Electron transfer. 107. Chromium(VI)-Uranium(IV) reaction. Parallel one- and two-electron paths

Journal Article · Wed Mar 06 04:00:00 EST 1991 · Inorganic Chemistry; (United States)

DOI:https://doi.org/10.1021/ic00005a030· OSTI ID:5900201

Ghosh, M C; Gelerinter, E; Gould, E S ^[1]

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1. Kent State Univ., OH (United States)

Reduction of HCrO{sub 4}{sup {minus}} with U(IV) in solutions buffered by 2-ethyl-2-hydroxybutanoic acid (HLig) and its salt (Lig{sup {minus}}) is rapid and leads to a mixture of bis chelates of Cr(IV), Cr(V), and Cr(III), each derived from the buffering anion. The ratio of products approaches 3:1:1 and is nearly independent of (Lig{sup {minus}}). Kinetic patterns suggest that the complexes U{sup IV} (Lig{sup {minus}}) and U{sup IV}(Lig{sup {minus}}){sub 2} are active reductants but that U{sup IV}(Lig{sup {minus}}){sub 3} is inactive. With U(IV) in excess, Cr(IV) is slowly reduced to Cr(III), a reaction which must involve intervention of U(V). The U(IV)-Cr(IV) reaction appears to proceed through a precursor complex (K{sub assn} = 5 {times} 10{sup 3} M{sup {minus}1}), the pool of which is depleted both by protonation and extraligation. With Cr(VI) in excess, Cr(IV) is slowly lost by comproportionation (Cr{sup IV} + Cr{sup VI} {yields} 2Cr{sup V}), a transformation which has been observed also in Cr(VI)-As(III) and Cr(VI)-Mo{sub 2}{sup V} systems. Cr(III), formed quickly in the initial stage of conversion in quantity equivalent to Cr(V), cannot arise from the Cr(V)-U(IV) or the Cr(IV)-U(IV) reaction, both of which are too slow, but is instead produced by reduction of Cr(IV) with U(V). ESR studies show that rapid reductions of excess HCrO{sub 4}{sup {minus}} with Mo{sub 2}O{sub 4}{sup 2+}, HSO{sub 3}{sup {minus}}, or Sn(II) in the authors buffer system likewise yield, along with major quantities of Cr(IV), minor amounts of Cr(V), thus pointing to competitive 1e{sup {minus}} and 2e{sup {minus}} transactions with these reductants. Reduction by As(III) under the same conditions, however, yields only Cr(IV).

• OSTI ID: 5900201
• Journal Information: Inorganic Chemistry; (United States), Journal Name: Inorganic Chemistry; (United States) Vol. 30:5; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400702 -- Radiochemistry & Nuclear Chemistry-- Properties of Radioactive Materials
ACTINIDE COMPOUNDS
BUFFERS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMATES
CHROMIUM COMPOUNDS
DATA
EXPERIMENTAL DATA
INFORMATION
KINETICS
NUMERICAL DATA
OXYGEN COMPOUNDS
REACTION KINETICS
REDOX REACTIONS
TRANSITION ELEMENT COMPOUNDS
URANIUM COMPOUNDS