The cleaning of solvents and reagents

Another way of ensuring that a glass surface is free of water or hydroxyl groups is to cover it with a film of sodium. This method was used when the melting point phase diagram for the system isobutene + titanium tetrachloride was determined (Longworth, Plesch and Rutherford, 1959 Plesch, 1972), but it cannot be used on silane-treated glass as the sodium will not spread on the waxy surface. 

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The preparation of a combinatorial library requires the simultaneous manipulation and isolation of many different compounds. A uniform sequence of operations is required to efficiently prepare and isolate each member of the library. In contrast the traditional synthesis of compounds utilizes conditions tailored specifically to the compound desired. A key challenge for library preparation is the development of a robust synthesis sequence that cleanly incorporates chemical building blocks containing a diverse range of chemical functionality in high yields. Equally important are the development of uniform and efficient methods to isolate intermediates and products from solvents, reagents, and byproducts. 

Avoiding the use of organic solvents during MAOS of heterocycles lead to a clean, efficient and economical technology (Green Chemistry). Apart from this the safety is increased, workup is considerably simplified, cost is reduced, the use of toxic solvents can be avoided and the reactivities and sometimes the selectivities can also be enhanced without dilution. Due to these positive aspects of solvent free synthesis, there is a marked increase in the use of environmentally benign reagents and procedures. 

Solvents and Reagents. All solvents used in this study were Burdick and Jackson Distilled in Glass. The diethyl ether used was ethanol-free, available from B J on special order. The XAD-2 resins used for sampling the seawater suspensions were purchased from Supelco, Inc., and cleaned by soxhlet extraction according to the method of Junk et al. (17). 

SFE has been demonstrated to be a good extraction technique for A-nitrosamines in rubber products. In addition, SFE allows fast analysis with a reduction in solvent waste, time, and manipulation. Although recoveries are not too good, especially for the smaller A-nitrosamines, SFE could be considered as a useful tool to determine these analytes, considering that through its selectivity it provides quite clean extracts in one step." Reche et al." determined A-nitrosamines in latex products by combining supercritical fluids and chemical derivatization. The addition of a denitrosation reagent into the extractor combined with an adequate liquid trap allows elucidation of the presence of A-nitrosamines as well as their potential precursors. 

A variety of olefinic hydrocarbons have been dimetallated [1]. Most of the papers on this subject have been published by the groups of Klein and Bates. The usual base-solvent systems for the dimetallations are BuLi TMEDA-hexane and BuLi t-BuOK in hexane or homologues. In practice, clean dimetallations are not easily realizable. The result is very often a mixture of the mono- and dimetallated hydrocarbon and after reaction with some electrophilic reagent a corresponding mixture of mono- and disubstituted product is obtained. Examples of dimetallation reactions with preparative significance are the formations of the following species ... 

Vessels should be cleaned very carefully to avoid contamination. Solvent and reagent blanks should be made with each new batch of products and each analytical series of samples. Blanks and recoveries should be determined under the same circumstances as the analyte contents... 

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