Simple solvent

Analytical Supercritical Fluid Extraction and Chromatography Supercritical fluids, especially CO9, are used widely to extrac t a wide variety of solid and hquid matrices to obtain samples for analysis. Benefits compared with conventional Soxhlet extraction include minimization of solvent waste, faster extraction, tunabihty of solvent strength, and simple solvent removal with minimal solvent contamination in the sample. Compared with high-performance liquid chromatography, the number of theoretical stages is higher in... 

In some cases, a simple solvent extraction is sufficient to remove a particular impurity. For example, traces of gallium can be removed from titanous chloride in hydrochloric acid by extraction with diisopropyl ether. 

In the presence of certain cations [sodium, potassium, lithium, calcium, aluminium, chromium, and iron(III)], co-precipitation of the sulphates of these metals occurs, and the results will accordingly be low. This error cannot be entirely avoided except by the removal of the interfering ions. Aluminium, chromium, and iron may be removed by precipitation, and the influence of the other ions, if present, is reduced by considerably diluting the solution and by digesting the precipitate (Section 11.5). It must be pointed out that the general method of re-precipitation, in order to obtain a purer precipitate, cannot be employed, because no simple solvent (other than concentrated sulphuric acid) is available in which the precipitate may be easily dissolved. 

Extraction of the analyte or of the interfering element(s) is an obvious method of overcoming the effect of interferences . It is frequently sufficient to perform a simple solvent extraction to remove the major portion of an interfering substance so that, at the concentration at which it then exists in the solution, the interference becomes negligible. If necessary, repeated solvent extraction will reduce the effect of the interference even further and, equally, a quantitative solvent extraction procedure may be carried out so as to isolate the substance to be determined from interfering substances. 

CHEMICAL REACTIONS IN THE GAS PHASE AND IN SIMPLE SOLVENT MODELS... 

In the previous chapter we considered a rather simple solvent model, treating each solvent molecule as a Langevin-type dipole. Although this model represents the key solvent effects, it is important to examine more realistic models that include explicitly all the solvent atoms. In principle, we should adopt a model where both the solvent and the solute atoms are treated quantum mechanically. Such a model, however, is entirely impractical for studying large molecules in solution. Furthermore, we are interested here in the effect of the solvent on the solute potential surface and not in quantum mechanical effects of the pure solvent. Fortunately, the contributions to the Born-Oppenheimer potential surface that describe the solvent-solvent and solute-solvent interactions can be approximated by some type of analytical potential functions (rather than by the actual solution of the Schrodinger equation for the entire solute-solvent system). For example, the simplest way to describe the potential surface of a collection of water molecules is to represent it as a sum of two-body interactions (the interac-... 

Although the 0-silylation reaction of the tertiary alcohol 1,1-dimethyl-2-phenylethanol (37) with 27 required a reaction temperature of 120 °C and two equivalents of 27, the 0-silyl ether 38 was still obtained in 86% yield by the simple solvent-free procedure. By contrast, the sterically hindered hydroxyl group of 37 was not silylated at all by heating with 27 in DMF at 120 °C for 5 h [8]. 

Using a simple solvent extraction procedure to minimize matrix effects, a diclofop-methyl immunoassay was developed for milk, a number of edible plant products, and other matrices. Gas chromatography (GC) and liquid scintillation counting (LSC) of a C-labeled analyte were used as reference methods to compare with enzyme immunoassay (EIA) results. The methods were well correlated, with comparison of EIA... 

Table 2 gives a summary of results70,71 which provide the solvent number r at which simple solvent loss and charge reduction become competitive. Charge reduction becomes dominant for solvent numbers lower than r. Ion clusters for... 

A facile method for the oxidation of alcohols to carbonyl compounds has been reported by Varma et al. using montmorillonite K 10 clay-supported iron(III) nitrate (clayfen) under solvent-free conditions [100], This MW-expedited reaction presumably proceeds via the intermediacy of nitrosonium ions. Interestingly, no carboxylic acids are formed in the oxidation of primary alcohols. The simple solvent-free experimental procedure involves mixing of neat substrates with clayfen and a brief exposure of the reaction mixture to irradiation in a MW oven for 15-60 s. This rapid, ma-nipulatively simple, inexpensive and selective procedure avoids the use of excess solvents and toxic oxidants (Scheme 6.30) [100]. Solid state use of clayfen has afforded higher yields and the amounts used are half of that used by Laszlo et al. [17,19]. 

Further examples of cavitand-type structures include hw-cyclo-triveratrylene derivatives such as (257) (Gabard Collet, 1981 Canceill, Lacombe Collet, 1986) and the bowl-shaped hosts represented by (258) - the base of the bowl is formed by the four methyl groups. Once again, the shape of these molecules is maintained by conformational constraints. Cavitand (258) is able to accommodate simple solvent molecules such as dichloromethane and chloroform. Moreover, its cavity is large enough to form inclusion complexes with up to four molecules of water (Moran, Karbach Cram, 1982). 

The microorganism Streptomyces halstedii elaborates an antibiotic substance, called carbomycin32 or Magnamycin,33 which has been isolated from the fermentation broth by simple, solvent extraction, and then purified by recrystallization. (Examination of the resulting mother liquors has led to the isolation of a closely similar compound designated as Magnamycin B. 34) Carbomycin has low toxicity,85 and appears to be an effective and satis-... 

The partition of a solute between two immiscible liquid phases provides the basis for simple solvent extraction techniques. The polarity of both solute and solvent are important factors in determining the solubility of the solute, and polar solutes will dissolve more readily in polar solvents than in nonpolar solvents. 

Goldman has studied the effect of nonclassical behavior on the solubility of helium, hydrogen, and neon in simple solvents and benzene (2J3). He has discussed the Henry s constant of water as a solute 24). So far his results do not apply to water as a solvent. 

Fig. 1. Schematic models for ion solvation in simple solvents without ordered bulk [A) and in highly ordered solvents ( )...

We discuss in this section a relatively simple solvent effect that depends only on the size or volume of the particles involved. It will be seen below that since this type of effect depends only on the sizes of the particles and not on any specific interactions between the solutes and the solvent molecules, it may be referred to as the nonspecific solvent effect. ... 

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