Comportement photochimique du 4-nitrosophénol en solution aqueuse

Abstract

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.

Dimerization of Aromatic C-Nitroso Compounds

“…For example, the crystal structure of cis -azodioxybenzene was first reported in 1970 . It is important to note that some nitrosoarenes, such as 4-nitrosophenol and its derivatives, do not typically form dimers, in part because they commonly engage in tautomerism to give other structures, as illustrated by the formation of the monoxime of 1,4-benzoquinone in eq . − …”

Oxidation and Nitrosation in the Nitrogen Monoxide/Superoxide System

“…Quantitation of 4-Nitrosophenol by UV/Vis Spectroscopy and HPLC-The formation of 4-nitrosophenolate (pK Ϸ 6) in reactions of phenol (5 mM) with SIN-1 (200 M) and/or spermine NONOate (100 M) was monitored spectrophotometrically at 400 versus 500 nm over a time period of 2 h in 0.1 M potassium phosphate buffer at pH 7.4 and 37°C (37). Its yield in these samples was determined by HPLC as described previously (38).…”