Complexes between disubstituted benzo-15-crown-5 ligands and sodium or potassium bromides

Stability constants have been determined with ion selective electrodes for complexes between sodium or potassium bromide in methanol with each of four crown ethers, benzo-15-crown-5 (Ia), dibromobenzo-15-crown-5 (Ib), dimethoxybenzo-15-crown-5 (Ic) and di-n-butoxybenzo-15-crown-5 (Id). Those for (Ib) were significantly lower than the others. The stability constants for complexes between sodium bromide and (Ia) and (Ib) in dimethylformamide (DMF) were found to be about one fifth of the corresponding values in methanol. The conductivity method was used to measure the ion pairing in methanol of sodium bromide alone and in the presence of (Ia), (Ib), or (Ic). Ion pairing is increased on complexation, the association constants being 3.3 mol^–1 dm³ for Na⁺ Br^– and 20–23 mol^–1 dm³ for Na(Ia–c)⁺ Br^–. The syntheses of compounds (Ic) and (Id) are described.