Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution; temperature dependence.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied at 303.2, 308.2, 313.2, and 318.2K, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc at each temperature above. The Gibbs free energy change of the solubilizates from aqueous bulk to their liquid solubilizate phase was evaluated from dependence of their aqueous solubility on alkyl chain length of the solubilizates, which leads to the DeltaG(CH0)(2) values (-3.60 to -3.38 kJ mol(-1)), the energy change per CH2 group of the alkyl chain with no strong temperature dependence. The first stepwise solubilization constant (K1) was evaluated from the slope for the change of solubilizate concentration vs. Mega-10 concentration. The Gibbs free energy change (DeltaG(0,s)) for the solubilization decreased linearly with the carbon number of alkyl chain of the solubilizates, and the DeltaG(CH0)(2)(s) values (-2.71 to -2.54 kJ mol(-1)) obtained from the linearity showed a slight increase with temperature. The DeltaG(CH0)(2) values are less than the DeltaG(CH0)(2)(s) values, where the latter values clearly indicate that the location of alkyl chain is a hydrophobic micellar core. The fact is also supported by the absorption spectrum of the solubilized molecules. Temperature dependence of DeltaG(0,s) indicated that the solubilization is entropy-driven for the solubilizates with shorter alkyl chains, while it becomes enthalpy-driven for those with longer alkyl chains.

Hydrolysis of ionized deoxycholic acid in the aqueous phase and rate analysis for transfer of neutralized deoxycholic acid into the benzene phase across the benzene/water interface.

Sodium deoxycholate in water dissociates into sodium cation and deoxycholate anion in the aqueous phase, and then, the latter anions partially hydrolyze to form deionized deoxycholic acids. The acids move into the benzene phase, when liquid benzene is placed upon the aqueous phase, and finally the partition equilibrium is reached. The above processes were traced by pH change in the aqueous phase by a pH meter or the change in [OH-] with time, from which the rate for transfer of neutralized acid to the organic phase was analyzed. From the trace, the rate constants for hydrolysis of acid anion ( kf), neutralization of acid ( kb), transfer of neutralized acid from the aqueous phase to the organic phase ( kin*), and its back-transfer from the organic phase to the aqueous phase ( kut*) were evaluated; kf = 2.18 x 10 (-4) mol (-1) dm (3) min (-1), kb = 1.24 x 10 (5) mol (-1) dm (3) min (-1), kin* = 4.06 x 10 (-1) min (-1) cm (-2), and kout*) = 8.00 x 10 (-2) min (-1) cm (-2). The above values are supported by the partition constant of deoxycholic acid between the benzene phase and the aqueous phase.

Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically at 303.2 K. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc. The Gibbs free energy change of the solubilizates from the aqueous bulk to the liquid solubilizate phase was evaluated from the dependence of their aqueous solubility on the alkyl chain length of the solubilizates, which leads to -3.46 kJ mol-1 for DeltaG(0)(CH), the energy change per CH2 group of the alkyl chain. The first stepwise solubilization constant (K(overline)1 ) was evaluated from the slope of the change of solubilizate concentration versus Mega-10 concentration. The Gibbs free energy change (DeltaG(0,s)) for the solubilization decreased linearly with the carbon number of the alkyl chain of the solubilizates, from which DeltaG(0,s)(CH2) as evaluated to be -2.71 kJ mol-1. The similar values above clearly indicate that the location of the alkyl chain is a hydrophobic micellar core, which is also supported by the absorption spectrum of the solubilized molecules.

A kinetic and thermodynamic study on hydrolysis of sodium laurate in aqueous phase accompanied by transfer into oil phases containing different organic additives (I).

The kinetic and thermodynamic behavior at the interface between an aqueous solution of sodium laurate (NaLA) and various oil phases comprised primarily of benzene (Bz) and/or different organic compounds including amphiphiles has been investigated in regard to the hydrolysis of NaLA accelerated at the interface, transfer of lauric acid (LA) into oil phase and reverse transfer of Bz into aqueous phase in addition to interface tension. The contact of aqueous NaLA solution with the oil phase was found to accompany the mass transfer of LA and simultaneously promote the hydrolysis of NaLA in water phase. Analysis of the change of OH- ion concentration ([OH-]) over time allowed us to treat the events as a first order reaction. From the rate constant data the activation parameters such as the activation enthalpy and entropy, both of which control the transfer of LA molecules, were determined. The parameters were found to depend greatly on varied situations of the oil phase, being clearly able to explain the physicochemical behavior of the interface. Comparing the cases where the oil phase is one of the respective single systems such as Bz, dodecane (C12) and dodecylbenzene (C12Bz), C12Bz resulted in the lowest rate constant. The transfer (or hydrolysis) rate was measured for the amphiphile-added oil systems as a function of amphiphile concentration. When 0.206 M C16OH-Bz came in contact with aqueous phase, emulsion formation at the interface layer was brought about with approximately zero activation enthalpy, leading to facile or spontaneous transfer of LA. In addition, UV absorbance representing the transfer of Bz from the oil phase to the aqueous phase also demonstrated the effects of added amphiphiles on the action of the interface.