Oxidation of aqueous europium(II) and chromium(II) ions by perchlorate and oxidation of europium(II) ions by hydronium ions: Catalysis by methyltrioxorhenium(VII)

INOR 369

James H. Espenson and Yang Cai. Department of Chemistry, Iowa State University, 25 Spedding Hall, Ames, IA 50011
The reactions cited in the title do not occur in practice, even over long time periods, despite their being spontaneous. The oxidations with perchlorate have ΔE° = 1.61 V (ΔG° = –155 kJ / mol of ClO4 ) and those with H3O+ have ΔE° = 0.42 V (ΔG° = –40 kJ mol-1). The oxidations with perchlorate ions are catalyzed by MeReO3 (MTO). MTO also catalyzes the oxidation of Eu2+ by H3O+, whereas Cr2+, with the same value of E°, does not evolve H2 in the presence of MTO. The reaction stoichiometries are cleanly 8 M2+ + 8 H+ + ClO4 = 8 M3+ + Cl + 4 H2O and 2 Eu2+ + 2 H3O+ = 2 Eu3+ + H2. The kinetics and mechanisms will be reported.