Journal of Organic Chemistry p. 2666 - 2672 (1980)
Update date:2022-08-11
Topics:
Terrier, Francois
Chatrousse, Alain-Pierre
Millot, Francois
In methanolic solution,methoxide ions attack both the 5- and 7-carbons of 4-nitrobenzofurazan (5) and 4-nitrobenzofuroxan (8) to give the Meisenheimer-type complexes 6, 9 and 7, 10.The kinetics of the interactions have been studied by the stopped-flow method.The formation of the 5-methoxyl adducts 6 and 9 is found to always precede that of the thermodynamically more stable 7-methoxyl isomers 7 and 10.The results indicate that the para-like 4-nitro group is more efficient than the furazan and the furoxan rings in delocalizing the negative charge in 7 and 10.The kinetic and thermodynamic parameters Δ H0, Δ S0, Δ H(excit.), and Δ S(excit.) or the various reactions have been determined.It appears that only a large positive entropy change, Δ S0 (about +80 J/mol*K), is responsible for both the formation and the greater stability of the 7-methoxyl complexes 7 and 10 as compared to that of their 5-methoxyl analogues.Stabilization of 7 and 10 by association of the 4-nitro group with the potassium counterion is suggested.
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