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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 7
BKCSDE 34(7)
July 20, 2013 

 
Title
Kinetics and Reaction Mechanism for Alkaline Hydrolysis of Y-Substituted-Phenyl Diphenylphosphinates
Author
Hyo-Jeong Hong, Jieun Lee, Ae Ri Bae, Ik-Hwan Um*
Keywords
Brønsted-type plot, Hammett plot, Yukawa-Tsuno plot, Rate-determining step, Concerted mechanism
Abstract
The second-order rate constants (kOH−) for the reactions of Y-substituted-phenyl diphenylphosphinates (4a-4i) with OH– in H2O at 25.0 ± 0.1 oC have been measured spectrophotometrically. Comparison of kOH− with kEtO− (the second-order rate constants for the corresponding reactions with EtO– in ethanol) has revealed that EtO– is less reactive than OH– although the former is ca. 3.4 pKa units more basic than the latter, indicating that the reactivity of these nucleophiles is not governed by their basicity alone. The Brønsted-type plot for the reactions of 4a-4i with OH– is linear with βlg = –0.36. The Hammett plot correlated with σ– constants results in a slightly better correlation than that correlated with σo constants but exhibits many scattered points. In contrast, the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation with ρ = 0.95 and r = 0.55. The r value of 0.55 implies that a negative charge develops partially on the O atom of the leaving group. Thus, the reactions of 4a-4i with OH– have been concluded to proceed through a concerted mechanism.
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