Kinetics and Mechanism of the Aminolysis of Aryl Phenyl Chlorothiophosphates with Anilines in Acetonitrile

초록

The kinetics and mechanism of the nucleophilic substitution reactions of aryl phenyl 55℃. The obtained cross-interaction constant is negative, pXY=-0.20(Y=p-MeO-H) and 0.26(Y=H-p-CN), suggesting that the reaction proceeds by an SN2 mechanism. The Hammett plots of logk2 vs δY show a break at δY= 0 to a large dependence of logk2 on the phenoxide group suggesting changes in the TS structrue to more associative type for the electron withdrawing Y substituents (δY > 0) with tighter bond fromation. The rates are much slower than the corresponding reactions of aryl phenyl Chlorothiophosphates, (C6H5O)P(+O)(CI)OC6H4Y;2, due to lower electrophilicity of P in P=S relative P=O because of electronegativity differsnces, favouring O over S. The primary kinetics isotope effects (kH/kD=1.18-1.27) with deuter deuterated aniline nucleophiles were observed, in contrast the secondary kinetics effects (kH/kD = 0.61-0.87) for 2. △H± (7.0-13.0 kcal mol-1) and △S± (-32 to -54 cal mol-1 k-1)mvalues are obtained. The selectivity parameters, px (=-3.18 to -4.01), βx(=1.34-1.41) and two distinct pY(0.25-0.49 for δY < 0 and 0.79-1.07 for δY > 0) values of 1 are similar to 2 but the magnitudes of pXY are much smaller than that with 2 ( pXY = -1.31), suggesting similar mechanism of 2, a concerted process with a late, product-like transition atate in which bond marking and leaving group departure are extensive.