Hildebrand s solubility parameter

Taken together, these solvent-solute interactions make up the solvent polarity, which is represented well by Hildebrand s solubility parameter (1950). 

The properties of organic liquids relevant to their use as solvating agents have also been reviewed [76]. The ability of liquids to solvate a solute species depends mainly on their polarity and polarizability properties, ability to hydrogen bond, and cohesive electron density. These molecular properties are best measured by the Kamlet-Taft solvatochromic parameters, and the square of Hildebrand s solubility parameter. 

Table 1.5 Cohesive pressures (c), Hildebrand s solubility parameter (5), and internal pressures (n) for a range of representative solvents [1, 2]...

Estimates for Cp were based on Hildebrand s solubility parameters, Sij, (Hildebrand and Scott 1950), which are related to the enthalpy of vaporisation and the... 

From Hildebrand s solubility parameter, heptane is less polar than toluene, which in turn is less polar than methylene chloride, etc., to water, the most polar. Unfortunately, toluene and ethyl acetate exhibit similar 8 which does not account for their chemical properties moreover, Hildebrand s solubility parameters are not known for mixtures. 

In an influential early investigation, correlation of biocatalytic activity data of aerobic and anaerobic whole-cell biocatalysis with solvent properties resulted in the strongest correlation for the partition coefficient log P, whereas both Hildebrand s solubility parameter 6 and the dielectric constant e showed either a weak correlation with activity data or none at all (Laane, 1985,1987) (Figure 12.2). 

Table 10.5 Hildebrand s solubility parameter and cohesive energy density determined from this cohesive energy density from bulk modulus Hydroxyl concentration for some networks, (a) Molar ratio dimethacrylate/ methacrylate = 5 x 10 4 (500 ppm) (b) aromatic poly(bismaleimide) from BASF. 

When the only effects that have to be taken into account are those of cavity formation in the solvent and the dispersion interactions, i.e., when both the solvent and the solute are non-polar, then Hildebrand s solubility parameter concept (Hildebrand and Scott 1950) provides good estimates of the solubility. The mole fraction of a gaseous solute, x2, in a solution in equilibrium at a partial pressure p2 of this gas, can be estimated from the following expression ... 

Hildebrand s solubility parameter 8 = [Av//° - ///]/ V)1/2 is a useful guide for the solubility of nonpolar solutes in nonpolar solvents, but a poor predictor for solubilities in water. In general, the more polar a solvent, or solute, the better it dissolves in water, but again, there is no clear relationship between any... 

Headspace analysis, 151 Hildebrand s solubility parameter, 49, 159 History of chromatography, 1-4 Homologous series plots, 78, 80 Hydrogen bonding, 45, 141... 

Phase separation occurs when AG rises above 0. This may be triggered by a rise in enthalpy (i.e., AH) or a decline in entropy (i.e., AS). To allow for the formation of a uniform network polymer, phase separation must be delayed until crosslinking is well enough advanced to prevent individual molecules from demixing. This delay is achieved by either reducing AH or by raising AS (in concert with T). The enthalpy factor (AH) is controlled by the difference in Hildebrand s solubility parameter (5) between the various reacting components, since... 

The square route of the cohesive pressure is termed Hildebrand s solubility parameter (5). Hildebrand observed that two liquids are miscible if the difference in 5 is less than 3.4 units, and this is a useful rule of thumb. However, it is worth mentioning that the inverse of this statement is not always correct, and that some solvents with differences larger than 3.4 are miscible. For example, water and ethanol have values for 5 of 47.9 and 26.0 MPa°-, respectively, but are miscible in all proportions. The values in the table are measured at 25 °C. In general, liquids become more miscible with one another as temperature increases, because the intermolecular forces are disrupted by vibrational motion, reducing the strength of the solvent-solvent interactions. Some solvents that are immiscible at room temperature may become miscible at higher temperature, a phenomenon used advantageously in multiphasic reactions. 

Sometimes, Hildebrand s solubility parameter 8 has been incorrectly used in linear Gibbs energy relationships cf. for example [96, 97, 226, 255]. Since in linear Gibbs energy relationships the correlated solvent-dependent solute properties e.g. Ig K, Ig k, h v) are proportional to Gibbs energy changes of reaction or activation (AG, AG ) and... 

