Thermodynamics of dissociation and micellization of sodium, calcium, aluminum, and tin stearates in mixed organic solvents

Abstract

Sodium, calcium, aluminum, and tin stearates behave as weak electrolytes in dilute solutions (60% benzene + 40% methanol, vol/vol) below the critical micelle concentration, and conductance data can be explained on the basis of Ostwald's formula and the Debye-Hückel theory of weak electrolytes. Dissociation constants and thermodynamic parameters for dissociation and micellization of these soaps were also evaluated. Micellization was spontaneous and predominant over the dissociation process. JAOCS 74, 793-796 (1997).Specific and equivalent conductivities of sodium and potassium soaps in alcohols, toluene, and pyridine have been determined by Bhatnagar and Prasad (1). Patrick et al.(2) pointed out that sodium oleate in alcohols behaves as a simple electrolyte. Several workers (3,4) have investigated soap solutions that bridge the transition from aqueous to nonaqueous solutions.Critical micelle concentrations (CMC) of aqueous solutions of magnesium soaps were determined by Varma and Kumar (5). Varma and Dayal (6) studied the conductance behavior of aqueous solutions of barium, strontium, and nickel soaps.Mehrotra and Upadhyaya (7) studied the thermodynamics of dissociation and micellization of praseodymium and neodymium linoleates in mixed organic solvents to determine physicochemical properties and structure.In this work, we focused on conductance and micellar behavior of sodium, calcium, aluminum, and tin (stannic) stearate soaps in a mixture of 60% benzene and 40% methanol (vol/vol) at different temperatures. EXPERIMENTAL PROCEDURESSodium hydroxide (NaOH), calcium sulfate dihydrate (CaSO 4 ·2H 2 O), aluminum sulfate-18-hydrate [Al 2 (SO 4 ) 3 ·18H 2 O], tin (IV) chloride (SnCl 4 ), and stearic acid (C 17 H 35 COOH) were supplied by Merck (Darmstadt, Germany). The melting range of the stearic acid was 68-70°C, and its acid number was 196.Sodium stearate was obtained from the reaction of NaOH with stearic acid. Ca 2+ , Al 3+ , and Sn 4+ stearates were prepared by direct metathesis of Na + stearate with the stoichiometrically required amounts of CaSO 4 ·2H 2 O, Al 2 (SO 4 ) 3 ·18H 2 O, and SnCl 4 in a water-alcohol medium (1:1, vol/vol). The precipitated soaps were washed with water and acetone to remove excess metal ion and unreacted stearic acid.Soap solutions were prepared by dissolving a measured amount of soap in a mixture of 60% benzene and 40% methanol (vol/vol) and were kept for 2 h in a thermostatted water bath at the desired temperature.Conductance of the soap solutions was measured with an Orion digital conductivity meter, Model 126 (Orion Research Inc., Boston, MA), and a dipping-type conductivity cell (cell constant 1.01) with platinized electrodes. The reproducibility of the measurements was ±0.1%. RESULTS AND DISCUSSIONSpecific conductance K of Na + , Ca 2+ , Al 3+ , and Sn 4+ stearate soap solutions in 60% benzene and 40% methanol (vol/vol) increases with increases in soap concentration and temperature. Plots of specific conductance K vs. soap concentration C (Fig. 1) are characterized by the intersec...

Effect of palm kernel oil extraction method on the electrical conductance of Nigerian traditional soaps in alcohols

“…As shown in Figure 5, the concentration conductance decreased with an increase in concentration; this decrease may be due to the combined effects of ionic atmosphere, solvation of ions, and a decrease of mobility and ionization with the formation of micelles. Similar observations have been reported recently by Topallar and colleagues (4,5). The concentration conductances of the pale-orange oil soaps were much higher than those for the black oil soaps, again suggesting the possibility that the pale-orange oil was purer than the black oil.…”

Synthesis of Hollow Co Structures with Netlike Framework

“…Based on the shape evolution of the hollow Co structures shown in Figure , the possible formation mechanism can be described as follows. The cobalt stearate precursor was rapidly formed at the early stage, which had a melting point of 73 °C and thus might be present as liquid crystal, forming micelles in the polar polyol. − The micelle acted as the structure-directing agent in the formation of the hollow Co spheres. Simultaneously, this precursor also acted as Co 2+ reservoir to equilibrate the concentration of Co 2+ species between in cobalt stearate and in the solution.…”