The association constants of Na+ with dibenzo[3n]crown-n in THF/water using ISE

The Na+ association constants, K11 and β12, of 1/1 and 1/2 stoichiometry of macrocycles of (1,2)dibenzo[15]crown-5, (1,3)dibenzo[18]crown-6, (1,4)dibenzo[21]crown-7, (2,3)dibenzo[21]crown-7, (2,4)dibenzo[24]-crown-8 and dicyclohexano[24]crown-8 were determined in THF/water, (50/50), mixtures. We used a Methrom Na+ ISE for the potentiometric measurements and applied the 1/(βnm[Ao+])n+m−1=(1−nPc)(1−mPc)/Pc equation where the Pc=P/[1+(m−1)P] and P is the mole fraction of the complexed cation, [An+Lm] for association constants with linear best fit. Results were in well agreement with the macrocyclic size and cation radii relationships. Measurements showed the role of aromatic groups of macrocyclics in THF/water (50/50) which allowed the macrocyclic molecules more selectively bind Na+ compared to the associations those obtained in water.