BINARY PHASE-DIAGRAMS OF LEAD(II) N-ALKANOATES AND N-ALKANOIC ACIDS

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 (1:1, 2:1, 3:2, etc.) generally melt incongruently. Besides these peritectic points, a lyotropic mesomorphism is also frequently found. The thallium(I) alkanoates and some acid + salt phase diagrams have been investigated recently, showing formation of only a 1:1 molecular complex, which melts incongruently, and the appearance of lyotropism. on replacing thallium(I) by lead(II), 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.