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- W1980846864 abstract "The photolysis of 3-fluoro-, 3-chloro- and 3-bromoaniline (3-FA, 3-ClA, 3-BrA) in methanol leads to the formation of 3-anisidine and aniline with quantum yields depending on the nature of the halogen. Photosubstitution is the major reaction in the case of 3-FA, but photoreduction also occurs. The latter is more important with 3-BrA than with 3-FA and 3-ClA. Oxygen does not affect the formation of 3-anisidine but reduces that of aniline. Several transients are observed by laser flash photolysis. With each derivative, a broad absorption band with a maximum around 410 nm appears at the end of the pulse. Based on the quenching of oxygen, these bands are assigned to the triplet–triplet absorptions. The anilino radical cation PhNH2+ (λmax=410 and 430 nm) is produced by excitation of the three halogenoanilines. Its formation is not influenced by oxygen. The characteristic absorption of Br2- is observed by irradiation of 3-BrA in the presence of Br- (5×10-3 M). The solvated electron and the long-lived halogenoanilino radical cations (XPhNH2+) are detected. From the quantum yields of aniline, 3-anisidine, PhNH2+ and Br2- formation in the absence and presence of oxygen, the following mechanism can be proposed: 3-anisidine is produced after heterolytic cleavage of the C–X bond from the excited singlet state and addition of MeOH. Aniline is also yielded from the excited singlet state, after heterolytic and/or homolytic cleavage of the C–X bond. In the former case PhNH2+ is formed as an intermediate. With 3-BrA, the homolytic cleavage of the C–Br bond is proved by the formation of Br2-. Me′canisme de la phototransformation des 3-haloge′noanilines en solution me′thanolique. La photolyse des 3-fluoro-, 3-chloro- et 3-bromoaniline (3-FA, 3-ClA et 3-BrA) en solution dans le me′thanol conduit à la formation de 3-anisidine et d'aniline avec des rendements quantiques qui de′pendent de la nature de l'halogène. Dans le cas de la 3-FA la photosubstitution est la principale re′action, mais il se produit e′galement une photore′duction. Cette dernière est plus importante avec la 3-BrA qu'avec les 3-FA et 3-ClA. La pre′sence d'oxygène est sans effet sur la formation de 3-anisidine mais elle de′favorise la formation d'aniline. Plusieurs espèces transitoires ont e′te′ observe′es en photolyse laser. Avec les 3 compose′s une large bande d'absorption ayant un maximum vers 410 nm apparaît juste après l'e′clair. Cette bande disparaît en pre′sence d'oxygène; elle est attribue′e à l'absorption triplet–triplet. Le radical cation aniline PhNH2+ (λmax=410 et 430 nm) apparaît lors de l'irradiation des 3 de′rive′s. Sa formation n'est pas influence′e par l'oxygène. L'absorption caracte′ristique du radical anion Br2- est observe′e lorsque la 3-BrA est irradie′e en pre′sence de Br- (5×10-3 M). L'e′lectron solvate′ et les radicaux cations haloge′noaniline de relative longue dure′e de vie sont de′tecte′s dans tous les cas. La comparaison entre les rendements quantiques de formation d'aniline, de 3-anisidine et des espèces transitoires PhNH2+ et Br2- permet d'expliquer le comportement photochimique des 3-haloge′noanilines de la façon suivante: la formation de 3-anisidine re′sulte d'une coupure he′te′rolytique de la liaison C–X à partir de l'e′tat excite′ singulet, suivie de l'addition de me′thanol, et celle d'aniline d'une coupure he′te′rolytique ou d'une coupure homolytique de la liaison C–X. Dans le premier cas, il se forme interme′diairement le radical cation PhNH2+. L'homolyse a e′te′ mise en e′vidence avec la 3-BrA par de′tection de radicaux Br2- en pre′sence d'ions bromure." @default.
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- W1980846864 date "1999-01-01" @default.
- W1980846864 modified "2023-10-02" @default.
- W1980846864 title "Mechanism of 3-halogenoaniline photolysis in methanol" @default.
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- W1980846864 doi "https://doi.org/10.1039/a902609f" @default.
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