Chemistry Using Microwaves

Principles and Characteristics Pare et al. [475] have patented another approach to extraction, the Microwave-Assisted Process (MAP ). In MAP the microwaves (2.45 GHz, 500 W) directly heat the material to be extracted, which is immersed in a microwave transparent solvent (such as hexane, benzene or iso-octane). MAP offers a radical change from conventional sample preparation work in the analytical laboratory. The technology was first introduced for liquid-phase extraction but has been extended to gas-phase extraction (headspace analysis). MAP constitutes a relatively new series of technologies that relate to novel methods of enhancing chemistry using microwave energy [476]. 

Heterocyclic chemistry using microwave-assisted approaches... 

HETEROCYCLIC CHEMISTRY USING MICROWAVE-ASSISTED APPROACHES... 

Besson T, Brain CT (2004) Heterocyclic Chemistry Using Microwave-Assisted Approaches. In Lidstrom P, Tierney JP (eds) Microwave-Assisted Organic Synthesis. Blackwell, Oxford, p 44... 

Although use of Boc has enabled successful syntheses, its application has been limited, because of the use of HF - a major factor in the current preference for Fmoc chemistry [6]. Little known work has been performed with Boc chemistry using microwave energy. For this reason, this chapter focuses on the application of microwave energy for Fmoc SPPS. 

Ereeman, R. G. McCurdy, D. L. Using Microwave Sample Decomposition in Undergraduate Analytical Chemistry, ... 

The description of the association of heterocychc chemistry and microwave irradiation has also shown that performing microwave-assisted reactions should be considered with special attention. A few of these considerations can be applied generally for conducting microwave-assisted reactions and include the following (a) the ratio between the quantity of the material and the support (e.g., graphite) or the solvent is very important (b) for solid starting materials, the use of solid supports can offer operational, economical and environmental benefits over conventional methods. However, association of liquid/solid reactants on solid supports may lead to uncontrolled reactions which may result in worse results than the comparative conventional thermal reactions. In these cases, simple fusion of the products or addition of an appropriate solvent may lead to more convenient mixtures or solutions for microwave-assisted reactions. 

Abstract An overview on the microwave-enhanced synthesis and decoration of the 2(lH)-pyrazinone system is presented. Scaffold decoration using microwave-enhanced transition-metal-catalyzed reactions for generating structural diversity, as well as the conversion of the 2(lH)-pyrazinone skeleton applying Diels-Alder reactions to generate novel heterocyclic moieties are discussed. The transfer of the solution phase to polymer-supported chemistry (SPOS) is also described in detail. 

R. S. Varma, PureAppl. Chem. 2001, 73, 193-198 R. S. Varma, Tetrahedron 2002, 58, 1235-1255 R. S. Varma, Advances in Green Chemistry Chemical Syntheses Using Microwave Irradiation, Kavitha Printers, Bangalore, 2002. 

A. Loupy, A. Petit, J. Hamelin, F. Texier-Boullet, P. Jacquault, D. Mathe, Synthesis 1998,1213-1234 R. S. Varma, Green Chem. 1999, 43-55 M. Kidawi, Pure Appl. Chem. 2001, 73, 147-151 R. S. Varma, Pure Appl. Chem. 2001, 73,193-198 R. S. Varma, Tetrahedron 2002, 58,1235-1255 R. S. Varma, Advances in Green Chemistry Chemical Syntheses Using Microwave Irradiation, Kavitha Printers, Bangalore, 2002. 

Our main motivation for writing Microwaves in Organic and Medicinal Chemistry derived from our experience in teaching microwave chemistry in the form of short courses and workshops to researchers from the pharmaceutical industry. In fact, the structure of this book closely follows a course developed for the American Chemical Society and can be seen as a compendium for this course. It is hoped that some of the chapters of this book are sufficiently convincing as to encourage scientists not only to use microwave synthesis in their research, but also to offer training for their students or co-workers. 

An efficient solventless synthesis of imidazolones via the Knoevenagel reaction using microwave irradiation has appeared recently in Green Chemistry [76] (Scheme 8.52). 

In an additional application of fluorous chemistry, radical-mediated cyclizations were performed in benzotrifluoride using microwave irradiation [70]. In the pre-... 

PANFILI G, MANZI P, COMPAGNONE D, SCARCIGLIA L and PALLESCHI G (2000), Rapid assay of chohne in foods using microwave hydrolysis and a choline biosensor , J Agric Food Chem, 48, 3403-7. pant I and trennery v c (1995), The determination of sorbic acid and benzoic acid in a variety of beverages and foods by micellar electrokinetic capillary chromatography , Food Chem, 53(2), 219-26. pare j r j and Belanger j m r (1997), Instrumental Methods in Food Analysis. Series Techniques and instrumentation in analytical chemistry - Vol. 18, Amsterdam, Elsevier. 

Each step of the synthesis usually needs optimisation of reaction conditions (time, temperature, solvents, concentrations). Different techniques of reaction activation can also be used. Microwave heating has been shown to give faster, cleaner and more selective reactions [22,23] than conventional heating. Ultrasound, although promising [24], has not known the same development. Finally, catalysed reactions involving palladium complexes have been developed in car-bone- 11 chemistry [25 ] over the last few years. They have not been widely studied in fluorine-18 chemistry. 

Carbonylation reactions with microwave irradiation have been investigated in connection with solid-state combinatorial chemistry.Since reactions requiring gaseous reagents cannot use microwave irradiation, metal carbonyl complexes, such as Mo(CO)6, Cr(CO)6, W(CO)6, and Co2(CO)8 have been employed as source of carbon monoxide. " Examples of aminocarbonylation performed with microwave irradiation are presented in Section 11.15.4.3 (vide supra). 

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