Thermodynamics of Hydrogen-Isotope-Exchange Reactions. I. Electrochemistry in Dimethylformamide

The paper reports our results for the direct experimental determination of the equilibrium constants for the hydrogen-isotope-exchange reaction, D2(g)+2HCl(DMF)=H2(g)+2DCl(DMF), where DMF is the solvent N,N-dimethylformamide. The reaction was studied in electrochemical double cells without liquid junction of the type, (Pt)D2(g) | DCl(DMF) | TlCl(s) | Tl(Hg) | TlCl(s) | HCl(DMF) | H2(g)(Pt).The experimentally determined values of E0(296.6oK) for this cell are Eion0=7.64± 0.38 mV and Eneut0=8.12± 0.54 mV, where Eion0 refers to strong electrolyte standard states for HCl(DMF) and DCl(DMF), and Eneut0 refers to undissociated solute standard states for HCl(DMF) and DCl(DMF). The corresponding experimental values of the equilibrium constants are Kion=1.82± 0.05 and Kneut=1.89± 0.08 (296.6oK). The experimental values of the equilibrium constants are compared with values for K calculated from statistical thermodynamic theory for model reactions.