Kinetic studies of the Hydrolysis of n-Octylamine on the Surface of a Sodium Dodecyl Sulfate Micelle by the Ultrasonic Absorption Method

Article abstract of DOI:10.1021/j150644a035

Ultrasonic relaxation absorption has been observed in aqueous solution of n-octylamine (OA) in the presence of micelles of sodium dodecyl sulfate (SDS).From various experiments changing (i) the concentrations of OA and SDS, (ii) the alkyl-chain length of the detergent and amine, (iii) the pH of the solution, and (iv) the type of detergent, the relaxation absorption has been ascribed to the hydrolysis of OA on the surface of the SDS micelle: C8H17NH3⁺ + OH^- <-> C8H17NH2 + H2O.The forward (k_f) and backward (k_b) rate constants, the apparent equilibrium constant (K), and the volume change (ΔV) for the hydrolysis have been determined to be γ²k_f = 5.5*10⁸ M^-1 s^-1, k_b = 1.2*10⁷ s^-1, K (=γ²k_f/k_b) = 45 M^-1, and ΔV = 26.5 cm³ mol^-1 at 20 deg C, respectively, where γ is the mean ionic activity coefficient.The values of γ²k_f and K were found to be smaller than the corresponding values in the absence of the micelle by a factor of about 1/50.These micellar effects have been interpreted in terms of electrostatic interactions between the micelle and OH^- and OA⁺ ions.