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), Vol. 21:7
- Country of Publication:
- United States
- Language:
- English
Similar Records
Kinetic and mechanistic studies of the reactions of selected aliphatic radicals with metal complexes and the decomposition of organoperoxy cobalt complexes. [C(CH/sub 3/)/sub 2/OH and CH(CH/sub 3/)OC/sub 2/H/sub 5/ radicals]
Kinetics and mechanisms of the reactions of aliphatic free radicals with organocobaloximes and fluoropentaamminecobalt(III) ion, and of iron(III) with methylrhodoxime. [C(CH/sub 3/)/sub 2/OH and C(CH/sub 3/)OC/sub 2/H/sub 5/ radicals]
Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHROMIUM COMPLEXES
DECOMPOSITION
COBALT COMPLEXES
CHEMICAL REACTIONS
DEUTERIUM
ISOTOPE EFFECTS
HYDROXYL RADICALS
ABSORPTION SPECTRA
ALKANES
AMINES
AQUEOUS SOLUTIONS
CHEMICAL REACTION KINETICS
DEUTERIUM COMPOUNDS
ELECTRON TRANSFER
EXPERIMENTAL DATA
HEAVY WATER
HYDRATES
PERCHLORATES
PH VALUE
REACTION INTERMEDIATES
REDUCTION
STRUCTURAL CHEMICAL ANALYSIS
WATER
CHLORINE COMPOUNDS
COMPLEXES
DATA
DISPERSIONS
HALOGEN COMPOUNDS
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INFORMATION
ISOTOPES
KINETICS
LIGHT NUCLEI
MIXTURES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
RADICALS
REACTION KINETICS
SOLUTIONS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
400302* - Organic Chemistry- Isotope Effects- (-1987)
400301 - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)