A SYSTEMATIC STUDY ON THE COMPLEXATION OF QUATERNARY AMMONIUM-SALTS AND NEUTRAL PHENOLS

Complexation of quaternary ammonium salts (Q(+)X(-)) and undissociated , neutral phenols (ArOH) in homogeneous organic solutions was systemat ically investigated to afford a reliable quantitative basis for a new model of anionic potentiometric response to neutral phenols, displayed by organic liquid membranes based on Q(+)X(-). IR, H-1- and C-13-NMR, and UV studies indicated complexation of Q(+)X(-) and ArOH in 1 : 1 s toichiometry in nonpolar organic solvents such as benzene and chlorofo rm. The stability constant (K-s) of the complex was affected by the ac idity and lipophilicity of the ArOH component as well as the size of X - of the Q(+)X(-) component; stronger complexes were formed by ArOH wi th a lower pK(a) and higher log P-oct, as well as by Q(+)X(-) with a s maller ionic radius for X-. These results suggest that the major drivi ng force for complexation is hydrogen bonding interactions between X- and the phenolic OH. The K-s values were found to be parallel with the magnitudes of anionic potentiometric responses by membranes based on Q(+)X(-), indicating that the complexation of ArOH by Q(+)X(-) plays a n important role in the anionic potentiometric responses. The signific ance of proton dissociation from the Q(+)X(-) ArOH complex was also di scussed.