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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 15, Number 6
BKCSDE 15(6)
June 20, 1994 

A Mechanistic Study on Nucleophilic Substitution Reactions of Aryl Substituted Benzenesulfonates with Anionic Nucleophiles
Ik-Hwan Um*, Seok-Joo Lee, Jung-Joo Kim, Dong-Sook Kwon
Second-order rate constants have been measured spectrophotometrically for the nucleophilic substitution reactions of aryl substituted benzenesulfonates (1, X-C6H4SO2-OC6H4-Y) with aryloxides (Z-C6H4O-) and ethoxide (EtO-) in absolute ethanol at 25 ℃. The nucleophilicity of aryloxides increases with increasing electron donating ability of the substituent (Z) on aryloxides, and results in a good Hammett correlation with σ- constant. The reactivity of 1 toward aryloxides and ethoxide shows also significant dependence on the electronic nature of the substituent X and Y. Large positive ρacyl values have been obtained for the reaction of 1 with phenoxide and ethoxide, indicating that the leaving group departure is little advanced at the transition-state of the rate-determining step. This has been further supported from the fact that σ- constant gives extremely poor Hammett correlation, while σ0 does reasonably good correlation for the reaction of 1 with ethoxide. Thus, the present sulfonyl-transfer reaction is proposed to proceed via a ratedetermining attack of nucleophile to the sulfur atom of 1 followed by a fast leaving group departure.
473 - 477
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