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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 1
BKCSDE 34(1)
January 20, 2013 

Decomposition of Paraoxon and Parathion by Amines, HOO and OH Ions:Reaction Mechanism and Origin of the α-Effect
Ae-Ri Bae, Jieun Lee, Ik-Hwan Um*
Paraoxon, Parathion, Concerted mechanism, Solvent effect, Polarizability effect
The second-order rate constants have been measured spectrophotometrically for the reactions of paraoxon 1 and parathion 2 with a series of alicyclic secondary amines, OH– and HOO– ions in H2O at 25.0 ± 0.1 oC. A linear Brønsted-type plot with βnuc = 0.40 was obtained for the reactions of 1 with amines and OH–. The reaction has been concluded to proceed through a concerted mechanism. HOO– deviates positively from the linear Brønsted-type plot, implying that the α-effect is operative. The magnitude of the α-effect (kHOO−/kOH−) was found to be ca. 55 for the reaction of 1 and 290 for that of parathion 2, indicating that HOO– is highly effective in decomposition of the toxic phosphorus compounds although it is over 4 pKa units less basic than OH–. Among the theories suggested as origins of the α-effect (e.g., TS stabilization through an intramolecular Hbonding interaction, solvent effect, and polarizability effect), polarizability effect appears to be the most important factor for the α-effect in this study, since the polarizable HOO– exhibits a larger α-effect for the reaction of the more polarizable substrate 2.
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