Soft solvents

The application of the HSAB concept to solutions leads to the rule that hard solutes dissolve in hard solvents and soft solutes dissolve in soft solvents (Pearson, 1987). For example, benzene is considered a very soft solvent since it contains only a basic function. Contrary to benzene, water is a very hard solvent, with respect to both its basic and acidic properties, ft is the ideal solvent for hard bases and hard acids. The hardness of water is reduced by the introduction of alkyl substituents in proportion to the size of the alkyl group. In alcohols, therefore, softer solutes become soluble. 

Another property that characterizes solvents is their softness, in terms of the HSAB concept (Pearson 1963), according to which the interactions of soft solvents are strongest with soft solutes, of hard solvents with hard solutes, but are weaker for hard solvents with soft solutes and vice versa. The applicability of the softness property takes into account that it is superimposed on the more general electron pair donation property discussed above. In fact, it can replace (Marcus 1987) the notion of the family dependence of the P scale, expressed by the , parameter (Kamlet etal. 1985). A few quantitative scales have been... 

A solvent softness scale, dependent on the thermodynamics of transfer of ions from water to the target solvent, has been proposed (Marcus 1987). Since soft ions prefer soft solvents and hard ions hard solvents, and since silver ions are soft, whereas sodium and potassium ions are hard, the difference ... 

Iodoacetylenes as well as iodine cyanide are soft Lewis acids (Laurence etal. 1981), which interact with basic solvents yielding characteristic wavenumber shifts Av (C-I) (e g., for ICN relative to the wavenumber in CCI4 solutions). These shifts differ for soft solvents, with sulfur or selenium donor atoms or n systems, and hard solvents, with oxygen or nitrogen donor atoms. However, these authors have not converted this observation and their data to a solvent softness scale. In fact, if prorated values of A v (O-H), for phenol, relative to CCI4 solutions, see B0 H above, representing the hard basicity of the solvents, are subtracted, the remainder measures the solvent softness. Quantitatively,... 

Solvent effects that can be described by an LSER such as Eq. (4.20), but where soft solvents are involved, are better accounted for if a term m i is added (Marcus 1987). 

Inkjet is a commercially driven endeavor, and as such it is often difficult to disentangle the marketing hype from the substance. There are numerous inkjet inks of types described by names meant to indicate that they are healthier to use or have a more benign impact on the environment. Ecosolvents, soft solvents, mild solvents and... 

The soft donor properties of EPD solvents have also been quantified by the softness parameter SP of Gritzner [173, 240]. This parameter is solely based on the standard molar Gibbs energies of transfer of Ag+ ions from benzonitrile as reference solvent to other soft solvents and should be used for soft/soft interactions only. 

The donor properties of soft EPD solvents have also been deseribed by the softness parameter SP of Gritzner [290, 303], This parameter is based on the standard molar Gibbs energies of transfer of soft Ag+ ions from benzonitrile as a referenee solvent to other soft solvents and should only be used for soft solute/soft solvent interaetions. Further solvent softness parameters based on the Raman IR absorption of the symmet-rieal stretehing vibration of the Hg-Br bond in HgBr2 have been developed by Persson et al. [287, 292] cf. also Seetion 3.3.2. The relationships between these solvent softness seales have reeently been reviewed [304]. 

The changes in SCSSD regard the replacement of the permanent dipole moment of each soft solvent sphere by a couple of dipoles, permanent and induced. The permanent dipoles are kept fixed at the orientations minimizing the energy for the solute ground state, while induced dipoles are allowed to be different for each VB structure. A nested iterative procedure is adopted to fix both dipole distributions, and related contribution to the various elements. 

Soft solvents (benzene, acetone, MeaSO) Examples ... 

The saying that like things dissolve each other can be translated in HSAB terms as hard solvents dissolve hard solutes and soft solutes dissolve in soft solvents. 

Softness A further property of solvents that is relevant to their solvation of ions is their softness. The general rule that soft solvents preferably solvate soft ions (Section 2.1.1, Table 2.4) and hard solvents do so for hard ions is valid. Among the solvents on our list, the majority is hard (they have oxygen donor atoms) but a few are soft—pyridine, acetonitrile, tetrahydrothiophene, and these indeed solvate soft cations more strongly than expected from other properties that they have. On the other hand, the solvation of soft anions by the soft solvents is not particularly enhanced. 

Solvents in which an oxygen donor atom has been replaced by a sulfur atom switch from hard to soft solvents. Tetrahydrofuran can thus be compared with tetra-hydrothiophene n = 0.00 and 0.80, respectively. Some other such solvent pairs are 7V,7V-dimethyl-thioformamide ( =1.35) compared to DMF (jU=0.11), N-methyl-thiopyrrolidinone (/<=1.35) compared to NMPy (/t = 0.13), diethylsulfide (fx=0.68) compared to diethylether ( /=0.00), and hexamethyl thiophosporamide (fi = 1.57) compared to HMPT fi=0.29). Solvents with nitrogen and phosphorus donor atoms are also soft, for example, pyrrole (/i=0.81) and aniline ( =0.75) [3]. 

