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Controlled Microwave Heating in Modern Organic Synthesis

In many small and shallow aquifers the hydrochemistry does not evolve further. However, the baseline natural quality of groundwater may vary spatially within the same aquifer if the mineral assemblages vary, and also evolves with time as the water moves along groundwater flow lines. If an aquifer dips below a confining layer (Figure 2.5), a sequence of hydrochemical processes occurs with progressive distance down gradient away from the outcrop, including precipitation of some solids when relevant ion concentrations reach saturation levels for a solid mineral phase. These processes have been clearly observed in the UK, where the geological history is. | Reviews C. O. Kappe Synthetic Methods Controlled Microwave Heating in Modern Organic Synthesis C. Oliver Kappe Keywords combinatorial chemistry high-temperature chemistry high-throughput synthesis microwave irradiation synthetic methods Angewandte Chemie 6250 2004 Wiley-VCH Verlag GmbH Co. KGaA Weinheim DOI I0.i002 anie.200400655 Angew. Chem. Int. Ed. 2004 43 6250-6284 Angewandte Chemie Microwave Chemistry Although fire is now rarely used in synthetic chemistry it was not until From the Contents Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied to a reaction vessel in a focused manner. The Bunsen burner was later superseded by the isomantle oil bath or hot plate as a source for applying heat to a chemical reaction. In the past few years heating and driving chemical reactions by microwave energy has been an increasingly popular theme in the scientific community. This nonclassical heating technique is slowly moving from a laboratory curiosity to an established technique that is heavily used in both academia and industry. The efficiency of microwave flash heating in dramatically reducing reaction times from days and hours to minutes and seconds is just one of the many advantages. This Review highlights recent applications of controlled microwave heating in modern organic synthesis and discusses some of the underlying phenomena and issues involved. 1. Introduction High-speed synthesis with microwaves has attracted a considerable amount of attention in recent years. 1 More than 2000 articles have been published in the area of microwave-assisted organic synthesis MAOS since the first reports on the use of microwave heating to accelerate organic chemical transformations by the groups of Gedye and Giguere Majetich in 1986. 2 3 The initial slow uptake of the technology in the late 1980s and early 1990s has been attributed to its lack of controllability and reproducibility coupled with a general lack of understanding of the .