Novel method for the chemical generation of aliphatic radicals and its application to the kinetics of reduction of cobalt(III)-amine complexes by 2-hydroxy-2-propyl radicals
Homolytic cleavage of the chromium-carbon bond in the complex (H/sub 2/O)/sub 5/CrC(CH/sub 3/)/sub 2/OH/sup 2 +/ provides a ready source of the carbon-centered radical C(CH/sub 3/)/sub 2/OH in strongly acidic solutions, pH 0 to 3. The kinetics of reaction of the radical with another substrate present in solution can be studied in competition with the recombination reaction between radical and Cr/sup 2 +/. The method was applied to a study of the reduction of several cobalt(III) complexes, with the following pH-independent rate constants at 25.0/sup 0/C: Co(NH/sub 3/)/sub 6//sup 3 +/, 4.1 x 10/sup 5/ M/sup -1/ s/sup -1/; Co(ND/sub 3/)/sub 6//sup 3 +/, 3.0 x 10/sup 5/; Co(en)/sub 3//sup 3 +/, 1.7 x 10/sup 5/; Co(tn)/sub 3//sup 3 +/, 1.9 x 10/sup 6/; Co(chxn)/sub 3//sup 3 +/, < 1 x 10/sup 4/. The mechanism of Co(NH/sub 3/)/sub 6//sup 3 +/ reduction over the entire pH range 0 to 14 has been reformulated as consisting of three pathways: (1) outer-sphere electron transfer from C(CH/sub 3/)/sub 2/OH, dominant at pH 0 to 3; (2) outer-sphere electron transfer from C(CH/sub 3/)/sub 2/O/sup -/, dominant at pH > 10; (3) reversible formation of a covalent intermediate, (NH/sub 3/)/sub 5/CoNH/sub 2/C(CH/sub 3/)/sub 2/OH/sup 2 +/, whose subsequent decomposition is the prevalent reaction at intermediate pH, pH 5 to 9. The rate constants for the first of these reactions correlate well with lambda/sub max/ and E/sup 0/ values of the Co(III) complexes and with the rate constants for the corresponding reduction by Cr(bpy)/sub 3//sup 2 +/, save for Co(chxn)/sub 3//sup 3 +/ whose low reactivity with the free radical is attributed to its conformational inflexibility. Several Cr(III) complexes-Cr(NH/sub 3/)/sub 6//sup 3 +/, Cr(urea)/sub 6//sup 3 +/, and (H/sub 2/O)/sub 5/CrCl/sup 2 +/-failed to react with C(CH/sub 3/)/sub 2/OH. 4 figures, 6 tables.
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6645409
- Journal Information:
- Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 21:7; ISSN INOCA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ABSORPTION SPECTRA
ALKANES
AMINES
AQUEOUS SOLUTIONS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHLORINE COMPOUNDS
CHROMIUM COMPLEXES
COBALT COMPLEXES
COMPLEXES
DATA
DECOMPOSITION
DEUTERIUM
DEUTERIUM COMPOUNDS
DISPERSIONS
ELECTRON TRANSFER
EXPERIMENTAL DATA
HALOGEN COMPOUNDS
HEAVY WATER
HYDRATES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXYL RADICALS
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
MIXTURES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PERCHLORATES
PH VALUE
RADICALS
REACTION INTERMEDIATES
REACTION KINETICS
REDUCTION
SOLUTIONS
SPECTRA
STABLE ISOTOPES
STRUCTURAL CHEMICAL ANALYSIS
TRANSITION ELEMENT COMPLEXES
WATER