Photochemical reaction mechanisms of 2-nitrobenzyl compounds: 2-nitrobenzyl alcohols form 2-nitroso hydrates by dual proton transfer.
Irradiation of 2-nitrobenzyl alcohol (1, R = H) and 1-(2-nitrophenyl)ethanol (1, R = Me) in various solvents yields 2-nitroso benzaldehyde (4, R = H) and 2-nitroso acetophenone (4 R = Me), respectively, with quantum yields of about 60%. The mechanism of this reaction, known since 1918, was investigated using laser flash photolysis, time-resolved infrared spectroscopy (TRIR), and 18O-labeling experiments. The primary aci-nitro photoproducts 2 react by two competing paths. The balance between the two depends on the reaction medium. Reaction via hydrated nitroso compounds 3 formed by proton transfer prevails in aprotic solvents and in aqueous acid and base. In water, pH 3-8, the classical mechanism of cyclization to benzisoxazolidine intermediates 5, followed by ring opening to carbonyl hydrates 6, predominates. The transient intermediates 3 and 6 were identified by TRIR. Potential energy surfaces for these reactions were mapped by density functional calculations.
Gaplovsky
Martin
M
Departement Chemie der Universität Basel, Klingelbergstr. 80, CH-4056 Basel, Switzerland.
Il'ichev
Yuri V
YV
Kamdzhilov
Yavor
Y
Kombarova
Svetlana V
SV
Mac
Marek
M
Schwörer
Markus A
MA
Wirz
Jakob
J
D001592:Benzyl Alcohols / Q000138:chemical synthesis*; D006863:Hydrogen-Ion Concentration; D007834:Lasers; D015394:Molecular Structure; D009578:Nitrobenzenes / Q000138:chemical synthesis / Q000737:chemistry*; D009603:Nitroso Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010777:Photochemistry; D010782:Photolysis; D011522:Protons; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared / Q000379:methods; D014466:Ultraviolet Rays
D001592:Benzyl Alcohols; D009578:Nitrobenzenes; D009603:Nitroso Compounds; D011522:Protons; C046887:2-nitrobenzyl alcohol