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Second-order rate constants (k N ) have been measured for nucleophilic substitution reactions of S-4-nitrophenyl thiobenzoate with a series of alicyclic secondary amines in H 2 O containing 20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot exhibits a downward curvature, i.e., β nuc decreases from 0.94 to 0.34 as the amine basicity increases. The reactions in the aqueous DMSO have also been suggested to proceed through a zwitterionic tetrahedral intermediate (T ± ) with change in the RDS on the basis of the curved Bronsted-type plot. The reactions in the aqueous DMSO exhibit larger k N values than those in the aqueous EtOH. The macroscopic rate constants (k N ) for the reactions in the two solvent systems have been dissected into the microscopic rate constants (k 1 and k 2 /k -1 ratio) to investigate effect of medium on reactivity in the microscopic level. It has been found that the k 2/ k -1 ratios are similar for the reactions in the two solvent systems, while k 1 values are larger for the reactions in 20 mol % DMSO than for those in 44 wt % EtOH, indicating that the larger k 1 is mainly responsible for the larger k N . It has been suggested that the transition state is more stabilized in 20 mol % DMSO through mutual polarizability interaction than in 44 wt % EtOH through H-bonding interaction.

bulletin of the korean chemical society

A Kinetic Study on Aminolysis of S-4-Nitrophenyl Thiobenzoate in H<sub>2</sub>O Containing 20 mol % DMSO and 44 wt % EtOH: Effect of Medium on Reactivity and Mechanism

A Kinetic Study on Aminolysis of S-4-Nitrophenyl Thiobenzoate in H2O Containing 20 mol % DMSO and 44 wt % EtOH: Effect of Medium on Reactivity and Mechanism

A Kinetic Study on Aminolysis of S-4-Nitrophenyl Thiobenzoate in H₂O Containing 20 mol % DMSO and 44 wt % EtOH: Effect of Medium on Reactivity and Mechanism