ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Combined kinetic, and theoretical approaches for the study of the S_EAr reactions of 2-(2′,4′,6′-trinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide with 5-R-substituted indoles in acetonitrile

Ons Amamou, Amel Hedhli, Takwa Slama, Sahbi Ayachi, and Taoufik Boubaker

Laboratoire de Chimie Hétérocyclique, Produits Naturels et Réactivité (LR11SE39), Faculté des Sciences de Monastir, Université de Monastir, Monastir, Tunisia

E-mail: boubaker_taoufik@yahoo.fr

Received: 19 January 2024  Accepted: 21 March 2024

Abstract:

We present a kinetic and theoretical study of electrophilic aromatic substitution (S_EAr) involving 2-(2′,4′,6′-trinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide 1 with a series of 5-R-substituted indoles 2a-e (R = CN, Cl, H, Me and NH₂) in acetonitrile at 20 °C. Single electron transfer (SET) mechanism was proposed and confirmed by the agreement between the rate constants (k) and the oxidation potentials (E_p^ox) of these series of indoles. Using Mayr's equation, the electrophilicity parameter (E) of 1 at C-7 position is derived and compared with the same parameter estimated using empirical equation E versus. pK_a. Density Functional Theory (DFT) calculations were performed to confirm the suggested reaction mechanisms and elucidate the origin of the electrophilic reactivity of 1. Notably, a linear correlation (R² = 0.9957) between the experimental nucleophilicity (N) and the theoretical model of nucleophilicity (ω⁻¹) determined in this work of various 5-R-substituted indoles has been obtained and discussed.

Graphical abstract

Mayr and Parr's approaches were combined with the correlation N vs ω⁻¹ established in the present work, to evaluate the empirical electrophilicity parameter (E) of 2-(2′,4′,6′-trinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide and the unknown nucleophile specific parameters (N and s_N) of four new 5-R-substituted indoles (R = NO₂, F, H and N(CH₃)₂) in acetonitrile.

Keywords: Kinetics; Benzotriazoles; Equation of Mayr; Electrophilicity; Nucleophilicity; Single electron transfer mecanism; DFT analysis

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-024-03440-3

Chemical Papers 78 (8) 4919–4933 (2024)