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Workup techniques

The first choice for a solvent during the development of a synthetic procedure is usually an organic liquid, which is selected on the basis of its protic or aprotic nature, its polarity, and the temperature range in which the reaction is expected to proceed. Once the desired transformation is achieved, yield and selectivity are further optimized in the given medium by variation of temperature, concentration, and related process parameters. At the end of the reaction, the solvent must be removed quantitatively from the product using conventional workup techniques like aqueous extraction, distillation, or chromatography. If the synthetic procedure becomes part of a large-scale application, the solvent can sometimes be recycled, but at least parts of it will ultimately end up in the waste stream of the process. [Pg.81]

The need to implement green chemistry principles (e.g., safer solvents, less hazardous chemical synthesis, atom economy, and catalysis) is a driving force toward the avoidance of the use of toxic organic solvents. A solvent-free or solid-state reaction obviously reduces pollution and reduces handling costs due to simplification of experimental procedure and workup technique and savings on labor. However, interest in the environmental control of chemical processes has increased remarkably in the last three decades as a response to public concern about the use of hazardous chemicals. Therefore, to improve the effectiveness of this method in preventing chemical waste, it is important to investigate its optimal conditions. [Pg.68]

An important breakthrough in that respect was the use of soHd-phase organic synthesis (SPOS) where the attachment of the substrate to an insoluble support allowed for easy workup (filtration) and for rapid generation of products via split-mix procedures [1,2]. An important subsequent development consisted of the immobihzation of reagents, scavengers and catalysts. This technique, coined polymer-assisted solution phase chemistry (PASP), allowed solution phase synthesis of compoimds, yet still enjoying the bene-... [Pg.130]

Tzschucke, C.C., Markert, C., Bannwarth, W., Roller, S., Hebei, A. and Haag, R. (2002) Modern separation techniques for the efficient workup in organic synthesis. Angewandte Chemie International Edition, 41 (21), 3964-4000. [Pg.85]

Table 11,1.1 contains a workup of the data in terms of the above analysis. In the more general case one should be sure to use appropriate averaging techniques or graphical integration to determine both F(t) and T. When there is an abundance of data, plot it, draw a smooth curve, and integrate graphically instead of using the strictly numerical procedure employed above. [Pg.392]

However, pyrolysis is rapid, avoids sample wet chemical workup, avoiding sample loss and contamination, and has a low sample requirement. It allows the determination, in a single step, of polymeric materials (with in situ hydrolysis of the hydrolysable polymers and thermal decomposition of the nonhydrolysable polymers) and low molecular weight components [16]. As a result, pyrolysis is a relatively fast and inexpensive technique, especially if compared with the classical wet analytical procedures that are required prior to GC/MS analyses. [Pg.306]

Initial workup for a woman presenting with a localized lesion or suggestive symptoms should include a careful history, physical examination of the breast, three-dimensional mammography, and, possibly, other breast imaging techniques such as ultrasound. [Pg.692]

We have suggested that separation strategies be planned with the following goal in mind the target product(s) in a final reaction mixture should partition into a phase that is different from all the other components of the mixture.181 When this goal is met, reactions can be purified simply by workup, which involves simple phase separation techniques such as evaporation, extraction, and filtration. [Pg.27]

Other techniques to improve throughput are instrumentation based and may involve multiple HPLC systems. The simplest method involves the automated use of solid phase extraction cartridges for sample cleanup followed by direct injection into the mass spectrometer [114], Coupling of multiple HPLC systems to one mass spectrometer allows one column to equilibrate and separate while another column to flow into the mass spectrometer. Multiple HPLC systems may be configured such that the mass spectrometer is only exposed to each serial HPLC eluent as the analyte of interest is eluted [115,116]. Although multiple H P LC-based methods may increase throughput, they also typically decrease sensitivity and may confound data workup and interpretation. [Pg.205]

In general, solid-phase synthesis, rather than solution-phase synthesis, can be the preferred method for the generation of combinatorial libraries because of the greater abihty to automate a solid-phase protocol, primarily due to the use of excess reagents in solution to effect cleaner reactions and to the ease of workup by simple filtration. The solid-phase method of peptide synthesis has had many notable successes. However, the preparation of peptides containing more than 20 amino acids in length using the solid-phase technique often causes major problems in that very extensive purification of the final product is needed. [Pg.182]

The assessment of mutagenic activity in cooked foods requires tedious extraction work in order to isolate and quantify the responsible chemicals at the nanogram level. Efforts have been made to develop a rapid and efficient method to obtain chromatograms free of interfering material. Coextracted matrix components influence analyte detection limits more than does absolute detector sensitivity (182). The sample workup therefore is the most critical part of the analysis (183). Solid-phase extraction with different coupled columns provides an improvement (176) over LLE and the use of large columns filled with XAD resin. The determination of PAHs and PANHs in food has been carried out by different chromatographic techniques, including LC with fluorescence (164,171,184) and/or UV detection (185,171) and GC with FID (168,186) or MS detection (187). [Pg.897]

The performance and scalability of the various techniques is most easily compared in a side-by-side format. With respect to experimental procedures, it is now recognized that many chemical conversions (e.g., formation of C-N or C-C bonds) that were reported to require solid supports with catalytic activity and microwave irradiation (and thus introduced environmental concerns) do not require such auxiliaries or irradiation. They occur exothermally at low temperatures with quantitative yields and without solvent-consuming workups even on a large scale. [Pg.439]

An extended application of the resin-capture-release technique is depicted in Scheme 13. With the help of reagent 31, a functionalized pyridine was captured as an acyl pyridinium cation 32 on a solid support which was followed by Grignard addition and hydrolysis under acidic conditions to afford polymer-supported N-acylated dehydropyridinones 33 [39]. Advantageously, any unreacted acylium complex collapses to the parent resin upon workup. These heterocycles, which ideally can serve as scaffolds, are then released under basic conditions. [Pg.273]


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See also in sourсe #XX -- [ Pg.175 , Pg.176 , Pg.177 ]




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