Microwave-assisted solvent

MICROWAVE-ASSISTED SOLVENT EXTRACTION AND A NEW METHOD FOR ISOLATION OF TOTAL PETROLEUM HYDROCARBONS (TPH) FROM PLANTS WITH COLUMN CHROMATOGRAPHY (SILICA GEL AND ALUMINA) AND DETERMINATION WITH SPECTROFLUOROPHOTOMETRY... 

Another series of pyrroles, structurally related to amino acids, was obtained in a microwave-assisted solvent-free condensation of a-amino acid methyl esters with chloroenones, which provided the four-carbon unit of the pyrrole. The reaction was carried out by mixing the reagents on silica gel and irradiating for 2-6 min inside a multimode microwave cavity (Scheme 7). The authors reported higher yields and cleaner products when microwaves were used instead of conventional heating [34],... 

MAE simply involves placing the sample with the solvent in specialized containers and heating the solvent using microwave energy. MAE is also sometimes called MASE, which can stand for microwave-assisted solvent extraction or microwave-accelerated solvent extraction. In any event, the extraction process is more rapid than Soxhlet extractions, can be run in batches, and reduces solvent consumption. As in the case of sonication, MAE may overcome retention of the analyte by the matrix, but analyte degradation can be a problem at higher temperatures in certain applications. 

Microwave-assisted solvent extraction is usually carried out in one of the following modes ... 

Applications The broad industrial analytical applicability of microwave heating was mentioned before (see Section 3.4.4.2). The chemical industry requires extractions of additives (antioxidants, colorants, and slip agents) from plastic resins or vulcanised products. So far there have been relatively few publications on microwave-assisted solvent extraction from polymers (Table 3.5). As may be seen from Tables 3.27 and 3.28, most MAE work has concerned polyolefins. 

MAE has also been used for the extraction of adipate plasticisers from PVC [464]. The efficiency of MAE depends on the kind of solvent, the temperature achieved and the heating time. The final temperature reached depends on the microwave power, number of vessels and irradiation time. Higher recovery values than SEE were reported for both phthalate and adipate. Other reports on microwave-assisted solvent extraction have appeared [465-467]. 

Work is in progress to validate the MAE method, proposed for EPA, in a multi-laboratory evaluation study. Nothing similar has been reported for additives in polymeric matrices. Dean el al. [452] have reviewed microwave-assisted solvent extraction in environmental organic analysis. Chee et al. [468] have reported MAE of phthalate esters (DMP, DEP, DAP, DBP, BBP, DEHP) from marine sediments. The focus to date has centred on extractions from solid samples. However, recent experience suggests that MAE may also be important for extractions from liquids. 

Scheme 10.17. Microwave-assisted solvent-free synthesis of 1,3-thiazines.

Scheme 10.19. Microwave-assisted solvent-free domino synthesis of nitrocyclohexanols.

Some early examples involving microwave-assisted solvent-free Sonogashira couplings using palladium powder doped on alumina/potassium fluoride as catalyst were described by Kabalka and coworkers (Scheme 4.4) [150], In addition, this novel catalytic system has been used in microwave-assisted solvent-free Sonogashira coupling-cyclization of ortho-iodophenol with terminal alkynes, and similarly of ortho-ethynylphenols with aromatic iodides, to generate 2-substituted benzo[b]furans... 

Recent advances in the use of Lawesson s reagent include its application in microwave assisted solvent-free syntheses, solid-phase synthesis and combinatorial chemistry.165 Despite the ubiquity of Lawesson s reagent for organic thionation reactions, there are still some classes of compounds that it does not... 

Font N, Hernandez F, Hogendoorn EA, Baumann RA, van Zoonen P. Microwave-assisted solvent extraction and reversed-phase liquid chromatography-UV detection for screening soils for sulfonylurea herbicides. J. Chromatogr. A 1998 798 179-186. 

Pedersen and Lindholst [41] used microwave-assisted solvent extraction followed by SPE to determine octylphenol in liver and muscle of Rainbow trout. 

Paul, S., Gupta, M., Gupta, R. and Loupy, A., Microwave-assisted solvent-free synthesis of pyrazolo [3,4-/7]quinolines and pyrazolo[3,4-c]pyrazoles using p-TsOH, Tetrahedron Lett., 2001, 42, 3827-3829. 

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. 

An alternative solution to the workup issue relied on the attachment of CH-acidic compounds 64 to a soluble polymer support (PEG-4000). The approach improved the yields of the dihydropyrimidinones 66 by the use of a 2-fold excess of other components—urea and aldehyde in the microwave-assisted solvent-free cyclocondensation [118]. Another single-step approach towards 4,5-disubstituted pyrimidines was based on cyclocondensation of a variety of aromatic, heterocyclic and aliphatic ketones, formamide and HMDS as the ammonium source [119]. The high temperature (215 °C) required to effect the formation of pyrimidines was secured by microwave dielectric heating in sealed vessels (Scheme 45). 

Scheme 4 Microwave-assisted solvent-free oxidation of alcohols to carbonyls under various conditions [42-44,47]...

Certain quaternary salts of imidazoles have become important as ionic liquids, in particular salts of l-butyl-3-methylimidazolium (bmim). Preparation of imidazolium-containing ionic liquids, in the desired product ionic liquid as a solvent, is a virtually solvent-free, one-pot process proceeding in good to excellent yields <2003S2626>. There are also microwave-assisted, solvent-free processes for the preparation of imidazolium-based ionic liquids <2001CC643, 2003GC181>. 

Microwave-assisted solvent extraction is another method that uses intensive wave energy to dispense extraction solution to the inner core... 

Shi F, Zhang G, Zhou D et al (2009) An unexpected green and facile synthesis of 2, 6-diaryl-4-styrylpyridines via multi-component reactions in microwave-assisted solvent-free conditions. Chin J Chem 27 1569-1574... 

Mohammadizadeh MR, Hasaninejad A, Bahramzadeh M (2009) Trifluoroacetic acid as an efficient catalyst for one-pot, four-component synthesis of 1, 2, 4, 5-tetrasubstituted imidazoles under microwave-assisted, solvent-free conditions. Synth Commun 39 3232-3242... 

Kumar BRP, Sharma GK, Srinath S et al (2009) Microwave-assisted, solvent-free, parallel syntheses and elucidation of reaction mechanism for the formation of some novel tetraaryl imidazoles of biological interest. J Heterocycl Chem 46 278-284... 

Camel, V. Microwave-assisted solvent extraction of environmental samples. Trends Anal. Chem. 19, 229-248 (2000)... 

Wang LY, Zhang XG, Shi YP et al (2004) Microwave-assisted solvent-free synthesis of some hemicyanine dyes. Dye Pigment 62 21-25... 

Figure 2.21 Some microwave assisted solvent free reactions.

Alternatively, one could use a Soxhlet or similar apparatus to extract the sample. Other methods to prepare a sample for analysis through extraction include supercritical fluid extraction (SFE), pressurized fluid extraction, and microwave-assisted solvent extraction. 

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