Microwave Technique for Synthesis Organic Compounds

Dr.Nadia Sadiq Majeed

Department of Chemistry

    In organic chemistry, one of the very current styles is microwave-assisted organic synthesis (MAOS). Many types of organic reaction examined successfully in microwaves (MWs) for preparation of heterocyclic compounds, pharmaceutical, carbon material, solid-phase peptide synthesis and nanoparticles because reduction of reaction time for days and hours to minutes and seconds, improvement of the purification and development of product yield, all these reasons increase to money and time saving and useful to the environment.

         The first microwave oven was presented in 1955 by Tappan but the common use of microwave ovens happened through the 1970 and 1980 while the first application of microwave irradiation in 1986 used for chemical synthesis.

A microwave (MWI) is a form of electromagnetic energy, the two mechanism for transferring energy from microwave to the material are ionic conduction and dipole rotation therefore only polar molecules transfer energy rapidly and absorb microwave irradiation very well but non-polar molecules are inert to microwave dielectric loss, also the boiling point values when solvents are used in microwave irradiation conditions are higher than with conventional heating . This effect, called the ” super heating effect”’ There are two general classes of microwave effects in organic chemistry :

1. Specific microwave effects are those effects that cannot be easily emulated through conventional heating methods such as :

2. Rapid heating rates and temperature gradients.

3. The elimination of wall effects.

4. Selective heating of specific reaction components.

5. Non-thermal microwave effects have been proposed in order to explain unusual observations in microwave chemistry as the name suggests, the effects are supposed not to be require the transfer of microwave energy in to thermal energy.

  we have used MWI for synthesis of different target compounds. This technique is useful for reducing reaction times to minutes and seconds from days and hours .    Not only is direct microwave heating able to reduce chemical reaction times from hours to minutes, but it is also known to reduce side reactions, increase yield and improve reproducibility^. .Therefore, many academic and industrial research groups are using ( MAOS) as forefront technology for rapid reaction optimization, for the efficient synthesis of new chemical entities or for discovering and probing new chemical reactivity. Microwave irradiation is electromagnetic irradiation in the frequency 0.3-300 GHz  . All domestic microwave ovens and all dedicated microwave reactors for chemical synthesis operate at a frequency of  2.45 GHz to avoid interference with telecommunication and cellular phone frequencies . Microwave – enhanced chemistry is based on the efficient heating of materials by microwave dielectric heating effects. Microwave dielectric heating is dependent on the ability of a specific material like solvent or reagent to absorb microwave energy and convert it into heat .The electric component of an electromagnetic field causes heating by two main mechanisms: dipolar polarization and ionic conduction