Kinetic Study on Alkaline Hydrolysis of Y-substituted Phenyl X-substituted Benzenesulfonates: Effects of Changing Nucleophile from Azide to Hydroxide Ion on Reactivity and Transition-State Structure.

Second-order rate constants () for alkaline hydrolysis of 2,4-dinitrophenyl X-substituted benzenesulfonates ( 1a-1f) and Y-substituted phenyl 4-nitrobezenesulfonates ( 2a-2g) have been measured spectrophotometrically. Comparison of with the values reported previously for the corresponding reactions with has revealed that OH is only 103-fold more reactive than , although the former is 11 p Ka units more basic than the latter. The Yukawa-Tsuno plot for the reactions of 1a-1f results in an excellent linear correlation with ρX = 2.09 and r = 0.41. The Brønsted-type plot for the reactions of 2a-2g is linear with βlg = −0.51, which is typical for reactions reported to proceed through a concerted mechanism. The Yukawa-Tsuno plot for the reactions of 2a-2g exhibits excellent linearity with ρY = 1.85 and r = 0.25, indicating that a partial negative charge develops on the O atom of the leaving group in the transition state. Thus, the alkaline hydrolysis of 1a-1f and 2a-2g has been concluded to proceed through a concerted mechanism. Comparison of the ρX and βlg values for the reactions with ions suggests that the reactions with hydroxide ion proceed through a tighter transition-state structure than those with azide ion. [ABSTRACT FROM AUTHOR]