Model of acid-base equilibrium for ion-exchangers considering association of functional group

Abstract

The model of acid-base equilibrium for ion exchanger was proposed according to law moving
mass with consideration of association of functional groups. It was shown that along with dissociation of
acidic functional groups [HA] (dissociation constant KD1) there take place the formation of dimmers
[H2A2] (Kdim) and associates [HA2
-], (Kassoc). The three above mentioned equilibrium constants allow
determination of the concentration of the corresponding species [HA], [H2A2] and [HA2
-], make it
possible to model experimental data, and describe the influence of electron-donating properties of the
substituents at ionogenic groups [–Р(О)(Х)ОН] on the equilibrium. The influence of chemical structure of
ionogenic groups on dissociation and association constants was quantitatively described using σф as factor
electron-donating properties of the substituents on phosphorus by Kabachnik.
The adequacy of the proposed model for description of acid base equilibrium was proved by
good correlation between calculated and experimental data for phosphonic acid ion exchange resins. The
comparison of acid-base equilibrium parameters of the proposed model and of Gregor’s model was
performed. It was shown that pKD1 and pKa obtained by the two models are practically identical.
Correlation between the parameters encountering cooperative interaction, of the two models (nGr, Kassoc)
was also quite good.