Nucleophilicities of Para-Substituted Phenoxide Ions in Water and Correlation Analysis

Abstract

Second-order rate constants for the reactions of 2-aryl-4,6-dinitrobenzotriazole 1-oxides 1a-d with some 4-X-substituted phenoxide ions 2a-d (X = OCH 3 , H, Cl, and CN) have been measured in aqueous solution at 20 • C. The pK a values for the σ -complexation processes of a series of benzotriazole 1a-d measured in water have been used to determine their electrophilicity parameters E according to the correlation E = -3.20 -0.662 pK a (F. Terrier, S. Lakhdar, T. Boubaker, and R. Goumont, J Org Chem, 2005, 70, 6242-6253). For these reactions, plots of log k versus the electrophilicity parameters E of the benzotriazoles 1a-d were linear, allowing to derive the nucleophilicity parameters N and s for phenoxide ions as defined by the Mayr equation log k 1 (20 • C) = s (E + N) (H. Mayr, M. Patz. Angew Chem, Int Ed Engl 1994, 33, 938-957). The N values are found to cover a range of nucleophilicity from 6.85 to 10.22, going from 4-cyanophenoxide 2d for the least reactive ion to 4-methoxyphenoxide 2a for the most reactive nucleophile. Good linear correlations were found between the nucleophilicity parameters N of phenoxide ions 2a-d and the pK a values of their conjugate acids (N = -3.05 + 1.25 pK a ) and the σ p constants of the substituents X (N = 9.21 -2.51σ p ). C 2014 Wiley Periodicals, Inc. Int J Chem Kinet 46: 711-717, 2014

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

“…As the electrophilicity parameters E for the nitrobenzofurazans 1 and 2 have been evaluated in this work, it was therefore interesting to use these values to predict the rate constants describing the nucleophilic addition of other nucleophiles to the C‐4 carbon atom of these nitrobenzofurazans 1 and 2 . In fact, using the parameters N and s N for a series of para‐X‐substituted phenoxide anions 10a‐d recently determined in aqueous solution by Gabsi and coworkers 40 and the E parameters of the electrophiles 1 and 2 determined in this study, second‐order rate constants ( k calcd ) have been calculated by equation (1). 7 These values are summarized in the Table 3, together with those experimental values ( k exp ) measured in the present work under the same conditions.…”

The ambident electrophilic behavior of 5‐nitro‐3‐X‐thiophenes in σ‐complexation processes

“…As the nucleophilicity parameters N and s for the series of parasubstituted phenoxide anions 3a–d have been recently determined in aqueous solution, it was therefore interesting to use these values to calculate the electrophilicity parameters E describing the nucleophilic addition of phenoxide ion to the C‐4 and C‐2 carbon atoms of thiophenes 1 and 2 . In fact, using the data given in Table , plots of (log k 1 )/ s versus N have been drawn for each of the phenoxide anions 3a–d , as illustrated in Figure , showing the four straight lines obtained for thiophenes 1 and 2 .…”

Kinetic Studies on SNAr Reactions of Substituted Benzofurazan Derivatives: Quantification of the Electrophilic Reactivities and Effect of Amine Nature on Reaction Mechanism

“…In a series of papers , we have shown that the rate constants k (mol −1 L s −1 ) associated with the σ‐complexation reactions can be classified under the rubric of the original linear‐free energy relationship (LFER) proposed in 1994 by Mayr and co‐workers (Eq. ) , in which E is an electrophilicity parameter, s N is the nucleophile‐specific slope parameter, and N is a parameter characteristic of the given nucleophile in the given solvent and independent of the electrophile:…”

“…On the basis of this equation, the electrophilicity parameters E for several neutral electron‐deficient electrophiles, namely nitrobenzofuroxans , nitrotetrazolopyridines , nitrobenzofurazans , nitropyridine , and nitrobenzotriazoles have been quantified and ranked on the comprehensive electrophilicity scale defined for cationic electrophiles by Mayr and co‐workers . We noted that Mayr's approach has also been used to describe the reactivity of S N Ar substrates such as 7‐chloro‐4,6‐dinitrobenzofuroxan and ‐benzofurazan , 1‐X‐2,4‐dinitrobenzenes (X = F, Cl, Br and I) , and 2‐methoxy‐3‐X‐5‐nitrothiophenes (X = SO 2 CH 3 , CO 2 CH 3 , CONH 2 , and H) .…”