The Relationship between Melting Points of Metal Soaps with Odd and Even Carbon Numbers and their Critical Solution Temperatures in Benzene

Abstract

In order to investigate the relationship between melting points and solubility behaviors of metal soaps, copper and zinc soaps of saturated straight-chain fatty acids containing both odd and even carbon atoms were prepared, and their melting points and critical solution temperatures in benzene were measured.
In general, metal soaps of the saturated straight-chain fatty acids containing even carbon atoms gave higher melting points than those containing the next odd carbon atoms, similiarly to the phenomenon in fatty acids. The solubilities of copper and zinc soaps in benzene sharply increased at a certain temperature (the critical solution temperature), which was determined by the relation between log S and 1/T. The critical solution temperatures of metal soaps containing even carbon atoms were higher than those of metal soaps containing the next carbon atoms. From these results, the zigzag relationship between the melting point and the critical solution temperature was obtained. These show an upward trend for metal soaps containing even carbon atoms, and a downward trend for those containing odd carbon atoms.