Bulletin of the Korean chemical society | |
Kinetics and Mechanism of Azidolysis of Y-Substituted Phenyl Benzoates | |
Eun-Hee Kim1  Hyun-Joo Hana1  Ik-Hwan Um1  | |
关键词: Acyl-transfer reaction; Azidolysis; Br©ªnsted-type plot; Hammett plot; Yukawa-Tsuno plot; | |
DOI : | |
学科分类:化学(综合) | |
来源: Korean Chemical Society | |
【 摘 要 】
Second-order rate constants (kN) have been measured spectrophotometrically for reactions of Y-substituted phenyl benzoates (1a-h) with azide ion (N3-) in 80 mol % H2O/20 mol % DMSO at 25.0 �? 0.1 oC. The Br┆nstedtype plot for the azidolysis exhibits a downward curvature, i.e., the slope (�?1g) changes from ?0.97 to ?0.20 as the basicity of the leaving group decreases. The pKao (defined as the pKa at the center of the Br┆nsted curvature) is 4.8, which is practically identical to the pKa of the conjugate acid of N3- ion (4.73). Hammett plots correlated with �?o and �?- constants exhibit highly scattered points for the azidolysis. On the contrary, the corresponding Yukawa-Tsuno plot results in an excellent linear correlation with �? = 2.45 and r = 0.40, indicating that the leaving group departs in the rate-determining step. The curved Br┆nsted-type plot has been interpreted as a change in the rate-determining step in a stepwise mechanism. The microscopic rate constants (k1 and k2/k-1 ratio) have been calculated for the azidolysis and found to be consistent with the proposed mechanism.
【 授权许可】
Unknown
【 预 览 】
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