Surfactants weakly basic

Consequently, the SDS microemulsion system is the best model for indirect measurement of log Pow. However, this is valid only for neutral solutes. We reported that the relationship between MI and log Pow for ionic solutes is different from that for neutral solutes (49). This would be caused by the ionic interaction between ionic solutes and the ionic microemulsion as well as ionic surfactant monomer in the aqueous phase. Kibbey et al. used pH 10 buffer for neutral and weak basic compounds and pH 3 buffer for weak acidic compounds (53). Although their purpose was to avoid measuring electrophoretic mobility in the aqueous phase, this approach is also helpful for measuring log Pow indirectly. 

The closeness of fit may be gauged from the experimental and theoretical rate vs. concentration curves for hydrolysis of p-nitrophenyl carboxylates catalysed by quaternary ammonium surfactant micelles (Figure 3). The shape of the curve is satisfactorily explained for unimolecular, bimolecular, and termolecular reactions. An alternative speculative model is effectively superseded by this work. Romsted s approach has been extended in a set of model calculations relating to salt and buffer effects on ion-binding, acid-dissociation equilibria, reactions of weakly basic nucleophiles, first-order reactions of ionic substrates in micelles, and second-order reactions of ionic nucleophiles with neutral substrates. In like manner the reaction between hydroxide ion and p-nitrophenyl acetate has been quantitatively analysed for unbuffered cetyltrimethylammonium bromide solutions. This permits the derivation of a mieellar rate constant km = 6-5 m s compared to the bulk rate constant of kaq =10.9m s . The equilibrium constant for ion-exchange at the surface of the micelle Xm(Br was estimated as 40 10. The... 

Br0nsted coefficients for esterolytic reactivity of anionic nucleophiles in micelles are quite small, so that oximates and hydroxamates are much more reactive than hydroxide ion at a given pH in the weakly basic region. Thus the surfactant (64) is claimed to be the most powerful among functional micelleforming species in promoting the transacylation of p-nitrophenyl acetate and hexanoate. The acyloxime is hydrolysed quite slowly at pH 8, so that catalytic turnover is feeble.Oximate (65) catalyses the hydrolysis of phosphate ester... 

Alkanoylglycamine surfactants are interesting materials having distinctive properties. Their phase behavior suggests that they are more hydrophilic than typical polyoxyethylene surfaetants, but less hydrophilic than other subclasses of nonionic surfactants (semipolar, zwitterionic). They are far less hydrophilic than ionic surfactants. The eompounds are weakly basic—the pKa of protonated dialkyl amides is about 1—so they remain unprotonated and nonionic within the usual pH range. As a result, they do not display the numerous complexities typieally found in ionic compounds. 

The basic Landau-Ginzburg model is valid only for relatively weak surfactants and in a limited region of the phase space. In order to find a more general mesoscopic description, valid also for strong surfactants and in a more extended region of the phase space, we derive in this section a mesoscopic Landau-Ginzburg model from the lattice CHS model [16]. 

Selection of the most suitable organic solvent should consider the polarity of analytes and their association with the surfactant. Solute log Fo/w values can be used, in most cases, as a guide to make this decision.Thus, with SDS as surfactant, a low concentration of propanol ( 1% v/v) is useful to separate compounds with log Po/w < 1 as amino acids. A greater concentration of this solvent ( 5% to 1%) is needed for compounds in the range 1 < log Po/w < 2 as diuretics and sulfonamides. Pentanol ( 2% to 6%) is more convenient for low polar compounds with log Po/w > 3 as steroids. For basic compounds, such as phenethylamines with 0electrostatic interaction between the positively charged solutes and the anionic surfactant adsorbed on the stationary phase. In this case, a high concentration of propanol ( 15%), or preferably, a moderate concentration of butanol (<10%) should be used. 

For the cationic surfactants studied, the excess molar refraction and solute hydrogen-bond acidity contribute positively to K although the effect is small. Solubilizate dipolarity exhibits a weakly negative contribution to and the solubilizate hydrogen-bond basicity a significant negative contribution to K. ... 

The present study focuses on the mechanisms of formation of two dodecylphosphate (DDP) mesostructured alumina synthesized at pH = 5 and 8 respectively. For the material synthesized under acidic conditions, NMR experiments seem to indicate the presence of Al-0-P bonds. The material would be of aluminophosphate type rather than a pure alumina. The sample synthesized under basic conditions contains large amounts of sodium. In this case, the interactions between the surfactant S and the alumina framework 1 are weak and the mechanism of formation would be of S M I° type, where M is the counterion (Na ). 

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