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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 29, Number 12
BKCSDE 29(12)
December 20, 2008 

A Mechanistic Study on Alkaline Hydrolysis of Y-Substituted Phenyl Benzenesulfonates
Li Ra Im, Youn Min Park, Ik Hwan Um*
Alkaline hydrolysis, Rate-determining step, Concerted mechanism, Transition state, Yukawa-Tsuno equation
Second-order rate constants (kOH-) have been measured spectrophotometrically for reactions of Y-substituted phenyl benzenesulfonates (1a-h) with OH? in H2O containing 20 mol % DMSO at 25.0 ± 0.1 oC. The Brønstedtype plot is linear with βlg = ?0.55 including the points for the reactions of 2,4-dinitrophenyl benzenesulfonate (1a) and 4-chloro-2-nitrophenyl benzenesulfonate (1c), indicating that the ortho-nitro group on the leaving aryloxide does not exert steric hindrance in the current reactions. The Hammett plot correlated with σo constants exhibits highly scattered points, while the Hammett correlation with σ? constants results in a slightly better correlation but still many points deviate from the linearity. In contrast, the Yukawa-Tsuno plot shows an excellent linear correlation with r = 0.52, implying that leaving-group departure occurs at the RDS either in a stepwise mechanism or in a concerted pathway. However, the stepwise mechanism in which the leaving group departs in the RDS is excluded since the incoming OH? is much more basic and a poorer nucleofuge than the leaving aryloxide. Thus, the alkaline hydrolysis of 1a-h has been concluded to proceed through a concerted mechanism.
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