Liquid−Liquid Equilibria of 5-Methyl-2-Pyrazinecarboxylic Acid in Systems (Aqueous Solution with Increased Ionic Strength) + (Solvent with Trioctylamine)

Abstract

Liquid−liquid equilibrium data of 5-methyl-2-pyrazinecarboxylic acid (MPCA) in two-phase systems with acidic aqueous solution containing Na2SO4 and/or NaCl and organic solvent (trioctylamine (TOA) + xylene) are presented. Data from systems containing Na2SO4 were successfully correlated using an equilibrium model. Modeling of systems with chlorides needs more data. MPCA and inorganic acids are extracted simultaneously via two mechanisms. The first is competitive extraction of MPCA and inorganic acids for free TOA. This results in the formation of binary (MPCA + TOA) and (inorganic acid + TOA) complexes. The second mechanism is coextraction of acids resulting in ternary complexes (MPCA + inorganic acid + TOA). Competitive extraction dominates in the presence of NaCl. This suppressed the extraction of MPCA because its affinity to TOA is much lower compared to HCl. Coextraction dominates in the presence of Na2SO4. In this case, extraction of MPCA is comparable or even better than in systems without inorganic species. A solvent with (H2SO4 + TOA) complexes which are de facto ionic liquids provides better extraction of MPCA from aqueous solutions.