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Protonation of Benzo-18-crown-6: Extraction and DFT Study

  • Petr Toman , Emanuel Makrlík , Petr Vaňura and Vaclav Kašička
Published/Copyright: December 9, 2010

Abstract

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H3O+(aq) + 1·Na+(nb)⇌1·H3O+(nb) + Na+(aq) taking place in the two-phase water-nitrobenzene system (1 = benzo-18-crown-6, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex(H3O+, 1·Na+)=-0.8±0.1. Further, the stability constant of the 1·H3O+ complex in water-saturated nitrobenzene was calculated for a temperature of 25°C as log βnb(1·H3O+)=6.3±0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1·H3O+ cationic complex species was derived. In this complex, the hydroxonium ion H3O+ is bound by three strong linear hydrogen bonds to one (Ar–O–CH2) ethereal oxygen and two (CH2–O–CH2) ethereal oxygen atoms of the parent crown ligand 1. The interaction energy was found to be -401.4kJ/mol, confirming the formation of the considered complex 1·H3O+.


* Correspondence address: University of West Bohemia, Faculty of Applied Sciences, Husova 11, 306 14 Pilsen, Tschechische Republik,

Published Online: 2010-12-9
Published in Print: 2011-2-1

© by Oldenbourg Wissenschaftsverlag, Pilsen, Germany

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