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1 Wiadomości Chemiczne

1 2007

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w słowach kluczowych: synteza organiczna indukowana falami

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Mikrofale w syntezie organicznej

Sawicka M.J., Soroka J.A., Soroka K.B., Gąsiorowska M.

Wiadomości Chemiczne

2007

[Z] 61, 11-12

891-911

The interest in the microwave assisted organic synthesis has been growing during the recent years. It results from an increasing knowledge of fundamentals of the dielectric heating theory, availability of an equipment designed especially for the laboratory use as well as the discovery of the special techniques of the micro-wave syntheses. There are two different mechanisms of transformation of microwave energy into heat. The first one is the dipolar polarization. The electric field of electromagnetic irradiation causes such a change in the polar molecules orientation, that they align their dipole moments with the force field lines. Another way of the microwave - molecule interaction that leads to heat evolution bases on the ionic conduction phenomenon. It originates from a presence of ionic species in the materials. Under the influence of the alternating dielectric field ions start to move through the solution, resulting in an increased collision rate, and the kinetic energy is converted into heat. The microwave activation in organic synthesis leads to considerable acceleration of a chemical reaction as compared to the traditional thermal process. It originates from the thermal effects, i.e. a change of the temperature profile during the process, the existence of so-called "hot spots" and the ability of solvent heating above its normal boiling point as well as the specific (no thermal) effects, connected with a change of the activation energy of the reaction and the activity of molecules. Moreover, microwave irradiation can also change direction, yield and selec-tivity of a chemical reaction. The extent of these changes depends on a solvent pola-rity and polarity of the ground and transition states of reagents. The microwave syntheses are performed in multimode or single-mode cavities, with respect to the mode of the irradiation distribution over the working compartment. The most popular techniques of microwave enhanced syntheses are as follow: syntheses in a solvent, solvent-free syntheses and supported syntheses. The application of one of them depends on the solvent and/or reagents properties as well as the reaction conditions.