Dual Substituent Effects on Pyridinolysis of Bis(aryl) Chlorothiophosphates in Acetonitrile
作者:Hasi Rani Barai、Hai Whang Lee
DOI:10.5012/bkcs.2014.35.6.1754
日期:2014.6.20
The nucleophilic substitution reactions of bis(Y-aryl) chlorothiophosphates (1) with X-pyridines are investigated kinetically in acetonitrile at $35.0^\circ}C$. The free energy relationships with both X and Y are biphasic concave upwards with a break point at X = 3-Ph and Y = H, respectively. The sign of cross-interaction constants (CICs; $\rho}_XY}$) is positive with all X and Y. Proposed mechanism is a stepwise process with a rate-limiting leaving group departure from the intermediate with all X and Y. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorothiophosphates (2). In the case of Y = electron-withdrawing groups, the cross-interaction between Y and Y, due to additional substituent Y, is significant enough to change the sign of $\rho}_XY}$ from negative with 2 to positive with 1, indicative of the change of mechanism from a rate-limiting bond formation to bond breaking.
研究了双(Y-芳基)氯硫代磷酸酯 (1) 与 X-吡啶在乙腈中于 $35.0^\circ}C$ 发生的亲核取代反应的动力学过程。自由能与 X 和 Y 的关系是双相凹陷向上的,断点分别在 X = 3-Ph 和 Y = H 处。交叉作用常数(CICs;$\rho}_XY}$)的符号在所有 X 和 Y 条件下都是正的。在 Y = 失电子基团的情况下,由于额外的取代基 Y,Y 和 Y 之间的交叉作用非常显著,足以改变 $\rho}_XY}$ 的符号,从 2 的负数变为 1 的正数,表明机理从限速成键变为断键。