RksumC : En milieu acide (pH = 1) le 4-nitrosophCno1 irradiC entre 296 et 366 nm se transforme majoritairement (75580%) en benzoquinone. Le rendement quantique de cette reaction depend de la longueur d'onde : il est environ 6 fois plus Clevt k 365 nm qu'k A 5 313 nm. Ce phtnomkne est attribut k un Cquilibre tautomtrique entre les formes nitroso et quinone monooxime, la premikre Ctant photochimiquement beaucoup plus rtactive que la seconde. Dans l'eau distillee non tamponnCe (pH = 5-6), il apparait une espkce intermediaire qui prCsente en CLHP un temps de retention voisin de celui de la benzoquinone et dont le maximum d'absorption est situk ? I 235 nm. La transformation de cet intermkdiaire est acctltrCe en milieu acide.Mots elks : photochimie, 4-nitrosophCno1, effet de longueur d'onde.
Abstract:In acidic medium (pH = 1) 4-nitrosophenol irradiated in the range 296-366 nm is mainly transformed into benzoquinone (75-80%). The quantum yield of this reaction is wavelength dependent: it is about 6 times higher at 365 nm than at A 5 3 13 nm. This phenomenon is attributed to an equilibrium between two tautomeric forms, nitroso and quinone monooxime, the former being much more photoreactive than the latter. In unbuffered aqueous solution (pH = 5 4 ) the formation of an intermediate is observed. Its HPLC retention time is just a little shorter than that of benzoquinone and the maximum of its absorption band is located at 235 nm. The rate of transformation of this intermediate increases with decreasing pH.
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