Photooxygenation of nitrobenzyl derivatives. Mechanisms of photogeneration and hydrolysis of α-hydroperoxy nitrobenzyl ethers

Abstract

Can. J. Chem. 65, 1775 (1987. ' The photooxygenation of nitrobenzyl derivatives 1-10 has been studied in aqueous solution as a function of pH. For m-nitrobenzyl ethers 2-4 and 9, stable a-hydroperoxy ethers (11)(12)(13) are the primary photochemical products. Acid hydrolysis of 11-13 gives m-nitrobenzaldehyde and hydrogen peroxide. Quantum yields for photooxygenation are reported for a number of derivatives as a function of pH. Acid and base catalyses of photooxygenation are observed for several compounds. A mechanism involving photogenerated nitrobenzyl carbanion intermediates is proposed.PETER WAN, S . MURALIDHARAN, IAIN MCAULEY et CHRISTOPHER A. BABBAGE. Can. J. Chem. 65, 1775 (1987. Operant en solutions aqueuses, on a CtudiC la photo-oxydation des dCrivCs nitrobenzyliques (1-10) en fonction du pH. Dans les cas des Cthers m-nitrobenzyliques (2-4 et 9), les produits photochimiques primaires sont les Cthers a-hydroperoxylCs stables (11-13). L'hydrolyse acide des composCs 11-13 conduit au m-nitrobenzaldkhyde et au peroxyde d'hydroghe. Dans les cas d'un certain nombre de derives, on rapporte les rendements quantiques pour la photo-oxygenation en fonction du pH.Dans les cas de plusieurs composCs, on a observe que la photo-oxygenation est soumise i une catalyse acidelbase. On propose un mCcanisme impliquant, comme intermkdiaires, des carbanions nitrobenzyliques gCnCrCs photochimiquement.[Traduit par la revue]The photochemistry of aliphatic and aromatic nitro compounds has received considerable attention and several reviews (1-4) have been published. Recently, we (5-7) and others (8, 9) have noted that some m-and p-nitro-substituted benzenes display unexpected reactivity when irradiated in aqueous solution, especially in the presence of hydronium and hydroxide ions as catalysts for the transformations (5-8). Whereas it is well known (1-4) that o-nitrobenzyl systems are photolabile due to the proximity to the substituent of the reacting nitro chromophore, resulting in initial intramolecular hydrogen abstraction via the n, T" triplet excited state, it had been assumed for many years that the corresponding meta and para derivatives should not be photolabile, except for simple photoreduction. However, in aqueous solution, a number of m-and p-nitro-substituted derivatives have been found to react via new photochemical processes (5-9). In a preliminary report (10) we had demonstrated that molecular oxygen can react with photoexcited nitrobenzyl derivatives, which represent an additional example of the rich and sometimes unpredictable photochemistry of m-and p-substituted nitroaromatic compounds. In this work, we report the generality and proposed mechanisms for the photooxygenation reaction of a variety of m-and p-nitro-substituted derivatives. In addition, the thermal aqueous chemistry of several photogenerated a-hydroperoxy m-nitrobenzyl ethers isolated in these studies will be presented. Results Product studiesThe compounds chosen for the study, 1-10, are shown below. Both m-and p-nitrobenzyl alcohols 1 and 7, respec...

Highly selective, economical and efficient oxidation of alcohols to aldehydes and ketones by air and sunlight or visible light in the presence of porphyrins sensitizers

“…Furthermore, independent photolysis of hydroperoxymethanol 2 in CH 3 CN results in the formation of 3, which is the only product. 20 Compound 3 decomposes further to the final product 4 and hydrogen peroxide which is a by-product.…”

Oxidation of Benzylic Alcohols and Ethers to Carbonyl Derivatives by Nitric Acid in Dichloromethane

“…[54] Benzyl methyl ethers were almost exclusively prepared by the classical Williamson synthesis, by treatment of an MeOH solution of the appropriate halide (100.0 mmol in 100 mL) with MeONa in MeOH (200 mmol in 100 mL), by a described procedure (Method A). [55] 1-(Methoxymethyl)-3-methylbenzene (1c, 11.02 g, 81% from the chloride), [56] 1-(1,1-dimethylethyl)-4-(methoxymethyl)benzene (1e, 14.60 g, 82% from the bromide), [57] 1-chloro-2-(methoxymethyl)benzene (1f, 11.70 g, 75% from the chloride), [58] 1-chloro-3-(methoxymethyl)benzene (1g, 12.48 g, 80% from the chloride), [58] 1-chloro-4-(methoxymethyl)benzene (1h, 12.17 g, 78% from the chloride), [59] 1,3-dichloro-4-(methoxymethyl)benzene (1j, 17.57 g, 92% from the chloride), [60] 1-(methoxymethyl)-2-nitrobenzene (1k, 12.53 g, 75% from the iodide), [61] 1-(methoxymethyl)-3-nitrobenzene (1m, 13.03 g, 78% from the iodide), [62] 1-(methoxymethyl)-4-nitrobenzene (1n, 12.69 g, 76% from the iodide), [62] and diphenylmethyl methyl ether (1hh, 17.62 g, 89% from the chloride) [63] were prepared by Method A. [(1,1-Dimethylethoxy)methyl]benzene [64] (1dd, 7.22 g, 44%) was prepared in a similar way, from benzyl bromide and potassium tert-butoxide.…”

Oxidation of benzoins to benzils in the presence of porphyrin sensitizers by air and sunlight or visible light

“…Thus, in the presence of H 2 TMP formation singlet oxygen, there may be a new photochemical pathway that involves the overall insertion of molecular oxygen into the C-H bond of the alcohols 1 to form benzoins 2. Furthermore, independent photolysis of 2-hydroperoxy-2-hydroxy-1,2-diphenylethanone 2 in CH 3 CN results in the formation of 3, which is the only product [95,96,102]. Compound 3 decomposes further to the final product 4 and hydrogen peroxide which is a by-product.…”