A study of proton transfer by 2,2′-bipyridine from water to nitrobenzene using chronopotentiometry with cyclic linear current-scanning and cyclic voltammetry

Abstract

2,2′-Bipyridine can extract protons from the aqueous phase to nitrobenzene at pH 1.5–5.5. The extraction process has been investigated by chrono-potentiometry with cyclic linear current-scanning and cyclic voltammetry. The complex ion is formed in the aqueous phase by the reaction between hydrogen ion and 2,2′-bipyridine that has diffused from the organic phase. The transfer process is diffusion-controlled. The transfer species is a 1 : 1 proton–bipyridine complex. The formal transfer potential, Δ^w_oϕ^°_tr, and the apparent Gibbs energy, ΔG^{°, w→o}_tr, for the protonated bipyridine transfer at the water–nitrobenzene interface is found to be –0.005 V and –0.48 kJ mol^–1, respectively. The distribution constant of free bipyridine between the two phases was calculated as log K= 1.3 ± 0.1. The diffusion coefficients of the free and protonated bipyridine in the organic and aqueous phase, D_L and D_HL+, are (6.4 ± 0.3)× 10^–6 cm²s^–1 and (7.2 ± 0.3)× 10^–6 cm² s^–1, respectively.