Cinétique et thermodynamique de la σ-complexation du 2-(4’-nitrophényl)-4,6-dinitrobenzotriazole1-oxyde en solution aqueuse
Written by sctunisie no commentsRate and equilibrium constants for the σ-complexation of 2-(4'-nitropheny1)-4,6- dinitrobenzatriazole 1-oxide (2a) have been mesured over a large pH range in aqueous solution. The pKa value for the formation of the expected hydroxy σ-complex 4a is equal to 9.00±0.03, pointing out that this species is more stable than all related σ-adducts previously studied in benzene, naphthalene or pyridine series. In contrast 4a is 2 x 105 times less stable than the hydroxy σ-adduct of 4,6-dinitrobenzofuroxan (DNBF). This indicates that the electrophilicity of 2a is remarkable without being as exceptional as that of DNBF. This conclusion is supported by the finding that water addition to 2a is a rather negligible process in the formation of 4a. Also, the susceptibility of 2a to hydroxide ion attack is 50 times lower than that of DNBF. Reasonable mechanisms for the formation of the adduct 4a are discussed on the basis of the observed buffer catalysis and deuterium isotope effects.
T. Boubaker, A.P. Chatrousse, B. Tangour, F. Terrier
Benzotriazoles,σ-adduits, Substitutions Nucloophiles Aromatiques, Cinetique de σ-complexation, Superelectrophiles
Pages 1497-1507