According to Hildebrand s solubility parameter approach [101], two liquids are miscible if their solubility parameters 8 differ by no more than 3.4 units [101, 102] cf. Eqs. (2-1) and (5-77) for the definition of 8. That is, mutual miscibility decreases as the 8 values of two solvents become farther apart. Higher mutual solubility will follow if the 8 values of the solvents are closer. A comprehensive collection of 8 values has been given by Barton [100]. 

There are many parameters that have been used to describe the attractive forces (dispersive, dipolar and hydrogen bonding) present within a solvent or liquid. However, Hildebrand s solubility parameter (8) is probably the most commonly used. In general, two liquids are miscible if the difference in 8 is less than 3.4 units. Also, if a solid e.g. a polymer) has a 8 similar to the solvent, it will dissolve. However, there are exceptions to this rule especially with polar solvents and solutes. Therefore, it is often worth testing solubility or solvent miscibility on a small scale even if data are available. 

The extraction (and hence the transport) efficiency depends on several diluent factors such as Schmidt empirical diluent parameter [124,125], the Swain s acity and basity parameters along with the Dimroth and Reichardt polarity indices [126], dielectric constant [127], refractive index [127] and viscosity [127], and the Hildebrand s solubility parameter [128]. The permeability coefficients (Paio) were computed from the Wlke-Chang, Scheibel, and Ratcliff [129,130] equations, which compared reasonably well with the experimentally determined values as shown in Table 31.10. Efiiassadi and Do [131] have, on the other hand, taken into account only the viscosity and solubility effect of the diluent and the carrier immobilized in SLM. They have reported that these two factors influenced the transport rates significantly. 

The polarity of the oil can be estimated from Hansen s three-dimensional solubility parameters. Hansen separated Hildebrand s solubility parameter into three independent components < d for the dispersion contribution, polar contribution, and 51, for the H-bonding contribution. As an estimation of the oil polarity, we define Dpi, as the square root of the square of the polar component plus the... 

It is a popular lore that the introduction of some fluorine atoms or a short perfluoroalkyl group results in increasing lipophilicity. A classical parameter 8, Hildebrand s solubility parameter, which is the square root of the cohesive energy density, has been used for miscibility estimation [2]. If two liquids have similar values for 8, i.e. if (Si —S2)2 is small, they are miscible. 

A pump capable of several thousand p.s.i. commonly is used. Not only is the pump needed to maintain supercritical conditions, but the solubilizing power of the system varies greatly with pressure, usually dissolving more solutes as the pressure increases. For example, COj at 1.23 g/em will dissolve eompounds with Hildebrand s solubility parameter (Chapter 41, p. 479) from 7-10, about the same as benzene, chloroform, ethyl acetate, acetone, cyclohexane, carbon tetrachloride, toluene, ethyl ether, and pentane. If the pressure is reduced so that the COj is about 0.9 g/cm then it will dissolve compounds with parameters from 7-9 (solvents like cyclohexane, carbon tetrachloride, toluene, ethyl ether, and pentane) and if further lowered to 0.6 g/cm, it will dissolve only compounds with parameters of 7-8 (ethyl ether and pentane). 

Because the entropy of mixing is nearly always positive, then the AFf term is of overriding importance in determining solubility. Using Hildebrand s solubility parameter, solubility can be expected if the difference between S, and 6 is less than 2 in the absence of H-bonding. 

Why is of the solvent used when determining Hildebrand s solubility parameter ... 

The nature of polymer-solvent interactions plays an important role in deciding the influence of chemical and solvent effects on blends. The Hildebrand s solubility parameter, has been extended to systems that have dispersive (subscript d), polar (subscript p) and hydrogen bonding (subscript h) interactions, i.e., 5, 5p, and 5j, respectively [Hildebrand and Scott, 1949 Burrel and Hansen, 1975]. 

Hildebrand s solubility parameter at 25°C, (cal/cm ) vi = liquid molal volume at superscripted temperature (°C), cmVgmole values in parentheses are for hypothetical liquid. 

For nonpolar solutes, e.g. n-octane, it has been shown that the Gibb s energy of solution in different solvents is linearly correlated with Hildebrand s solubility parameter 8 which takes into account the van der Waals and dispersion forces. In Eq. (58) these forces are considered by the change of the Gibbs energy of evaporation of the solvent. 

A universal approach was developed by Hildebrand who assumed that the mutual solubility of components depends on the cohesive pressure, c. The square root of cohesive pressure is the Hildebrand s solubility parameter, ... 

---