N. G. SELLERS, P. M. P. ELLER, AND J. A. CARUSO
3618
Theoredcd Models for Acid-Base Equilibrium Data in Nonaqueous Solvents by Neal G. Sellers, Peter M. P. Eller, and Joseph A. Caruso" Dapartment of Chemistry, University of Cincinnati, Cincinnati, Ohio 46991
(Received April 10,1978)
Interpretations of conductance, potentiometric, and spectrophotometric behavior of weak acids and bases in nonaqueous solvents have been made in terms of complex equilibria. A theoretical model was used which assuined possible existence of some or all of the following species: HA, H+, A-, AHA-, HAB+, (HA)Z, A(HA)t-, fl(HA)2+, (HA)3, A(HA)Z-, and H(HA)a+. The effects of the various equilibrium combina2,ionson the shape of --log A vs. -log C, E vs. -log C,and -log [A-] us, -log C plots are illustrated. Explanations in terms of appropriate equilibrium systems are given for slopes obtained from theoretical conductance, potentiometric, and photometric plots. Theoretical data from these models are compared with experimental conductance, potentiometric,and photometric data from the literature. Introduction The purpose of this study was to develop models based on a generalized multiple equilibrium scheme Within the past 20 years many studies of acid-basc which would yield qualitative and semiquantitative equilibria in nonaqueous solvents have been underinformation as to the types and extent of the equilibria taken. These studies have involved both amphioccurring. Thus, the bounds are defined within which protic and aprotic solvents and generally have utilized experimental data for acids and bases in nonaqueous c o n d ~ c t a n c e ,po?entiometric,10~12 ~~~ or spectrophotomedia must lie for a particular equilibrium scheme to metrio2s1Lmethods of measurement and have been done be valid. It must be emphasized that the following in both bufftmd arid unbuffered solutions. Kolthoff models are intended for purc solvents only. A study has demonstrated that trace acidic or basic impurities presently is being conducted in order to determine the can have a marked effect on acid-base equilibria in dieffect of various impurities on the equilibrium processes. polar aprolk solvents.12 Hence, acid-base equilibrium The need for several experimental techniques to prostudies a t low concentrations (
