Behavior of some alkali soap systems in organic solvents

Abstract

1. 1. The behavior of sodium oleate, sodium stearate and sodium palmitate toward 40 different organic solvents has been examined. It is found that the soaps do not dissolve in most of the solvents at room temperature, but swell on heating and give clear mobile solutions near the boiling point of the solvent. On cooling these solutions, any one of the following phenomena takes place, depending upon the nature of the soapsolvent system: (1) the soap remains in solution, (2) the soap crystallizes out, (3) a pseudo-gel is formed, or (4) a true gel is obtained. 2. 2. It is observed, in general, that the amount of the gel-like material obtained, that is, the gelating capacity of the soap-solvent system, increases roughly with the boiling point of the solvent. 3. 3. The behavior of the soap-solvent systems giving rise to true gels has been examined with special reference to the degree of supersaturation. It is observed that, if the soap content is low, crystallization occurs when the hot soap-solvent system is. cooled. With an increase in the concentration of the soap, a pseudo-gel is obtained at first, and a true gel is formed only when an optimum concentration of the soap is reached. Further, the transition from the crystalline state to the weak precarious pseudo-gels, and subsequently to the typical stable gels, is effected by very gentle gradations in the concentrations of the soap in the system. 4. 4. The temperatures of crystallization and of the formation of pseudogels and true gels have been measured in the case of the three soaps in 16 different solvents. The zones of concentrations in which the soap exists in the three different states have also been determined.