Solvent pairs table

The tetrahedral ions of tetraphenylarsonium tetraphenylboride are of comparable structure and size. It is proposed, therefore, that the anion and the cation are similarly influenced on transfer from one solvent to another. This assumption makes it possible to calculate reasonable values for single-ion solvent-transfer activity coelficients (and single-ion Gibbs energies of transfer cf. Table 2-9 in Chapter 2.3) between solvent pairs. Table 5-19 shows some selected values of Ig for anions and cations. These have been... 

In contrast to bilateral triple-ion formation, unilateral triple-ion formation may also occur in solvents of high permittivity, when ion-pair association is increased by noncoulombic specific ion-ion interactions in solvents of low basicity such as PC or AN. Exclusive formation of anionic tripleions [A-C+A-] ", is observed in these solvents when large organic molecular anions A interact with small cations such as Li + or H+. For example, in contrast to lithium acetate in DMSO [97], where ion association is moderate, ion association as well as unilateral triple-ion formation is observed in the solvent PC [105] due to the much lower basicity of this solvent, (see Table 2)... 

Kinetic studies on the nitration of nitrobenzene by nitronium borofhioride in the polar solvents sulphuric acid, methane-sulphuric acid, and acetonitrile show the reaction to be first-order in both nitronium salt and aromatic110. With the first two solvents, the rate coefficients are similar for nitration by nitric acid and by the nitronium salts, indicating a common nitrating entity. With acetonitrile the rate coefficients are very much lower, consistent with a much lower concentration of free nitronium ions in this medium and thus with the nitronium salts existing as ion pairs in organic solvents (see Table 25). 

Values obtained for and a for a number of polymer-solvent pairs are given in Table XXX. It will be observed that the exponent a varies with both the polymer and the solvent. It does not fall below 0.50 in any case and seldom exceeds about 0.80. Once K and a have been established for a given polymer series in a given solvent at a specified temperature, molecular weights may be computed from intrinsic viscosities of subsequent samples without recourse to a more laborious absolute method. 

Co-oxidation was studied for cumene-2-heptylcyclohexanone pair [72] in different solvents (see Table 8.14). The parameters of co-oxidation (rl5 r2, [Pg.340]

The extent of the ionization produced by a Lewis acid is dependent on the nature of the more inert solvent component as well as on the Lewis acid. A trityl bromide-stannic bromide complex of one to one stoichiometry exists in the form of orange-red crystals, obviously ionic. But as is. always the case with crystalline substances, lattice energy is a very important factor in determining the stability and no quantitative predictions can be made about the behaviour of the same substance in solution. Thus the trityl bromide-stannic bromide system dilute in benzene solution seems to consist largely of free trityl bromide, free stannic bromide, and only a small amount of ion pairs.187 There is not even any very considerable fraction of covalent tfityl bromide-stannic bromide complex in solution. The extent of ion pair and ion formation roughly parallels the dielectric constant of the solvents used (Table V). The more polar solvent either provides a... 

Likewise, the following Table 27.1, records the mutual solubilities of a few typical solvent pairs that are used frequently for liquid-liquid extraction procedures. 

As is the case in all other quinine-catalyzed reactions, the quininium-salt-catalyzed phase-transfer reactions are subject to strong solvent effects (Table 8) (81). The fact that, in the presence of water, polar solvents lower the e.e., whereas apolar solvents raise the e.e., indicates that these are true phase-transfer reactions in which the ion pairs within the organic layer are responsible for the asymmetric induction. 

Table 4.2 summarises a selection of solvent pairs that are sufficiently immiscible to form biphasic mixtures suitable for LLE. Klick used LLE as one step in a method to measure an epoxide degradant of a pharmaceutical [12]. In an application of SEC to environmental analysis, LLE was found to give higher extraction efficiencies than solid-phase extraction (SPE - see below) [29]. 

The diad fractions have been determined as a function of polymerization temperature for many vinyl and acryl polymers. Many values of (AH. — Aff ) and (AS. — A) can thus be calculated (see the compilation of Elias and Goeldi for 85 monomer/solvent pairs). It is interesting that many negative differences (AS. — ASf/8 ) can be found for a given system monomer/solvent (Table III), but only a few negative values of (AH, . — AHf/g). Most negative is the (A— AHf/g ) for the polymerization of vinyl chloride in bulk (see Table II). All other values of (AH. — AH /g) are higher than zero or at least nearly zero. 

