Extraction of calcium from water into nitrobenzene using strontium dicarbollylcobaltate in the presence of 18-crown-6

From extraction experiments and g-activity measurements, the extraction constant corresponding to the equilibrium Ca2+(aq) + SrL2+(nb) « CaL2+(nb) + Sr2+(aq) taking place in the two-phase water-nitrobenzene system (L = 18-crown-6, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex(Ca2+, SrL2+) = -1. 9±0.1. Furthermore, the stability constant of the calcium - 18-crown-6 complex in nitrobenzene saturated with water was calculated for the temperature of 25°C: log bnb (CaL2+) = 10.1±0.1.