Phase Equilibrium in Diantipyrylmethane–Organic Acid–Hydrogen Chloride–Water Systems

Abstract

Results are presented from studying the mutual solubility of the components in diantipyrylmethane–organic acid (pyrocatechol, salicylic, benzoic)–hydrogen chloride–water systems. It is shown that the size of the phase separation region is affected by the solubility, strength (Ka) of the organic acid, and temperature. In the system with pyrocatechol, the region of separation expands in the range of 1.95 to 9.10 wt % HCl. A subsequent increase in the concentration of acid narrows the region of phase separation, and it is negligible at 24.25 wt % HCl. In systems with salicylic and benzoic acids, the region of phase separation exists at HCl concentrations of 3.0 to 4.9 wt % and expands as the temperature rises. Phase separation is not observed at HCl concentrations of 20.0 and 24.0 wt %. Based on the constants of acidity, pyrocatechol is a weaker acid than salicylic or benzoic, so separation in the first case disappears at a higher concentration of hydrochloric acid. Analysis of the state diagrams allows the effect the concentration of HCl has on the size of the region of phase separation to be established along with the quantitative ratio of phases in the systems. It also makes optimization of the temperature–concentration parameters of extraction possible.