Positive A(G (r, W-> S) values resulted for these cations for transfer into alkanols, acetone, PC, MeCN, Py, MeNO, PhNO, and the dichloroethanes—the cations prefer water over these solvents—and negative values resulted for transfer into the cation-preferred amides, liquid ammonia, DMSO, and TMS that have strong electron pair donor (f)) properties. Exceptions are the soft cations Ag+, Cd ", and Hg + that prefer the soft solvents MeCN and Py. 

The comparison with other scales claimed to represent donor properties of soft solvents is summarized in Table 5.29. The q scale [278] (p. for malakos = soft in Greek) is defined as the difference between the Gibbs energies of transfer of hard sodium and potassium ions from water to a given basic solvent and the corresponding quantity for soft silver ions. 

An example of how the PVDF membrane properties can be engineered through the addition of soft solvent in a dual-bath coagulation system was presented by Thiirmer et al. (2012). As shown in Figure 8.17, when using a single bath with water... 

Charged particles in polar solvents have soft-repulsive interactions (see section C2.6.4). Just as hard spheres, such particles also undergo an ordering transition. Important differences, however, are that tire transition takes place at (much) lower particle volume fractions, and at low ionic strengtli (low k) tire solid phase may be body centred cubic (bee), ratlier tlian tire more compact fee stmcture (see [69, 73, 84]). For tire interactions, a Yukawa potential (equation (C2.6.11)1 is often used. The phase diagram for the Yukawa potential was calculated using computer simulations by Robbins et al [851. 

CO—C H,—CO—0—CHj—CHOH—CHj—OOC—CgH,—CO— These are comparatively soft materials and they are soluble in a number of organic solvents. Under more drastic conditions (200-220°) and with a larger proportion of phthahc anhydride, the secondary alcohol groups are esterified and the simple chains become cross-hnked three dimensional molecules of much higher molecular weight are formed ... 

The most effective Lewis-acid catalysts for the Diels-Alder reaction are hard cations. Not surprisingly, they coordinate to hard nuclei on the reacting system, typically oxygen atoms. Consequently, hard solvents are likely to affect these interactions significantly. Table 1.4 shows a selection of some solvents ranked according to their softness. Note that water is one of the hardest... 

Donor strengths, taken from ref. 207b, based upon the solvent effect on the symmetric stretching frequency of the soft Lewis acid HgBr2. Gutmann s donor number taken from ref 207b, based upon AHr for the process of coordination of an isolated solvent molecule to the moderately hard SbCL molecule in dichioroethane. ° Bulk donor number calculated as described in ref 209 from the solvent effect on the adsorption spectrum of VO(acac)2. Taken from ref 58, based on the NMR chemical shift of triethylphosphine oxide in the respective pure solvent. Taken from ref 61, based on the solvatochromic shift of a pyridinium-A-phenoxide betaine dye. 

TT-Aliylpalladium chloride reacts with a soft carbon nucleophile such as mal-onate and acetoacetate in DMSO as a coordinating solvent, and facile carbon-carbon bond formation takes place[l2,265], This reaction constitutes the basis of both stoichiometric and catalytic 7r-allylpalladium chemistry. Depending on the way in which 7r-allylpalladium complexes are prepared, the reaction becomes stoichiometric or catalytic. Preparation of the 7r-allylpalladium complexes 298 by the oxidative addition of Pd(0) to various allylic compounds (esters, carbonates etc.), and their reactions with nucleophiles, are catalytic, because Pd(0) is regenerated after the reaction with the nucleophile, and reacts again with allylic compounds. These catalytic reactions are treated in Chapter 4, Section 2. On the other hand, the preparation of the 7r-allyl complexes 299 from alkenes requires Pd(II) salts. The subsequent reaction with the nucleophile forms Pd(0). The whole process consumes Pd(ll), and ends as a stoichiometric process, because the in situ reoxidation of Pd(0) is hardly attainable. These stoichiometric reactions are treated in this section. 

Rubber sheeting Rubber, soft Rubber solvent Rubber, synthetic... 

A varnish is often appHed on top of the paint layers. A varnish serves two purposes as a protective coating and also for an optical effect that enriches the colors of the painting. A traditional varnish consists of a natural plant resin dissolved or fused in a Hquid for appHcation to the surface (see Resins, natural). There are two types of varnish resins hard ones, the most important of which is copal, and soft ones, notably dammar and mastic. The hard resins are fossil, and to convert these to a fluid state, they are fused in oil at high temperature. The soft resins dissolve in organic solvents, eg, turpentine. The natural resin varnishes discolor over time and also become less soluble, making removal in case of failure more difficult (see Paint and FINNISH removers). Thus the use of more stable synthetic resins, such as certain methacrylates and cycHc ketone resins, has become quite common, especially in conservation practice. 

Gels. Fluorosihcone fluids with vinyl functionahty can be cured using the platinum catalyst addition reactions. The cure can be controlled such that a gel or a soft, clear, jelly-like form is achieved. Gels with low (12% after 7 d) swell in gasoline fuel are useflil (9) to protect electronics or circuitry from dust, dirt, fuels, and solvents in both hot (up to 150°C) and cold (down to —65° C) environments. Apphcations include automotive, aerospace, and electronic industries, where harsh fuel—solvent conditions exist while performance requirements remain high. 

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