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Second-order rate constants (k OH -) have been measured spectrophotometrically for reactions of Y-substituted phenyl benzenesulfonates (1a-h) with OH - in H 2 O containing 20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot is linear with β 1g = -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 σ o 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.

A Mechanistic Study on Alkaline Hydrolysis of Y-Substituted Phenyl Benzenesulfonates