The Effect of Added Salts

At lower ionic strength, 0.1 M, Candau et al. (1988) found a steeper power law than predicted by Cates theory, namely 17 0. This deviation has been attributed to incompletely 

For some surfactant/salt combinations, the dependence of viscosity on added salt concentration is even more peculiar than that shown in Fig. 12-16. Rehage and Hoffmann (1988) found that the zero-shear viscosity of CPyCl has two maxima in viscosity as a 

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Further mechanistic evidence was provided by Benkeser and Krysiak658, who determined the effects of added salts and water on the rates of cleavage of xylyltrimethylsilanes by p-toluenesulphonic acid in acetic acid at 25 °C, the progress of the reaction being followed by dilatometry the first-order rate coefficients are given in Table 227. Clearly the addition of water retards the reaction, as... 

In an earlier series of experiments, Cullis and Ladbury examined the kinetics of the permanganate oxidation of hydrocarbons in acetic acid solution. Initial attack on toluene occurs at the methyl group and a total order of two was found. Electron-withdrawing agents reduced the rate of oxidation. However, the effects of added salts were complex and the authors believe that lower oxidation states of manganese are responsible for the oxidation. The oxidation of ethylbenzene produced acetophenone, the process being second-order with... 

Chevrier et al., 1983), solvent effects (Bensaude et al., 1979), and the effect of added salt on the rate of reaction (Bensaude et al., 1978) have been studied to provide information about this process. Molecular-orbital calculations confirm that a suitable transition state for the reaction is one involving bridging water molecules (Field et al., 1984). 

The effect of added salt on dissolution rate 1s not completely understood at present. A possible explanation of the plateau value 1s that the solubility of the salt in the solid reaches a limiting value at high concentrations. But additional studies are needed to arrive at a quantitative understanding of the observed decreases in CQ and n when salt 1s present. 

Figure 8.10a is an example of some data in which the effect of added salt is more than a competitive ion-binding phenomenon. The reaction involved is the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate, catalyzed by hexadecyl trimethyl ammonium bromide micelles ... 

Figure 8-3 shows the effect of added salt on the solubility of potassium hydrogen tartrate. 

The effects of added salts are shown in Fig. 8. Sodium chloride has a small positive effect on the hydrolysis rate, and sodium chloride and sodium perchlorate have a similar, rather larger, effect on the rate of lactone formation. This is the expected result, for many salts increase the protonating power of the medium as measured by Hammett s acidity function116, and thus assist acid-catalyzed reactions. Sodium perchlorate, unusually, has a small negative effect on the hydrolysis rate. Qualitatively similar results have been found by Bunton et al,56, who studied the effects of added salts on the acid-catalyzed hydrolysis of ethyl acetate. Added lithium and sodium chloride assist the Aac2 hydrolysis of ethyl acetate, but the perchlorates have essentially no effect. In each case the effect is a little more positive than for y-butyrolactone hydrolysis, and, in particular, chloride anions appear to assist Aac2 hydrolysis more effectively than do the perchlorates. 

For the three reactions represented in Fig. 12 the maximum rate of hydrolysis in acid represents only a mpdest acceleration, compared with the rate in initially neutral solution. Bunton and Hadwick89,90 explained the maximum for methyl and phenyl trifluoroacetate in terms of negative salt effects on both acid-catalyzed and neutral reactions. Consistent with this interpretation, it was demonstrated directly that the rate of neutral hydrolysis is decreased by added salts. The effect of added salt should be to decrease the activity of water, and perhaps also to salt in the ester. 

The effect of adding salt to aqueous solutions of a PEO/PBO copolymer has been investigated (Deng et al. 1995), as it has for PEO/PPO Pluronics. Static and... 

The racemisation of ( —)-a-carbethoxybenzylmercuric bromide in DMSO provides not only an example of mechanism SE1, but also the most complete example of the anion-catalysed SE1 mechanism. Ingold and co-workers had briefly investigated the effect of added salts on the rate of racemisation their results are shown in Table 3. In contrast to the mild acceleration or retardation produced... 

The effect of added salts on the rate coefficient for reaction (23) (R = Me) was also studied. Results are collected in Table 23 and show that, whereas sodium perchlorate has a marked accelerating effect (as it does also on the analogous substitution of dimethyldiethyltin), the addition of chloride ion strongly retards the substitution. It was suggested32 that reaction (23) actually proceeds through the solvated Me2Sn2+ ion, formed by the dissociation of dimethyltin dichloride... 

K. Shinoda and H. Takeda, The effect of added salts in water on the hydrophile-lipophile balance of nonionic surfactants the effect of added salts on the phase inversion temperature of emulsions, J. Colloid Interface Sci. 32 (1970) 642-646. 