Table I lists the final results of solvent-swelling conditions which resulted in selecting 2,2,4-trimethylpentane and styrene at —25°C for a differential solvent pair. The table also includes the published values for the solubility parameters (a/CED) of the elastomers and the solvents. This table indicates that for the elastomer systems Cl-butyl-cts-polybutadiene or Cl-butyl-SBR excellent differentiation can be obtained.

Solvent pairs selected from the extremes of the list Table 2.8 are not usually sufficiently miscible to be satisfactory, e.g. methanol and light petroleum. 

Although solvents may form two visibly distinct phases when mixed together, they are often somewhat soluble in each other and will, in fact, become mutually saturated when mixed with each other. Data on the solubility of various solvents in water (Table 2.2) and on the solubility of water in other solvents (Table 2.3) should be consulted when selecting an extraction solvent pair. For example, 1.6% of the solvent dichloromethane (or methylene chloride) is soluble in water. Conversely, water is 0.24% soluble in dichloromethane. According to Table 2.3, when the phases are separated for recovery of the extracted analyte, the organic solvent layer will contain water. Similarly, according to Table 2.2, after extraction the depleted aqueous phase will be saturated with organic solvent and may pose a disposal problem. (Author s note I previously recounted [43] my LLE experience with disposal of extracted aqueous samples that were cleaned of pesticide residues but saturated with diethyl ether. Diethyl ether is 6.89% soluble in water at 20° C.)... 

In LC there is a relatively small number of stationary phase packing materials available. Therefore, it is necessary to vary solvent polarities to separate materials with vastly different k values. Often this guidance comes from the tabulation of the physical properties of the solvents (Table 6-3). In addition to polarity of the final mobile phase, there are two additional major considerations when selecting solvent pairs for either isocratic or gradient... 

Mixed Solvents Effect. Using mixed solvents can improve selectivity. For example, adding small amounts of water has improved the selectivity of furfural in separating C4 hydrocarbons (24). Baumgarten and Gerster (25) have studied how various solvents affect the selectivity of furfural for the pentane-pentene pair. They concluded that for only a few solvents some improvement was observed. The resulting selectivity lies between the selectivity of the pure solvents (see Table III). To avoid immiscibility at high solvent concentrations, a second solvent is sometimes added (25). 

Suitable common solvent pairs from the solvents given in Table 13.1 are water/ethanol and dichloromethane/light petroleum (b.pt. 40-60 °C), but many other combinations are possible. One of the most frequently encountered mixed solvent systems is aqueous ethanol (water/ethanol) in which the compound to be recrystallized is insoluble in water and very soluble in ethanol. 

The mathematical form of equations 7 and 8 suggest that errors will diminish as diflFerences in the magnitude of thermal diflFusion between homopolymers and between solvents increase. Because thermal diflFusion is comparable in toluene and THF but significantly diflFerent (weaker) in cyclohexane, we substituted cyclohexane for THF and reanalyzed the copolymer. The results are displayed in Table III. The estimated composition is 56 mole percent styrene in this solvent pair, which is still within the uncertainty of the nominal value. The estimated molecular weight remains 13% high. However, with a 4% adjustment in Dt values, the estimated molecular weight matches the nominal value. 

A treatment of the propagation of errors in the toluene-cyclohexane system is summarized in Table IV and Figure 5. In this solvent pair, the... 

Solvent Pairs. To use a mixed solvent dissolve the crystals in the better solvent and add the poorer solvent to the hot solution until it becomes cloudy and the solution is saturated with the solute. The two solvents must, of course, be miscible with each other. Some useful solvent pairs are given in Table 2. 

Typical applications of reversed-phase chromatography are shown in Table 2. Beyond analytical apphca-tions, RP-TLC on bonded phases is also a tool for physicochemical measurements, particularly for molecular hpophilicity determination of biologically active compounds. Hydrophobicity can be measured by partition between an immiscible polar and nonpolar solvent pair, particularly in the reference system n-oc-tanol-water. The partition coefficient, P, is frequently used to interpret quantitative structure-activity relationships (QSAR studies). 

Sometimes the mutual solubility of a solvent pair of interest can easily be decreased by adding a third component. For example, it is common practice to add water to a solvent system containing a water-miscible organic solvent (the polar phase) and a hydrophobic organic solvent (the nonpolar phase). A typical example is the solvent system (methanol + water) + dichloromethane. An anhydrous mixture of methanol and dichloromethane is completely miscible, but adding water causes phase splitting. Adjusting the amount of water added to the polar phase also may be used to alter the K values for the extraction, density difference, and interfacial tension. Table 15-5 lists some common examples of solvent systems of this type. These systems are common candidates for fractional extractions. 

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