Microwave chemistry
From Wikipedia, the free encyclopedia
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.
MORE synthesis stands for Microwave-organic Reaction Enhancement.
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[edit] Heating effect
- See also: microwave effect
- See also: non-thermal microwave effect
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, e.g. when heating a large sample of ceramic bricks.
Microwave heating is able to heat the target compounds without heating the entire furnace or oil bath, which saves time and energy. It is also able to heat an object throughout the volume (instead of through its outer surface), in theory producing more uniform heating. However, due to the design of most microwave ovens and to absorption by the object being heated, the microwave field is usually non-uniform and localized superheating occurs.
Some compounds absorb microwave radiation differently than others. This selectivity allows some parts of the object being heated to heat more quickly or more slowly than surrounding parts.
Microwave heating can have certain benefits over conventional ovens:
- reaction rate acceleration
- milder reaction conditions
- higher chemical yield
- lower energy usage
- different reaction selectivities
[edit] Selective heating
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.
[edit] References
- ^ 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 DOI:10.1039/b411438h
- ^ Developments in Microwave-assisted Organic Chemistry. C. Strauss, R. Trainor. Aust. J. Chem., 48 1665 (1995).
- ^ Dry media reactions M. Kidwai Pure Appl. Chem., Vol. 73, No. 1, pp. 147–151, 2001. [4]
[edit] External links
- 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
- homepages.uconn.edu/~nil03002 ---> site with microwave equipment and research
