Other Microwave-Assisted Methods

In the view of the above section, it is clearly seen that coupling of hydrothermal method with microwave radiation is widely studied in the literature. In this section, we will shortly discuss some possible combination of microwave heating with other synthesis methods. 

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Scheme 15 Other microwave-assisted methods for the synthesis of imidazoles...

Application of Microwave and Ultrasound Irradiation in the Synthesis of Perovskite-Type Oxides ABO 5.22.2 Other Microwave-Assisted Methods... 

Obviously, some reactions are more suitable than others to be further developed into microwave-assisted methods. The following sections will cover some of the latest efforts made in this area but hopefully this previous section has shown that there are yet many other methods that are transformable into the more high throughput type of chemistry that MAOS can offer. 

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

Overall, microwave-assisted methods are effective approaches in analysis of proteins/peptides, especially when used with other analytical techniques, such as HPLC and MS methods. 

A comparison of mechanosynthesis with other synthetic methods showed the superiority of microwave-assisted method and solution conditions over mechanoehemical and ultrasound reactions for the less-reactive carbodiimides. More-reactive carbodi-imides provide full conversion under aU conditions, while best yields were obtained in MW and solution reactions (entries 6 and 7). 

This microwave-assisted decarboxylation method may have broader applicability as indicated by Aberg et al. who showed two other successful examples of decarboxylations [111]. 

This is a problem that has been reported by several researchers in other cya-nation methods on heteroaromatic halides. (Hetero)aryl chlorides have also been tackled via in situ halogen exchange to (hetero)aryl bromides followed by sequential cyanation (Scheme 71). For this microwave-assisted process an equimolar amount of NiBr2 and a two-fold excess of NaCN were used. The only heteroaromatic chloride tested was 2-chloropyridine. Although the procedures described involve the use of significant amounts of nickel salts, a clear advantage is that the reactions can be performed in air. Moreover, the cyanat-ing reagents are easily removed since they are water soluble. 

Two other examples of microwave-assisted Paal-Knorr reactions were reported in 2004, describing the synthesis of a larger set of pyrroles with different substituents around the ring. The methods differ mainly in the syntheses employed to produce the 1,4 dicarbonyl compounds required for the cyclization. A variation of the Stetter reaction between an acyl silane and dif-... 

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

In recent years, extraction methods for PhACs have usually been based on liquid partitioning with ultrasonic extraction (USE) [43-47], microwave-assisted extraction (MAE) [48], or the more advanced PLE [49-52]. When compared to the other extraction techniques, PLE provides good recoveries, saves time and organic solvent, which makes it become currently a preferred technique for PhAC analyses. 

Carbon-carbon multiple bonds are most commonly reduced to saturated hydro carbons by hydrogenation or by other methods, such as the use of hydrides. While a large number of alkenes have been reduced under microwave irradiation, surprisingly little work has been published on microwave-assisted reduction of alkynes. 

In an attempt to define the exact amount of timesavings associated with the use of microwave-assisted library synthesis, our group devised a method by which the actual control thermal reactions would be performed side-by-side with the microwave reactions by two independent researchers. Furthermore, it was decided that the two scientists would not share experimental results or methodologies so as to not affect each other s research. This series of experiments was labeled the Contest 15. 

Other techniques that have been used to determine polycyclic aromatic hydrocarbons in soil extracts include ELISA field screening [86], micellar elec-tr okinetic capillary chromatography [ 87], supersonic jet laser-induced fluorescence [88,89], fluorescence quenching [90], thermal desorption gas chromatography-mass spectrometry [81,90,100], microwave-assisted extraction [91], thermal desorption [92], immunochemical methods [93,94], electrophoresis [96], thin layer chromatography [95], and pyrolysis gas chromatography [35]. 

Flotron, V., J. Houesson, A. Bosio, C. Delteil, A. Bermond, and V. Camel. 2003. Rapid determination of polycyclic aromatic hydrocarbons in sewage sludges using microwave-assisted solvent extraction. Comparison with other extraction methods. J. Chromatogr. A 999 175-184. 

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