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Oxidation of thioanisole by peroxomolybdate ions: direct oxygen transfer from tetraperoxomolybdate ion
Author(s) -
Bunton Clifford A.,
Gillitt Nicholas D.
Publication year - 2002
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.442
Subject(s) - chemistry , reaction rate constant , thioanisole , crystallography , absorbance , analytical chemistry (journal) , order (exchange) , oxygen , ion , equilibrium constant , kinetics , catalysis , physics , organic chemistry , chromatography , quantum mechanics , biochemistry , finance , economics
Addition of thioanisole (PhSMe) to Na 2 MoO 4 in dilute hydrogen peroxide at pH 9.4 rapidly quenches the absorbance of the tetraperoxo complex, $\hbox{Mo}(\hbox{O}_{2})_{4}^{2-}$ , which gradually regenerates as the PhSMe is oxidized to the sulfoxide. This direct oxygen transfer is followed by the decreasing absorbance of $\hbox{Mo}(\hbox{O}_{2})_{4}^{2-}$ at 452 nm. In dilute H 2 O 2 the $\hbox{Mo}(\hbox{O}_{2})_{4}^{2-}$ becomes a steady‐state intermediate, and kinetics monitored by 1 H NMR spectroscopy allow estimation of the second‐order rate constant for oxidation of PhSMe by $\hbox{MoO}(\hbox{O}_{2})_{3}^{2-}$ and rate constants for interconversion of $\hbox{MoO}(\hbox{O}_{2})_{3}^{2-}$ and $\hbox{MoO}(\hbox{O}_{2})_{4}^{2-}$ . The steady‐state approximation breaks down at higher [H 2 O 2 ], and with [H 2 O 2 ] = 2 M the $\hbox{MoO}(\hbox{O}_{2})_{3}^{2-}$ and $\hbox{Mo}(\hbox{O}_{2})_{4}^{2-}$ are approximately in equilibrium; based on the rate constants of oxidation of PhSMe by $\hbox{MoO}(\hbox{O}_{2})_{3}^{2-}$ and $\hbox{Mo}(\hbox{O}_{2})_{4}^{2-}$ and the related association equilibrium constant, the observed and predicted rate constants for the overall oxidation of PhSMe are similar. Copyright © 2001 John Wiley & Sons, Ltd.