Induced Green Synthesis

Normally microwaves have wavelengths between 1 cm and 1 m (frequencies of 30 GHz to 300 Hz). These are similar to frequencies of radar and telecommunications. In order to avoid any interference with these systems, the frequency of radiation that can be emitted by household and industrial microwave oven is regulated, most of the appliances operate at a fixed frequency of 2.45 GHz. 

The preferred reaction-vessel for microwave induced organic reaction, is a tall beaker (particularly for small scale reactions in the laboratory), loosely covered and the capacity of the beaker should be much greater than the volume of the reaction mixture. Alternatively, teflon and polystyrene containers can be used. These materials are transparent to microwaves. Metallic containers should not be used as reaction vessels. 

In microwave induced organic reactions, the reactions can be carried out in a solvent medium or on a solid support in which no solvent is used. For reactions in a solvent medium, the choice of the solvent is very important. The solvent to be used must have a dipole moment so as to absorb microwaves and a boiling point at least 20-30 °C higher than the desired reaction temperature. An excellent solvent in a domestic microwave oven is N,N-dimethylformamide (DMF) (b.p. 160 °C, 8 = 36.7). The solvent can retain water formed in a reaction, thus, obviating the need for water separation. Some other solvents of choice are given as follows  

2- Dichloroethane Ethylene glycol Dioxane Diglyme Triglyme 

Hydrocarbon solvents, for example, hexane (e = 1.9), benzene (e = 2.3), toluene (e = 2.4) and xylene are unsuitable because of less dipole moment and also because these solvents absorb microwave radiations poorly. However, addition of small amounts of alcohol or water to these solvents can lead to dramatic coupling effects. Liquids which do not have a dipole moment cannot be heated by microwaves. By adding a small amount of a dipolar liquid to a miscible non-dipolar liquid, the mixture will rapidly achieve a uniform temperature under irradiation. 

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D. Bandyopadhyay, S. Mukherjee, J.C. Granados, J.D. Short, B.K. Baruk, Ultrasound-assisted bismuth nitrate-induced green synthesis of novel pyrrole derivatives and their biological evaluation as anticancer agents, Eur. J. Med. Chem. 50 (2012) 209-215. 

A synergism between IAA and BR was also described by Katsumi (72) in green cucumber hypocotyl segments, and analysis by the PEST program showed the difference between data sets for IAA alone and IAA with fixed concentrations of BR can be accounted for by a change in the parameter RAMP, suggesting that the response capacity of the tissue to IAA is enhanced by BR (8). Possible explanations for this effect could be increased numbers of receptors for IAA, amplification of the LAA-induced signal, or its transmission, increased transcription or translation rates for LAA-induced protein synthesis, decreased turnover of mRNA or proteins, increased rates of delivery of cell wall components, etc. Much more research is needed to examine these possibilities. 

Green, S.J. and Nacy, C.A., Antimicrobial and immunopathologic effect of cytokine-induced nitric oxide synthesis, Curr. Opin. Infect. Dis., 6, 384, 1993. 

Mekheimer RA, Hameed AA, Sadek KU (2008) Solar thermochemical reactions four-component synthesis of polyhydroquinoline derivatives induced by solar thermal energy. Green Chem 10 592-593... 

Green, S. J., Nacy, C. A., and Meltzer, M. S. (1991). Cytokine-induced synthesis of nitrogen oxides in macrophages A protective host response to Leishmania and other intracellular pathogens. J. Leukocyte Biol. 50, 93-103. 

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