KCS

The kinetics and mechanism of the pyridinolysis of p-chlorophenyl aryl chlorophosphates (1) have been carried out in MeCN at 5^oC. Lee and coworkers have reported experimentally its (1) aminolysis  (Lee  et al ; Int. J. Chem. Kinet., 2002, 34, 632-637). All the results (r_X, r_Y, b_X, r_XY, kinetic isotope effects and activation parameters) are consistent with a concerted nucleophilic substitution mechanism. The second-order rate constant for substituents at substrate, Y = H,  p-CH₃, p-CH₃O were observed for this reaction. The rates are found faster for the pyridinolysis than its aminolysis . b_X values are smaller in this work (1.14~1.17) than .the aminolysis (1.43-1.49) indicating less degree of bond formation in TS during pyridinolysis. r_X (-5.72 ~ -5.80) supports +ve charge development in reaction center alike aminolysis, r_X (-4.04 ~ -4.24). Relatively low ∆H¹ (2.5−4.7 Kcal mol^-1) and large negative ∆S¹ values (-49~ -54 cal mol^-1K^-1) are within the typical range of S_N2 reaction. Our interest is comparative mechanistic investigation changing nucleophile from primary to tertiary amine.