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
- 주제(키워드) Aryl benzenesulfonates , Alkaline hydrolysis , Sulfonyl-group transfer , Yukawa-Tsuno plot , Concerted mechanism
- 발행기관 WILEY-V C H VERLAG GMBH
- 발행년도 2015
- 총서유형 Journal
- URI http://www.dcollection.net/handler/ewha/000000117836
- 본문언어 영어
- Published As http://dx.doi.org/10.1002/bkcs.10297
초록/요약
Second-order rate constants (k(OH)-) 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 k(OH)- with the k(N3)- values reported previously for the corresponding reactions with N-3- has revealed that OH- is only 10(3)-fold more reactive than N-3-, although the former is 11 pK(3) units more basic than the latter. The Yukawa-Tsuno plot for the reactions of 1a-1f results in an excellent linear correlation with rho(X) = 2.09 and r = 0.41. The Bronsted-type plot for the reactions of 2a-2g is linear with beta(lg) = -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 rho(Y) = 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 rho(X) and beta(lg) values for the reactions with OH- and N-3- ions suggests that the reactions with hydroxide ion proceed through a tighter transition-state structure than those with azide ion.
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