ChemInform Abstract: ELEKTRONEN‐(HYDRIDIONEN)‐UEBERGANG BEI DER PHOTOREDUKTION VON NITROVERBINDUNGEN IN ALKALISCHEN UND NEUTRALEN ALKOHOLISCHEN PUFFERLOESUNGEN

Abstract

Die Photoreduktion substituierter Nitrobenzole unter der Einwirkung von UV‐Licht zu Gemischen substituierter Aniline, Azo‐ und Hydrazobenzole verläuft in wäßrig‐alkoholischen neutralen und alkalischen Puffern glatter als in ungepufferten wäßrigen Alkoholen.

Electron Transfer from Triethylamine to the Triplet State of Dinitronaphthalenes, 4,4‘-Dinitrobiphenyl and 2,7-Dinitrofluorenone: Time Resolved UV−Vis Spectroscopic and Conductometric Study in Polar Solvents

“…Some properties of the triplet state of mono- and dinitronaphthalenes have been reported. , The triplet energy ranges from E T = 190 kJ mol -1 for DNF to 210 kJ mol -1 for 1,4-DNN and further to 240 kJ mol -1 for DNB. , The quantum yield of triplet formation of the dinitroarenes is substantial in solution at room temperature, Φ isc = 0.6−0.8 for 1,3- and 1,4-DNN, and in glassy media at −196 °C. , The quantum yield of singlet oxygen formation (Φ Δ ) as lower limit of Φ isc and further triplet state characteristics are compiled in Table . Φ isc = 0.7 for DNB in methanol has been concluded from results of photoreduction in the presence of MeO - 1 T-T Absorption Maxima, Lifetime, and Relative Triplet Yield, a Rate Constant for Quenching by Oxygen and Quantum Yield of Singlet Oxygen compoundλ TT b (nm)τ T c (μs) k ox (× 10 9 M -1 s -1 )Δ A T /Δ A T max Φ Δ d 1,3-DNN 430 ,550 7 1.1 0.8 0.6 (0.65) 1,4-DNN 410, 550 10 1.2 0.9 0.6 (0.68) 1,5-DNN 410, 540 10 1.2 0.6 0.4 (0.47) 1,8-DNN 400,540 8 1.2 2,3-DNN 470 0.08 <2 0.8 DNB 510 0.14 <2 0.8 DNF 510 10 0.8 1.0 0.6 (0.65) a In argon-saturated acetonitrile.…”

“…Photoreduction of Dinitroarenes in the Presence of 2-Propanol. The major photoproduct of 1,5-DNN in alkaline methanol is 1-amino-5-nitronaphthalene . Concerning the photoreduction of nitronaphthalenes in the presence of alcohols, only a few time-resolved UV−vis spectroscopic measurements have been reported.…”

“…The photoreduction of aromatic compounds by aliphatic amines has been intensively investigated. − Considerable emphasis has been placed on the photoreduction of nitroaromatic compounds. − The photochemistry of 1-methoxy-4-nitronaphthalene depends on the amine and the amount of water in acetonitrile . A related topic is the photoreduction of nitronaphthalenes in the presence of alcohols. , The major photoproduct of 1,5-dinitronaphthalene (1,5-DNN) in alkaline methanol−water (95:5) is 1-amino-5-nitronaphthalene . For the photoinduced electron transfer from triethylamine (TEA) and diethylamine (DEA) to the triplet state of N -phenyl-naphthalimides, two reduction steps, a primary and a secondary electron transfer have been reported .…”

Photochemistry of nitro and nitroso compounds

“…This suggests that the rearrangement possesses a high degree of, if not completely ionic character. The first step, transformation to azoxy acids, does not formally involve a redox process, but has been suggested to occur by an unusual hydrogen atom abstraction from the N-H bond similar to the pathways shown in equations (50) and (57). Since nitro group; are good electron acceptors, it may be reasonable to consider an electron-transfer process as a possible initial step as in equation (79).…”

“…In contrast, the photolyses of 2,4,6-triisopropyl-(equation 53) and 2,3,5,6-tetraisopropyl-nitrobenzenes (equation 54) lead to exclusive a-hydrogen The photoreactions of o-nitrobenzyl derivatives can be interpreted as involving intramolecular hydrogen abstraction from the benzylic position, though no concrete proof is available. It is generally accepted that the ensuing redox processes take place by the sequence shown in equation (57). or a similar one, to yield o-nitrosobenzaldehyde as the primary product.…”