N-Demethylation of N,N-Dimethylanilines by the Benzotriazole N-Oxyl Radical: Evidence for a Two-Step Electron Transfer−Proton Transfer Mechanism

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• 作者：Enrico Baciocchi ; Massimo Bietti ; Osvaldo Lanzalunga ; Andrea Lapi ; Daniele Raponi
• 刊名：Journal of Organic Chemistry
• 出版年：2010
• 出版时间：March 5, 2010
• 年：2010
• 卷：75
• 期：5
• 页码：1378-1385
• 全文大小：883K
• 年卷期：v.75,no.5(March 5, 2010)
• ISSN：1520-6904

文摘

The reaction of the benzotriazole N-oxyl radical (BTNO) with a series of 4-X-N,N-dimethylanilines (X = CN, CF₃, CO₂CH₂CH₃, CH₃, OC₆H₅, OCH₃) has been investigated in CH₃CN. Product analysis shows that the radical, 4-X-C₆H₄N(CH₃)CH₂^•, is first formed, which can lead to the N-demethylated product or the product of coupling with BTNO. Reaction rates were found to increase significantly by increasing the electron-donating power of the aryl substituents (ρ⁺ = −3.8). With electron-donating substituents (X = CH₃, OC₆H₅, OCH₃), no intermolecular deuterium kinetic isotope effect (DKIE) and a substantial intramolecular DKIE are observed. With electron-withdrawing substituents (X = CN, CF₃, CO₂CH₂CH₃), substantial values of both intermolecular and intramolecular DKIEs are observed. These results can be interpreted on the basis of an electron-transfer mechanism from the N,N-dimethylanilines to the BTNO radical followed by deprotonation of the anilinium radical cation (ET−PT mechanism). By applying the Marcus equation to the kinetic data for X = CH₃, OC₆H₅, OCH₃ (rate-determining ET), a reorganization energy for the ET reaction was determined (λ_BTNO/DMA = 32.1 kcal mol⁻¹). From the self-exchange reorganization energy for the BTNO/BTNO⁻ couple, a self-exchange reorganization energy value of 31.9 kcal mol⁻¹ was calculated for the DMA^•+/DMA couple.