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The base dissociation of ammonia has been studied by an ultrasonic absorption method in both the absence and presence of SDS micelle in aqueous solution, and kinetic parameters were obtained. The micellar catalyzed reaction mechanism, including the interactions of ammonium ion with SDS micelles, are discussed.

Ultrasonic absorption was measured in hexane solutions of octylammonium alkanoates (nonanoate, decanoate, dodecanoate, and tetradecanoate). The value of critical micelle concentration (CMC) was determined to be 0.02 M (1 M=1 mol dm−3) for all the surfactants. The excess ultrasonic absorption, observed in the solutions above the CMC, was ascribed to the association-dissociation of the monomer to and from the micelle. From the concentration dependences of the ultrasonic parameters, the mean aggregation number of the micelle, the rate constants, and the enthalpy change of the above reaction were obtained. These results were discussed in relation to the shape of the reversed micelle and the solute-solvent interactions.

Micellar catalytic effects on the base dissociation of methylamine have been studied by ultrasonic absorption method. The dissociation constant, the rate constants, and the volume change of the reaction were obtained in the absence and in the presence of SDS. The micellar catalytic effects observed for methylamine was smaller than those for amines of long alkyl chain, which was ascribed to the facts that the former is incorporated into the micellar ionic atmosphere in the concentrated micellar solution while the latters are solubilized into micelles.

The ultrasonic relaxation absorption has been measured in aqueous solution of dipentylamine, dihexylamine, dioctylamine, N-methylphenethylamine, and N-ethylbenzylamine in the presence of the sodium dodecyl sulfate(SDS) micelle. The relaxation absorption has been ascribed to the base equilibrium of the amines on the surface of the micelle: RR′NH2++OH−\oversetkf\undersetkb\ightleftharpoonsRR′NH+H2O. The rate constants γ±2kf, kb, the apparent base dissociation constant Kb (=kb⁄γ±2kf), and the volume change in the base equilibrium ΔV were obtained, where γ± is the mean activity coefficient for RR′NH2+ and OH−. The dependence of the rate constants on Kb revealed that, in the detailed mechanism of the base equilibrium of the amines, RR′\underset(I)NH2++OH−\oversetk12\undersetk21\ightleftharpoons(RR′NH\underset(II)2+···OH−)\oversetk23\undersetk32\ightleftharpoonsRR′N\underset(III)H+H2O, the rate-determining step is the proton-transfer process, (II) \ightleftharpoons (III). The pKb values of the secondary amines ...

The ultrasonic absorptions of Aerosol OT in dodecane solution were measured in the frequency range 5–95 MHz at various temperatures. An excess absorption caused by single relaxation was observed above the second critical micelle concentration. This is attributed to the conformational change in structure of two kinds of Aerosol OT micelles, since the maximum excess absorption per wave length depends on the concentration and temperature. The thermodynamic and kinetic parameters were determined in relation to the reaction.