Reactions of N1-Methyl-4-nitro-2,1,3-benzoselenadiazolium Tetrafluoroborate with Aliphatic and Cyclic Amines in Acetonitrile: Kinetic and Structure-Reactivity Correlations

Self Cite

The kinetics of the reactions of benzylidenecyanoacetates 1a-d (X = H, Me, OMe, and NMe 2 ) with nitroalkyl anions 2a-c have been studied in aqueous solution at 20°C. The second-order rate constants are used to evaluate the electrophilicity parameter E of these series of Michael acceptors 1a-d according to the linear free enthalpy relationship log k (20°C) = s N (E + N). The measured E values were found to cover a domain of reactivity, ranging from −10.07 for the most reactive electrophile 1a (X = H) to −14.04 for the less electrophile 1d (X = NMe 2 ). Mayr's approach was found to correctly predict the rate constants for the reactions of these series of olefins 1a-d with the hydroxide ion in water and 50% water-50% acetonitrile at 20°C. Analysis of the kinetic measurements using the Brönsted relationship shows that β nuc values remain remarkably constant for changes in the nature of the substituent X. A notable finding of this work is perhaps provided by the observed large changes in the electrophilicity parameter E on going from benzylidenecyanoacetates 1 to their analogues benzylidenemalonates 3 ( E ß 9.06-10.48), whereas the replacement of second CO 2 Et group by the CN group in 1 to give benzylidenemalononitriles 4 has little effect on electrophilic reactivity, i.e., E ß 0.65-0.95. AZAIEZ, DHAHRI, AND BOUBAKERThis abnormal pattern in the E values has been attributed to the resonance interaction and salvation effects. On the other hand, the effect of benzylidenecyanoacetate substituents on the electrophilic reactivity was examined quantitatively on the basis of the electrophilicity parameter E, leading to linear correlation of E with Hammett-Brown substituent constants (σ + p ). More importantly, the four electrophiles have comparable log k o values, which are located at a relatively low level, i.e., log k o ࣘ 4-5, in the intrinsic reactivity scale.

Section: Resultssupporting

confidence: 80%

“…In all cases, the agreement between calculated and experimental rate constants is remarkably good because Eq. usually predicts rate constants of polar organic reactions within a factor of 10–100 .…”

Section: Resultsmentioning

confidence: 99%

Reactivity of Nitroalkyl Anions Addition to Substituted Benzylidenecyanoacetates: Electrophilicity Parameters and Free Energy Relationships

Azaiez

Dhahri

Boubaker

2017

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“…It is interesting to note that the slopes close to unity (1.02 and 1.08) obtained in this work indicates that equation (1) is applicable to these reactions 7‐10,15‐19 . According to equations (3) and (4), the electrophilicity parameter E values of −8.46 and −9.52 are thus obtained for benzofurazans 1 and 2 , respectively.…”

Section: Resultssupporting

confidence: 70%

Electrophilic reactivities of 7‐L‐4‐nitrobenzofurazans in σ‐complexation processes: Kinetic studies and structure–reactivity relationships

Ayachi

Raissi

Mahdhaoui

et al. 2020

The second‐order rate constants (k) for reaction of 7‐chloro‐4‐nitrobenzofurazan 1 and 7‐methoxy‐4‐nitrobenzofurazan 2 with a series of nitroalkyl anions and several of para‐substituted phenoxide anions in aqueous solution at 20 °C have been reported. On the basis of the linear novel approach recently designed by Mayr and coworkers, the electrophilicity parameters E at the C‐5 position of the two nitrobenzofurazans 1 and 2 have been quantified and ranked on the comprehensive electrophilicity scale. Mayr's approach was found to correctly predict the rate constants for the addition of phenoxide anions at the C‐5 position of 1 and 2 witting a factor of <2. Analysis of the kinetic measurements using Brønsted's model shows that βnuc values remain remarkably constant for changes in the nature of the substituent and that the σ‐complexation process is associated with high Marcus intrinsic barriers. In addition, satisfactory correlations between the log kexp (kexp values measured in this work for reactions of benzofurazans 1 and 2 with a series of phenoxide anions in aqueous solution at 20 °C) and log kcalcd (kcalcd values calculated from equation 1 using the electrophilicity parameters E of benzofurazans 1 and 2 and the previously published nucleophilicity parameters N and sN of the phenoxide anions) with a slope very close to unity have been obtained and discussed.

“…As can be seen, the two rate constant values predicted deviate by less than a factor 35 from the experimental values. It should be noted that here the agreement between calculated and experimental rate constants is satisfactory, because it is generally accepted that the linear free energy relationship (Equation ) can well exactly predict the rate constants of various polar nucleophilic addition and substitution reactions within a factor of 10–100 …”

Section: Resultssupporting

confidence: 58%

“…For example, Ben Salah and co‐workers have found that the rate constants calculated by Equation for the reactions of the N1‐methyl‐4‐nitro‐2,1,3‐benzoselenadiazolium tetrafluoroborate with secondary amines in acetonitrile solution at 20°C deviate by less than a factor 56 from those measured . Raissi and co‐workers have shown that Equation predicts the rate constants for the S N Ar reactions of the 7‐L‐4‐nitrobenzofurazans (L = Cl and OCH 3 ) with anilines in CH 3 CN solution at 20°C within a factor of 2–65 .…”

Section: Resultsmentioning

confidence: 99%

S_NAr reactions of substituted pyridines with secondary amines in aqueous solution: Kinetic and reactivity indices in density functional theory

Mahdhaoui

Zaier

Dhahri

et al. 2019

A kinetic study is reported for the reactions of 2-methoxy-3-nitropyridine 1a and 2methoxy-5-nitropyridine 1b with three secondary amines 2a-c (morpholine, piperidine, and pyrrolidine) in aqueous solution at 20 • C. The Brønsted-type plots are linear with nuc = 0.52 and 0.55 for pyridines 1a and 1b, respectively, indicating that the reaction proceeds through a S N Ar mechanism in which the first step is the ratedetermining step. Additional theoretical calculations using the DFT/B3LYP method confirm that the C-2 carbon being the most electrophilic center for the both pyridines 1a and 1b. The second-order rate constants have been used to evaluate the electrophilicity parameters E of 1a and 1b according to the linear free energy relationship log k (20 • C) = s N (N + E). The E parameters thus derived are compared with the electrophilic reactivities of a large variety of anisoles. The validity of these E values has been satisfactorily verified by comparison of calculated and experimental second-order rate constants for the reactions of pyridines 1a and 1b with anion of ethyl benzylacetate. K E Y W O R D S density functional theory, electrophilicity parameter (E), equation of Mayr, kinetics, S N Ar, substituted pyridine Int J Chem Kinet. 2019;51:249-257.