Unexplored metallic cation effect in the acidity constants of p-t-butylthiacalix[4]arene, p-t-butylcalix[4]arene and p-t-butylcalix[6]arene in aqueous-organic media

Abstract

The influence of the metallic cation of the base (Li+, Na+ or K+) was determined on the acid–base constants of p-t-butylthiacalix[4]arene (TC4), p-t-butylcalix[4]arene (CA4) and p-t-butylcalix[6]arene (CA6) in ethanol/water in an large interval of pH values by potentiometry and spectrophotometry. The pKa values determined by both methods correlate very well and these are characteristic for each macrocycle with influence of the cation of the base without a straight evidence of an effect by the size of the metallic cation. In the case of TC4, pKa1 and pKa2 were lower to Li+ and Na+ than with K+. For CA4, an effect of K+ on the pKa2 with respect to Li+ was observed. A very different behaviour was observed for CA6 with Li+ and K+ showing a lower pKa2 and a higher pKa3 than with Na+. These effects were interpreted on the basis of the interaction/complexation of each cation with each macrocycle.