Experimental evidence, stability, and the most probable structure of protonated p-tert-butylcalix[4]arenetetrakis(N,N-dimethylacetamide)

Abstract

AbstractFrom extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H 3 O + (aq) + 1·Na + (nb) [FORMULA]1·H 3 O + (nb) + Na + (aq) taking place in the two-phase water-nitrobenzene system (1 = p-tert-butylcalix[4]arenetetrakis(N,N-dimethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (H 3 O + , 1·Na + ) = −0.1 ± 0.1. Further, the stability constant of the 1·H 3 O + complex in water-saturated nitrobenzene was calculated for a temperature of 25 °C as log β nb (1·H 3 O + ) = 10.9 ± 0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1·H 3 O + cationic complex species was derived. In this complex, the hydroxonium ion H 3 O + is bound partly to one phenoxy oxygen atom and partly to two carbonyl oxygens of 1 by strong hydrogen bonds and obviously by other electrostatic interactions.Graphical Abstract[IMAGE]