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Author Abu-Omar, M. M. ♦ Hansen, P. J. ♦ Espenson, J. H.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CHEMISTRY ♦ RHENIUM COMPLEXES ♦ NMR SPECTRA ♦ ULTRAVIOLET SPECTRA ♦ VISIBLE SPECTRA ♦ DECOMPOSITION ♦ CHEMICAL REACTION KINETICS ♦ PEROXIDES ♦ HYDROGEN PEROXIDE ♦ PH VALUE
Abstract The peroxides from methylrhenium trioxide (MTO) and hydrogen peroxide, CH{sub 3}ReO{sub 2}({eta}{sup 2}-O{sub 2}), A, and CH{sub 3}Re(O)({eta}{sup 2}-O{sub 2}){sub 2}(H{sub 2}O), B, have been fully characterized in both organic and aqueous media by spectroscopic means (NMR and UV-vis). In aqueous solution, the values of the equilibrium constants for their formation are given. In the presence of hydrogen peroxide the catalyst decomposes to methanol and perrhenate ions with a rate that is dependent on [H{sub 2}O{sub 2}] and [H{sub 3}O{sup +}]. The complex peroxide and pH dependences could be explained by one of two possible pathways: attack of either hydroxide on A or HO{sub 2}{sup -} on MTO. The respective second-order rate constants for these reactions which were deduced from comprehensive kinetic treatments are given. The plot of log k{sub {psi}} versus pH for the decomposition reaction is linear with a unit slope in the pH range 1.77-6.50. The diperoxide B decomposes much more slowly to yield O{sub 2} and CH{sub 3}ReO{sub 3}. This is a minor pathway, however, amounting to <1% of the methanol and perrhenate ions produced from the irreversible deactivation at any given pH. Without peroxide, CH{sub 3}ReO{sub 3} is stable below pH 7, but decomposes in alkaline aqueous solution to yield CH{sub 4} and ReO{sub 4}{sup -}. As a consequence, the decomposition rate rises sharply with [H{sub 2}O{sub 2}], peaking at the concentration at which [A] is a maximum, and then falling to a much smaller value. 29 refs., 10 figs., 2 tabs.
ISSN 00027863
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-05-29
Publisher Place United States
Journal Journal of the American Chemical Society
Volume Number 118
Issue Number 21


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