Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol by bis(hydrogen periodato)argentate(III) complex anion: a kinetic study |
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| Authors: | Hongmei Shi Weijun Kang Shigang Shen Hanwen Sun |
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| Institution: | (1) School of Public Health, Hebei Medical University, Shijiazhuang, 050017, Hebei Province, People’s Republic of China;(2) College of Chemistry and Environmental Science, Hebei University, Baoding, 071002, Hebei Province, People’s Republic of China |
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| Abstract: | Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol (MPPD) by bis(hydrogenperiodato) argentate(III) complex anion, Ag(HIO6)2]5− has been studied in aqueous alkaline medium by use of conventional spectrophotometry. The major oxidation product of MPPD
has been identified as 3-(4-methoxyphenoxy)-2-ketone-1-propanol by mass spectrometry. The reaction shows overall second-order
kinetics, being first-order in both Ag(III)] and MPPD]. The effects of OH−] and periodate concentration on the observed second-order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced:where IO4
−]tot denotes the total concentration of periodate and k
a = (0.19 ± 0.04) M−1 s−1, k
b = (10.5 ± 0.3) M−2 s−1, and K
1 = (5.0 ± 0.8) × 10−4 M at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k
a and k
b have been calculated. A mechanism is proposed, involving two pre-equilibria, leading to formation of a periodato–Ag(III)–MPPD
complex. In the subsequent rate-determining steps, this complex undergoes inner-sphere electron-transfer from the coordinated
MPPD molecule to the metal center by two paths: one path is independent of OH−, while the other is facilitated by a hydroxide ion. |
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![$$ {{k^{\prime} = \left( {k_{\text{a}} + k_{\text{b}} \left {{\text{OH}}^{ - } } \right]} \right)K_{ 1} } \mathord{\left/ {\vphantom {{k^{\prime} = \left( {k_{\text{a}} + k_{\text{b}} \left {{\text{OH}}^{ - } } \right]} \right)K_{ 1} } {\left\{ {{\text{f}}\left( {\left {{\text{OH}}^{ - } } \right]} \right)\left {{\text{IO}}_{ 4}^{ - } } \right]_{\text{tot}} + K_{ 1} } \right\}}}} \right. \kern-\nulldelimiterspace} {\left\{ {{\text{f}}\left( {\left {{\text{OH}}^{ - } } \right]} \right)\left {{\text{IO}}_{ 4}^{ - } } \right]_{\text{tot}}\, +\, K_{ 1} } \right\}}}, $$](/content/q66hg640862g2668/11243_2008_9162_Article_Equa.gif)