for Microwave Power in Europe for Research and Education)
• Microwave Chemistry Pages --> Comprehensive introduction to "microwave chemistry"
• MAOS (Microwave-Assisted Organic Synthesis) --> General web resource guide of "microwave chemistry"
• Microwave Synthesis @ organic-chemistry.org
• www.microwavechemportal.org ---> information portal for Microwave-assisted chemistry and researchers working in this expanding field

Instrument suppliers homepages

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• Biotage AB
• CEM
• Anton Paar
• Milestone

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