Phase behavior of benzyltributylphosphonium salts in aromatic hydrocarbonsor aqueous solutions

The solubility of benzyltributylphosphonium salt (BTBPX: X = Cl, Br, or I) in aromatic hydrocarbons was examined as a function of the temperature. The solubility curve had specific features, which were characterized by critic al values corresponding to the Krafft point and critical micelle concentrat ion. A slight difference in the oil structure exerted a significant effect on the solubility behavior. The Krafft boundary as well as a liquid-liquid immiscibility gap, on the other hand, featured the solubility behavior of B TBPX in an aqueous solution. The shape of the gap was assumed to be a close d loop and the region of the gap was sharply dependent on the concentration of the added metal halide (NIX). The phase behavior of the three- or four- component systems, composed of BTBPX, benzene, water, and NIX, has been exa mined in detail. According to their constituent, composition, and temperatu re, the system afforded a single- to four-phase state form. There were at l east three kinds of liquid phases: a BTBPX-rich phase (M), an aqueous solut ion phase (W), and an oil solution phase (O). When these three liquid phase s coexist, the system affords an O-M-W three-liquid-phase equilibrium state . The three-liquid phase may be converted to O-M or M-W two-liquid-phase, d epending on the temperature and MX concentration in the W phase. In the pre sence of excess MX (S), BTBPCl gave an O-M-W-S four-phase state, while BTBP Br or BTBPI never formed a four-phase state. The phase behavior of the four -component systems is discussed based on phase diagrams of fewer component systems.