Kinetic studies of the reactions of O,O-diphenyl Z-S-aryl phosphorothioates with X-benzylamines have been carried out in dimethyl sulfoxide at 55.0 $^\circ}C$. The Hammett (log $k_2$ vs $\sigma}_X$) and Bronsted [log $k_2$ vs $pK_a(X)$] plots for substituent X variations in the nucleophiles are biphasic concave downwards with a maximum point at X = H, and the unusual positive $\rho}_X$ and negative $\beta}_X$ values are obtained for the strongly basic benzylamines. The sign of the cross-interaction constant ($\rho}_XZ}$) is negative for both the strongly and weakly basic nucleophiles. Greater magnitude of $\rho}_XZ}$ value is observed with the weakly basic nucleophiles ($\rho}_XZ}$ = -2.35) compared to with the strongly basic nucleophiles ($\rho}_XZ}$ = -0.03). The deuterium kinetic isotope effects ($k_H/k_D$) involving deuterated benzylamines [$XC_6H_4CH_2ND_2$] are primary normal ($k_H/k_D$ > 1). The proposed mechanism is a concerted $S_N2$ involving a frontside nucleophilic attack with a hydrogen bonded, four-center-type transition state for both the strongly and weakly basic nucleophiles. The unusual positive $\rho}_X$ and negative $\beta}_X$ values with the strongly basic benzylamines are rationalized by through-space interaction between the $\pi}$-clouds of the electron-rich phenyl ring of benzylamine and the phenyl ring of the leaving group thiophenoxide.
O,O-二苯基 Z-S-芳基
硫代磷酸酯与 X-
苄胺的反应动力学研究已在
二甲基亚砜中于 55.0
$^\circ}C$ 下进行。哈米特 (log
$k_2$ vs
$\sigma}_X$) 和 Bronsted [log
$k_2$ vs
$pK_a (X)$] 亲核试剂中取代基 X 变化的图是双相凹向下的,最大点位于 X = H,并且异常的正值
$\rho}_X$ 和负值
$\beta}_X$ 值是针对强碱性
苄胺获得的。对于强碱性和弱碱性亲核试剂,交叉相互作用常数 (
$\rho}_XZ}$) 的符号均为负。使用弱碱性亲核试剂观察到更大的
$\rho}_XZ}$ 值 (
$\rho}_XZ}$ = -2.35)与强碱性亲核试剂相比 (
$\rho}_XZ}$ = -0.03)。涉及
氘化
苄胺 [
$XC_6H_4CH_2ND_2$] 的
氘动力学同位素效应 (
$k_H/k_D$) 是初级正态 (
$k_H/k_D$ > 1).所提出的机制是一种协调的
$S_N2$,涉及强碱性和弱碱性亲核试剂的氢键四中心型过渡态的正面亲核攻击。强碱性
苄胺的异常正
$\rho}_X$ 和负
$\beta}_X$ 值通过
$\pi}$-
苄胺的富电子苯环和离去基团
噻吩氧基的苯环的云。