Sodium and potassium decanoate

In a study of pressure effects on sodium and potassium decanoate micelles, the frequency of the CH2 stretching band was found to increase with pressure, with a discontinuous drop at the critical coagelization pressure (75). These results indicate that external pressure applied to micelles induces hydrocarbon tail disordering, even at pressures as high as 20 kbar, followed by a large increase in tail ordering upon coagel formation. 

Clearly, the infrared spectra of the sodium and potassium decanoate micellar solutions are considerably different, as are their pressure dependencies. Since the only difference between these two micellar systems is the size, and thus the charge density of the counterions, the different infrared spectra must be taken as evidence that in the alkali decanoate micelles the sodium or potassium counter cations interact differently with the carboxylate groups of the surfactant molecules. 

Figure 9.3. (a) Experimental solubility curve of decanol in sodium decanoate-water solution at 40 C (27). (b) Calculated solubility curve of decanol in sodium decanoate-water solution at 40°C, obtained with the model developed by Jonsson and co-workers (27). (c) Predicted octanol solubility in potassium decanoate-water solution (28). (Reprinted with permission from the American Chemical Society, copyright 1992)... 

At ambient temperature and pressure the intensity of the vCO band is much higher in the potassium decanoate micelles than in the sodium decanoate micelles. Ihe peak intensity ratio between the vCO and 5CI bands is 1.7 in NaCjo decreases more rapidly with... 

Table 59 presents activation parameters for the decarboxylation of trichloroacetic acid in various basic solvents. Presumably the acid is in the form of its anion in these solvents. The activation parameters fall into a fairly narrow range and the differences presumably represent specific solvation effects. In an acidic solvent, decanoic acid, the activation parameters for the decomposition of potassium trichloroacetate are increased considerably. The values are A/f = 41.4 kcal.mole" and A5 = 27.7 eu . The activation parameters presumably reflect a composite of a prior equilibrium between decanoic acid and the trichloroacetate anion along with decarboxylation of the latter anion. The rate of decarboxylation of sodium nitroacetate is about five times faster in methanol than in water . This effect was attributed to dispersion of the negative charge at the transition state , a process which is more favorable in the less polar methanol solvent. Similarly, the decar-... 

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