Microwave irradiation for accelerating organic

Account of microwave irradiation for accelerating organic reactions... 

This account provides a summary of a chapter on Microwave Irradiation for Accelerating Organic Reactions in Advances in Heterocyclic Chemistry, volume 90, Part II Six, Seven-membered, Spiro and Fused Heterocycles by E. S. H. El Ashry, A. A. Kassem and E. Ramadan. Microwave irradiation (MWI) has been used extensively in organic synthesis. Application of MWI leads to many advantages, like the use of non-corrosive and inexpensive reagents, in addition to the eco-friendly "green chemistry" economical and environmental impacts. 

General reviews Tierney, J. R. and Lidstrom, R. (Eds), Microwave-Assisted Synthesis , Blackwell, 2005 Microwave irradiation for accelerating organic reactions. Rart I Three-, four- and five-membered heterocycles , El Ashry, E. S. H., Ramadan, E., Kassem, A. A. and Hagar, M., A v. Het-erocycl. Chem., 2005, 88,1 Rart II Six-, seven-membered, spiro, and fused heterocycles , El Ashry, E. S. H., Ramadan, E. and Kassem, A. K,Adv. Heterocycl. Chem., 2006, 90, 1. 

Microwave Irradiation for Accelerating Organic Reactions - Part II Six-, Seven-Membered, Spiro, and Fused Heterocycles... 

El Ashry, E. S. H., Ramadan, E., Kassem, A. A., Hagar, M., Microwave Irradiation for Accelerating Organic Reactions. Part I Three-, Four- and Five-Membered Heterocycles, 88, 1. 

Since the early 2000s, different sources of CO have been explored and applied to carbonylation reactions for laboratory organic synthesis. For example, the use a stoichiometric amount of metal-carbonyl complexes, thermolysis of formic acid at high temperature, and the use of aldehydes via decarbonylation have been investigated. For the use of metal-carbonyl complexes and formaldehyde as carbonyl source, it has been shown that microwave irradiation greatly accelerates the process. ... 

New oxidation reactions of organic substances and the reasons for their acceleration under microwave irradiation have recently been investigated. In particular, in a search for highly efficient oxidation procedures, Chakraborty and Bordoloi [53] used pyridinium chlorochromate (PCC) under the action of microwave irradiation for oxidation of protected a-glucofuranose 62 to the corresponding ketone 63 (99%) much more quickly (10 min) than using the conventional technique (4 h under reflux) (Scheme 12.29) and with an easier work-up procedure. They found the oxidation can also be performed with moist PCC under solvent-free conditions and with the same yield. 

Whereas in the last decade microwave irradiation was mainly applied to accelerate and optimize well-known and established reactions, current trends are indicative of the future use of microwave technology for the development of completely new reaction pathways in organic synthesis. Limited by vessel and cavity size, microwave-assisted synthesis has hitherto been focused predominantly on reaction optimiza-... 

Very recently, a novel microwave-assisted high-temperature UV digestion system for accelerated decomposition of dissolved organic compounds or slurries was developed [95, 96]. The technique is based on a closed, pressurized, microwave decomposition device wherein UV irradiation is generated by immersed electrodeless Cd discharge lamps (228 nm) operated by the microwave field in the oven cavity. The immersion system enables maximum reaction temperatures of up to 250-280 °C, resulting in a tremendous increase in mineralization efficiency. 

Due to the pronounced heating effect of microwave irradiation, most applications refer to in-line sample preparation for the determination of metals in biological and clinical matrices. This approach has also been exploited to accelerate the development of, e.g., hydrolysis, extraction and leaching, as well as for the photo-degradation of organic matter (Table 8.1). 

It is well known that a wide variety of organic reactions are accelerated substantially by microwave irradiation in sealed tubes. These rate enhancements can be attributed to superheating of the solvent, because of the increased pressure generated when the reactions are performed in the a.m. manner. Furthermore several reports have described increased reaction rates for reactions conducted under the action of microwave irradiation at atmospheric pressure, suggesting specific or nonthermal activation by microwaves. Some of these re-studied reactions occur at... 

The main results are compiled in exhaustive reviews [3-7] and books [8-11]. Most of these publications describe important acceleration for a wide range of organic reactions, especially when conducted under solvent-free conditions. The combination of solvent-free reaction conditions and microwave irradiation leads to large reductions in reaction times, enhancements in conversions, and, sometimes [4, 12], in selectivity with several advantages of the eco-friendly approach, termed Green Chemistry . 

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