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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 24, Number 9
BKCSDE 24(9)
September 20, 2003 

Effect of Nonleaving Group on the Reaction Rate and Mechanism: Aminolyses of 4-Nitrophenyl Acetate, Benzoate and Phenyl Carbonate
Ik-Hwan Um, Hye-Ran Park, Eun-Young Kim
Aminolysis, Structure-reactivity relationship, Rate-determining step, Leaving group
Second-order rate constants have been determined spectrophotometrically for the reaction of phenyl 4-nitrophenyl carbonate with a series of primary amines in H2O containing 20 mol % DMSO at 25.0 oC. The Brønsted-type plot is linear with a βnuc 0.69 ± 0.04, which is slightly smaller than the βnuc values for the reactions of 4-nitrophenyl acetate ( βnuc = 0.82 ± 0.03) and benzoate ( βnuc = 0.76 ± 0.01), indicating that the reaction proceeds through a tetrahedral zwitterionic intermediate T±. The carbonate is more reactive than the corresponding acetate and benzoate. The changing Me (or Ph) to PhO has resulted in a decrease in the βnuc value without changing the reaction mechanism but an increase in the reactivity. The electronic effect of the substituent in the nonleaving group appears to be responsible for the enhanced reactivity of the carbonate compared with the corresponding acetate and benzoate.
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