Extraction of Some Univalent Salts into 1,2-Dichloroethane and Nitrobenzene: Analysis of Overall Extraction Equilibrium Based on Elucidating Ion-pair Formation and Evaluation of Standard Potentials for Ion Transfers at the Interfaces between Their Diluents and Water

Abstract

Sodium permanganate, sodium picrate (NaPic), Bu₄NPic, Me₄NPic, and Et₄NPic were extracted at an ionic strength of 2 × 10⁻⁵ to 0.08 mol dm⁻³ and 25°C from water (w)-phases into the organic (o)-ones, 1,2-dichloroethane (DCE) and nitrobenzene (NB). Thereby, apparent distribution constants (K_D,±) of the anions (A⁻) or the cations (M⁺) and ion-pair formation ones (K_MA^org) of the univalent salts (MA) in the o-phases were determined at 25°C, where K_D,± = ([A⁻]_o[M⁺]_o/[A⁻][M⁺])^1/2 = (K_D,AK_D,M)^1/2 and K_MA^org = [MA]_o/[M⁺]_o[A⁻]_o. Also, the K_ex and K_D,MA values with A⁻ = Pic⁻, MnO₄⁻ were estimated from the relations K_ex (= [MA]_o/[M⁺][A⁻]) = K_MA^org(K_D,±)² and = K_MAK_D,MA, respectively. Standard potentials (Δφ_tr⁰) for ion transfers at the w/DCE and w/NB interfaces were evaluated from the log K_D,A or log K_D,M values by assuming the relations K_D,Pic = K_D,Et4N and = K_D,Me4N, respectively. The thus-obtained Δφ_tr⁰ values, especially for the w/DCE system, were in good agreement with the values based on the extra-thermodynamic assumption for Ph₄As⁺ and BPh₄⁻ transfers at the interfaces. In the present extraction systems, the ion-pair formation of MA in the w- and o-phases was less effective in the determination of their distribution constants into the two o-phases.