Binary phase diagrams of lead(II) n-alkanoates and n-alkanoic acids

Abstract

During the last decades there has been a renewed interest in the study of salts with organic anion and /or cation, not only as pure substances but also their mixtures with any kind of solvents. Special attention will be given in this report to the mixtures of organic salts with organic acids. It is well known that the association of alkali alkanoates (@@soaps") and alkanoic acids into a crystalline molecular complexes ("acid soaps") of a given stoichiometry (l:l, 2:1, 3:2, etc.) generally melt incongruently. Besides these peritectic points, a lyotropic mesomorphism is also frequently found. The thallium(1) alkanoates and some acid + salt phase diagrams have been investigated recently, showing formation of only a 1:l molecular complex, which melts incongruently, and the appearance of lyotropism. On replacing thallium(1) by lead(I1) , the binary phase diagram shows completely different features. No molecular association between the acid and the salt is found in the solid state. The complete phase diagram resembles those of the surfactants in water. A Krafft-like point is found, in which the solubility of the salt increases dramatically pointing to the formation of micellar aggregates.The presence of thermotropic mesomorphism corresponds to lyotropism in that region of the phase diagram.

Oleate salt formation and mesomorphic behavior in the propranolol/oleic acid binary system

“…Incongruent melting processes are commonly identified in fatty acid/ fatty acid salt systems, suggesting that the equimolar complex POA was propranolol oleate. 14…”

A study of amorphous molecular dispersions of indomethacin and its sodium salt

“…The interaction between a fatty acid and its salt to form complexes (so‐called “acid soaps”) has been reported in the literature,23 and there are other observations that many other salt/acid pairs can exist in the crystalline state. Ketoprofen sodium, for example, was found to form a mixed crystal with ketoprofen acid at a 2:1 salt:acid molar ratio when the crystals of the salt and acid were triturated in the presence of moisture 24.…”

Ionic Liquid Crystals

“…Single crystals of lead(II) octanoate, lead(II) nonanoate, and lead(II) decanoate have been obtained by a sol−gel technique . The binary phase diagram lead(II) decanoate/decanoic acid has been investigated by Adeosun and Akanni, and binary phase diagrams of this type were further explored by Cheda and co-workers. , The influence of the chain length on the thermal behavior of lead(II) alkanoates has been studied by Adeosun and Sime 380 and reinvestigated by Bazuin and co-workers . The compounds up to lead(II) dodecanoate show a mesophase behavior similar to that of lead(II) decanoate, whereas lead(II) tetradecanoate and higher homologues show only a highly ordered phase but no smectic A phase.…”