Photochemical n → π^* Excitation of Nitrobenzene

Abstract

The photochemistry of nitrobenzene in isopropyl alcohol has been studied at 366 mp. Evidence for hydrogen abstraction from isopropyl alcohol, following n + a* excitation of nitrobenzene, is presented. Results are consistent with the triplet state of nitrobenzene being the reactive species. Phenylhydroxylamine is generated as the initial product, which oxidizes in air to nitrosobenzene and couples with the latter to form azoxybenzene. The quantum yield for the disappearance of nitrobenzene in degassed solutions was determined to be 1.14 * 0.08 X lo-*. The over-all photochemical reduction of nitrobenzene involves four hydrogen atom abstractions, as evidenced by the ratio of acetone formation to nitrobenzene disappearance.xygen atom transfer has been reported by Hastings 0 and Matsen' to explain the vapor phase photochemistry of nitrobenzene, which results in nitrosobenzene and p-nitrophenol. Chapman2 has reported the photoisomerization of the aromatic nitro group to nitrite ester. Other photochemical studies2+ of aromatic nitro compounds have been reported with emphasis on addition reactions to olefins; however, it is surprising that quantum yield studies for such compounds are lacking. Rebbert and Slagg6 have reported the photochemistry of nitroalkanes, and the quantum yields for these molecules were found to be small compared to unity. With the aim of understanding the photochemistry of aromatic nitro compounds, a quantum yield study of nitrobenzene was undertaken.

Some Electron Spin Resonance Observations in the Photoreduction of Nitrobenzenes

“…results in the present study confirmed the complexity of the solvent effect in the photoreduction of simple aromatic nitro-compounds as suggested by other studies (5,(13)(14)(15) involving product analysis. It is rather unfortunate that the presumably primary radical phN(O)OH which would be expected from hydrogen abstraction of the excited nitrobenzene molecule, was not observed and identified in this study.…”

“…Thus, he reassigned the spectra of the photoparamagnetic intermediate to the radical PhN(0)OH and suggested that the excited nitrobenzene abstracted a hydrogen atom from the solvent as the initial step in the photoreduction of aromatic nitrocompounds. This interpretation has gained general acceptance in the past (5)(6)(7)(8). However, Cowley and Sutcliffe (9) have recently reported some good evidence that the photointermediate in the photolysis of nitrobenzene has the structure P~N ( o ) O R , in which R is the solvent radical.…”

Condensation inhabituelle d'un pyrrole et d'un benzaldéhyde encombré

“…de la cttone 10 et du dinitro-2,6 benzaldthyde. On sait par exemple que le nitrobenzene peut oxyder photochimiquement l'isopropanol en donnant la phCnylhydroxylamine en l'absence d'oxygene, ou le nitrosobenzene en prksence d'oxygene (les arylhydroxylamines s'oxydent spontaniment en nitrosoarenes en prksence d'air) (15,16). Comme la formation de la pyrroline 11 en milieu acide est rtversible, c'est son oxydation par les groupes NO2 de la cttone 10 ou du dinitrobenzaldkhyde, qui provoque la formation irreversible du composC 4.…”

Comparison of photoreactions of flutamide in acetonitrile and 2-propanol solvents in the absence of cage-forming compounds

“…Aromatic nitro compounds are known to undergo various photoreactions, such as photosubstitution, photoredox reactions, photodissociation and photo-induced nitro-nitrite rearrangement [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Photosubstitution and photoredox reactions have been well investigated [1][2][3][4][5][6][7][8][9][10][11], but photodissociation and nitro-nitrite rearrangement have not yet been fully elucidated [10][11][12][13][14][15][16][17].…”

“…Photosubstitution and photoredox reactions have been well investigated [1][2][3][4][5][6][7][8][9][10][11], but photodissociation and nitro-nitrite rearrangement have not yet been fully elucidated [10][11][12][13][14][15][16][17]. Nitro-nitrite rearrangement and photodissociation have low reaction efficiencies, and the short-lived intermediates of these reactions are difficult to observe.…”