Structure-reactivity correlations in the reaction of 2,4-dinitrophenyl X-substituted benzoates with alicyclic secondary amines

Abstract

Apparent second-order rate constants (kapp) have been measured spectrophotometrically for the reaction of 2,4-dinitrophenyl X-substituted benzoates with a series of alicyclic secondary amines in H2O containing 20 mol% DMSO at 25°C. The microconstants involved in the reaction (k-1/k2, k1, and k1k2/k-1) have also been calculated. The magnitude of kapp, k1, and k1k2/k-1 values increases with increasing amine basicity and with increasing acid strengthening ability of the acyl substituent X. The k-1/k2 value decreases from ca. 6.5 to 0.3 with increasing the amine basicity, but remains almost constant upon changing the acyl substituent X for a given amine, indicating that the rate-determining step is governed by the basicity of amine but not by the electronic nature of the acyl substituent X. The Brønsted-type plots for kapp show a break at pKa = 9.1, supporting the assumption that a change in the rate-determining step occurs from rate-limiting breakdown to formation of the addition intermediate as amine basicity increases. The corresponding Brønsted-type plots for k-1/k2, k1, and k1k2/k-1 are linear but their β values are different. σ+ constants show better correlation with log kapp, log k1 and log k1k2/k-1 for the reaction with low basic amines (pKa < 9.1), while σ constants exhibit better correlation for the reaction with highly basic amines (pKa > 9.1). The magnitude of ρ1 is identical to that of ρapp and ρeq for a given amine.Key words: aminolysis, Brønsted-type plot, structure-reactivity correlations, rate-determining step.

Aminolysis of Y-Substituted Phenyl 2-Thiophenecarboxylates and 2-Furoates: Effect of Modification of Nonleaving Group from 2-Furoyl to 2-Thiophenecarbonyl on Reactivity and Mechanism

“…In fact, we have shown that the electronic nature of the substituent X does not influence the k 2 /k -1 ratio in reactions of 2,4-dinitrophenyl X-substituted benzoates with a series of secondary amines. 12 The same result has been obtained in this study. As shown in Figure 3, i.e., the k 2 /k -1 ratio is almost identical for the reactions of 5a-h and 6a-h, although 2-furoic acid (pK a = 3.16) is a stronger acid than 2-thiophenecarboxylic acid (pK a = 3.53).…”

“…6,7 However, we have proposed that the k 2 /k -1 ratio is independent of the electronic nature of the substituent X in the nonleaving group. 5,12 This is because both the amine and leaving aryloxide leave with the bonding electrons from the zwitterionic intermediate T ± . Accordingly, an electron donating substituent X would increase both k 2 and k -1 while an electron withdrawing X would decrease both k 2 and k -1 .…”

Aminolysis of 2,4‐Dinitrophenyl X‐Substituted Benzoates and Y‐Substituted Phenyl Benzoates in MeCN: Effect of the Reaction Medium on Rate and Mechanism

“… [a] Data in the parenthesis are rate constants for the corresponding reactions performed in H 2 O containing 20 mol % DMSO. Data taken from reference 5a. …”

“…[b] The p K a data in MeCN taken from reference 18. [c] Data taken from reference 5a. [d] Data taken from reference 9b.…”

Kinetics and Mechanism for the Reaction of 4-Nitrophenyl 2-Thiophenecarboxylate with Secondary Alicyclic Amines

“…The magnitude of βnuc value has also been suggested to represent the degree of the effective charge developed on the N atom at the transition state (TS) of aminolysis reactions. [12][13][14] Therefore, one might consider the positive charge developed on the N atom at the TS is slightly more significant for the reaction of 1a than that of 1b or 1c, based on their βnuc values.…”