Mechanism of oxidation of alkyl and superoxo complexes of chromium (III) by aquamanganese(III) ions
The reaction between aqueous manganese(III) ions, Mn(H{sub 2}O){sub 6}{sup 3+}, and (H{sub 2}O){sub 5}CrOO{sup 2+} has a 1:1 stoichiometry and generates Cr(H{sub 2}O){sub 6}{sup 3+} and O{sub 2} as products. The mixed second-order rate constant exhibits an [H{sup +}] dependence that identifies the hexaaquamanganese ion as the reactive form at 0.5 {le} [H{sup +}] {le} 3.0 mol L{sup -1}, k{sub H} = 350 {+-} 10 (mol L{sup -1}){sup -1} s{sup -1}. The reactivity of (H{sub 2}O)5MnOH{sup 2+} is negligible under these conditions, most likely because the much lower reduction potential of this hydrolytic form results in unfavorable thermodynamics for the overall reaction. Mn(H{sub 2}O){sub 6}{sup 3+} also oxidizes a benzylchromium ion, (H{sub 2}O)5CrCH{sub 2}Ph{sup 2+}, with a rate constant k = 273 {+-} 13 (mol L{sup -1}){sup -1} s{sup -1} in 3.0 mol L{sup -1} HClO{sub 4}. The reaction has a 2:1 [Mn(H{sub 2}O){sub 6}{sup 3+}]/[(H{sub 2}O){sub 5}CrCH{sub 2}Ph{sup 2+}] stoichiometry and generates benzyl alcohol as the sole organic product. The data are consistent with oxidative homolysis which generates benzyl radicals followed by rapid oxidation of the radicals with the second equivalent of Mn(H{sub 2}O){sub 6}{sup 3+}. The unexpected similarity between the rate constants for the Mn(H{sub 2}O){sub 6}{sup 3+} oxidation of (H{sub 2}O){sub 5}CrOO{sup 2+} and (H{sub 2}O){sub 5}CrCH{sub 2}Ph{sup 2+} is discussed.
- Research Organization:
- Ames Laboratory (AMES), Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC02-07CH11358
- OSTI ID:
- 1031637
- Report Number(s):
- IS-J 7551
- Journal Information:
- Journal of Coordination Chemistry, Journal Name: Journal of Coordination Chemistry Journal Issue: 14-16 Vol. 63; ISSN JCCMBQ; ISSN 0095-8972
- Country of Publication:
- United States
- Language:
- English
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