Effect of Acyl Substituents on the Reaction Mechanism for Aminolyses of 4-Nitrophenyl X-Substituted Benzoates

Abstract

Second-order rate constants (k(N)) have been measured spectrophotometrically for the reaction of 4-nitrophenyl X-substituted benzoates with a series of alicyclic secondary amines in H(2)O containing 20 mol % dimethyl sulfoxide at 25.0 degrees C. The magnitude of the k(N) values increases with increasing the basicity of amines and with increasing the electron-withdrawing ability of the acyl substituent X. The Hammett plots obtained are not linear but show a break or curvature as the acyl substituent X becomes electron withdrawing for all the amines studied, while the Bronsted-type plots are linear with large beta(nuc) values for all the substrates investigated. The nonlinear Hammett plots suggest a change in the rate-determining step upon changing the acyl substituent X, whereas the linear Bronsted-type plots indicate that the rate-determining step does not change upon changing amine basicity. The Yukawa-Tsuno plots obtained are also linear with positive rho(X) and large r values, suggesting that the nonlinear Hammett plots are not due to a change in the rate-determining step upon changing the acyl substituent X, but due to resonance demand of the pi-electron donor substituent on the acyl moiety. The magnitude of the rho(X) and beta(nuc) values increases with increasing the basicity of amines and with increasing the electron-withdrawing ability of the acyl substituent X, respectively, while that of the r values decreases with increasing rho(X) values and amine basicity.

Kinetic Study on Aminolysis of Y-Substituted-Phenyl Picolinates: Effect of H-Bonding Interaction on Reactivity and Transition-State Structure

“…5 In contrast, the corresponding reactions of O-4-nitrophenyl thionobenzoate (2) have been suggested to proceed through a stepwise mechanism with two intermediates (e.g., T ± and T -) since the plots of k obsd vs.…”

“…We have also reported that aminolysis of 4-pyridyl Xsubstituted-benzoates (5) in MeCN proceeds through a stepwise mechanism with one or two intermediates depending on the electronic nature of the substituent X, e.g., T ± and T -when X is a strong electron-withdrawing group (EWG) but T ± only when X is a weak EWG or an electron-donating group (EDG).…”

Kinetic Study on Aminolysis of 4-Nitrophenyl Nicotinate and Isonicotinate: Factors Influencing Reactivity and Reaction Mechanism

“…We have recently reported that aminolysis of 4-nitrophenyl picolinate (6) in H 2 O containing 20 mol % DMSO proceeds through a stepwise mechanism with a cyclic intermediate as modeled by T III on the basis of a linear Brønsted-type plot with β nuc = 0.78. 12 We have shown that 6 is over 35 times more reactive than 2a.…”

On the mechanism of the reaction between aryl acetates and hydroxylamine

“…[1][2][3][4][5][6][7][8][9] Besides describing the structural relationships which lead to the reactivity of carboxylic acid derivatives, the search for nucleophiles able to cleave selectively peptide and ester bonds is still a challenge in many areas of chemistry and biochemistry. [10][11][12] The development of such stable and highly reactive nucleophiles has a wide range of applications in chemical detoxification, e.g., where quantitative phosphate bond cleavage is the target.…”