Water and hydroxide ion pathways in the σ-complexation of superelectrophilic 2-aryl-4,6-dinitrobenzotriazole 1-oxides in aqueous solution. A kinetic and thermodynamic study

Abstract

As part of our continuing studies of the highly electron-deficient nature of nitrobenzofuroxans, nitrobenzofurazans and related heterocycles, we report here a kinetic and thermodynamic study of σ-complexation for a series of 2-aryl-4,6 -dinitrobenzotriazole 1-oxides (3a-e) over a large pH range in aqueous solution. The reaction series represents a modulation in electrophilic properties of the benzotriazole moiety in formation of the corresponding hydroxy σ-adducts (4a-e). Analysis of the data has allowed dissection of observed rates into forward (k) and reverse (k H ϩ Ϫ1 , k Ϫ2 ) rate constants as well as the obtention of pK a values for H 2 O addition to the benzotriazole moiety. Our results reveal that 3a-e are superelectrophilic compounds with respect to 1,3,5-trinitrobenzene (TNB) as a standard electron-deficient aromatic, but less superelectrophilic compared to 4,6-dinitrobenzofuroxan (DNBF). Some data pertaining to buffer catalysis of the formation and decomposition of the adducts together with solvent deuterium isotope effects for these pathways are also reported. From these results, it is concluded that adduct formation occurs via general base catalyzed water attack: the general bases include notably H 2 O, HCO 3 Ϫ , CO 3 2Ϫ as well as OH Ϫ . This contrasts with the situation for the σ-complexation of DNBF where HCO 3 Ϫ and CO 3 2Ϫ were found to act as nucleophilic catalysts whereas OH Ϫ functioned as a general base catalyst. This contrasting behaviour provides further evidence that the dinitro-activated carbocyclic ring of the benzotriazoles 3a-e ranks somewhat lower in electrophilic/ superelectrophilic properties compared to that in DNBF. Altogether, the results provide a basis for understanding the relationship between the superelectrophilic reactivities, as evidenced by the contrasting kinetic and thermodynamic properties of the systems at hand, and the varied abilities of these substrates to react in pericyclic Diels-Alder reactions.

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

“…Figure also reveals that the benzoselenadiazolium cation 1 displays an electrophilicity approximately 2.5–12.3 orders of magnitude less reactive that the other N‐electrophiles (i.e., di‐ter‐butyl azodicarboxylate 11 ( E = −12.23) , 4‐chlorobenzenediazonium 12 ( E = −6.70) , and 2,4‐dinitrobenzenediazonium tetrafluoroborate 13 ( E = −2.50) ) and 1.53 orders of magnitude more negative than that of 1,3,5‐trinitrobenzene 14 , the reference for the benzenoid electrophiles .…”

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:…”

Theoretical investigation of methoxide ion reaction on the 7-methyl-4,6-dinitrobenzofuroxan

“…Geometric structures and electronic distribution analysis of all compounds resulting from the action of NBF and DNBF with methoxide anion were previously studied [32,33]. Our calculated geometrical values of DNBF are close to NBF experimental structure [34] determined by x-ray diffraction.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] They have also been intensively studied from the point of view of the chemical activity. [14][15][16][17][18][19][20][21][22] In particular, a great deal of interest in recent decades has been caused by the fact that benzofuroxans exhibit a high capacity to undergo σ-complexation or covalent substitution. The action of the methoxide anion on the 4,6-dinitro7-methylbenzofuroxan (DNBF) leads only to the isolation of the anionic form DNBF -.…”