Figure 17 presents the results of an FTIR spectroscopic study of the effect of salt concentration on the cmt of 70 mM SDS. As Mantsch et al. (4) have shown in similar work with alkali hexadecylsulfates, the cmt can be related to the sudden increase in frequency of the v9 CH2 bands as a function of temperature. The large increase in the gauche conformer content of the methylene chains of the surfactant tails as they "melt" at the cmt is responsible for this frequency shift. The effect of added salt is to raise the cmt of SDS, which is the cause of the "salting out" of this ionic surfactant at any given temperature. The cmt values, taken as the midpoint of the discontinuities in the frequency-temperature plots, agree well with those obtained by other means (14,54). 

Thus gradually it became clear that the role of water in chemical reactions is not straightforward, but the problem of understanding this role was and is extremely difficult. One way of testing hypotheses is to monitor the effects of added salts, neutral solutes and co-solvents on the kinetics of a given reaction. An extensive literature of the effect of added solvents on reactions in water has been built up, particularly by Tommila (1967) and coworkers. In addition, renewed interest was shown in the thermodynamic properties of binary aqueous mixtures, the review by Franks and Ives (1966) of the properties of alcohol + water mixtures... 

The simple model (Fig. 20) can be criticized because it cannot readily be quantified. However, it does account for a wide range of properties, such as the tendency for the partial molar heat capacity and the viscosity -coefficient to become more negative with increase in ion size (Fortier et al., 1974a McDowell and Vincent, 1974 Kay, 1968 1973). Kay has collated conductance and viscosity data and shown how these lead to a classification of ionic properties (Fig. 21). The effects of added salts on the self-diffusion of ions is consistent with the Frank-Wen structural model (Hertz et al., 1974). It is noteworthy that in D20, which is argued to be more... 

Chemical reactions studied in aqueous salt solutions often involve one or more neutral solutes. The question then arises as to the effect that the salts have on these solutes and how in turn the rate of reaction is affected. The effects of added salts on the solubilities of apolar solutes have been extensively studied (Conway and Novak, 1975). The literature up to 1952 was reviewed by Long and McDevit (1952) and more recent data for aqueous solutions documented by Masterson et al. (1971). The information can often be summarized using eqn (23). 

The effect of added salts on the rate constant of a given ionic reaction has been studied for many years. The Br nsted-Bjerrum treatment of these salt effects has been particularly successful, the rate constant being related to the ionic strength of the solution. The observed trends can be quantitatively accounted for using the DHLL or a related expression for the activity coefficients of reactants and transition state. This subject has been reviewed in detail (Perlmutter-Hayman, 1971). The ionic-strength principle appears satisfactory when the reaction involves ions of opposite charge but less so when it involves ions of the same charge. 

Bunn, B.J., Simpkins, N.S., Spavol4 Z., and Crimmin, M.J. 1993b. The effect of added salts on enantioselective transformations of cyclic ketones by chiral lithium amide bases. J Chem Soc Perkin Trans 1, 3113-3116. 

These equations allow the volume change during the micelle-monomer exchange process, the dissociation rate constant for a salt-free system, the effect of added salts on the micelle distribution width a and the dissociation rate constant for the system upon addition of a salt to be calculated [77]. 

Numerous studies have appeared of the effect of added salts on the rates of reaction in solution, and the area has been reviewed (228). The key concept of the activity coefficient of the activated complex affecting the reaction rate was introduced by Brpnsted (34), which led to an expression of the type in Eq. (15), though variations exist. 

McDonald C, Richardson C. The effect of added salts on solubilization by a non-ionic surfactant. ] Pharm Pharmacol 1981 33 38-39. 

A few authors have examined the effect of adding salts on the rate of nitration in sulphuric acid. 

The effect of added salt on the decay rate (ionic strength effect) was determined at pH 3.3 and 9.0. Added salt should increase the rate of reaction between two ions of the same sign to a predictable degree (Reaction 19), and should have little or no effect on the rate of the first-order Reactions 18 and 20. At pH 9, where Reaction 19 does not occur appreciably and the salt effect is governed by Reaction 17, salt increased the decay rate (22) in quantitative agreement with expectation. At pH 3.3, where Reactions 17 and 19 affect the decay rate, no appreciable salt effect was found, again as predicted (29). 

The sulfones, sulfolane and 3-methylsulfolane, are shown to function quite well, as cosurfactants with CTAB, in the solubilization of both organophosphorus esters and betahalosulfides. For the organophosphate used, tributylphosphate, it is shown through pseudo-three-component phase diagrams that the sulfone functions as effectively as the alcohol in its role of cosurfactant. Solubilization of chloroethyl ethyl sulfide is less effective when the sulfone cosurfactant is used, but is still a dramatic enhancement over its solubility in water alone. The effect of added salt on the solubilization is reported, as well as the effect of changes in the surfactant-cosurfactant ratio. Preliminary quasielastic lightscattering measurements are also reported for these unconventional systems. 

Kinetic isotope effects have been measured for hydrogen atom transfer pathways in the photooxidation of various toluenes by photoactivated qui-nones The effect of added salts on the yields of the cation radicals... 

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