An excess concentration of base quinine (Q) reacts with a sulphonphthalein diacidic dye XH2, (bromocresol green, BCGH2, or bromophenol blue, BPBH2) in dichloromethane solution to form an ion associate (X2−(QH+)2) of stoichiometry 1:2 (dye:amine). Benzethonium chloride (ClB) reacts with the 1:2 ion associate to form an ion associate (QH+,X2−,B+) and quinine hydrochloride ClQH+. This substitution reaction is a chemical equilibrium with formation constants of 1.50 ± 0.67, 1.61 ± 0.54, 1.07 ± 0.29, 1.04 ± 0.20, and 0.84 ± 0.26 for BCG and 1.86 ± 0.59, 1.47 ± 0.23, 1.40 ± 0.65, 1.13 ± 0.37, and 1.11 ± 0.27 for BPB at 283.16, 288.16, 293.16, 298.16, and 303.16 K respectively. The thermodynamic parameters determined by van't Hoff's equation are ΔH0 = −21.766 ± 7.482 kJ mol−1, ΔS0 = −73 ± 51 J mol−1 K−1, and ΔG0 = −1.134 ± 0.972 kJ mol−1for BCG and ΔH0 = −18.678 ± 7.482 kJ mol−1, ΔS0 = −61 ± 26 J mol−1 K−1, ΔG0 = −0.916 ± 0.401 kJ mol−1 for BPB (ΔG0 at 293.16 K; and ΔH0 and ΔS0 determined in the range 283–303 K). Key words: bromocresol green – quinine–benzethonium, ion associate mixture, bromophenol blue – quinine–benzethonium, equilibrium constants, thermodynamic parameters.
Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters