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Photochemical reaction mechanisms of 2-nitrobenzyl compounds: 2-Nitrobenzyl alcohols form 2-nitroso hydrates by dual proton transfer

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Abstract

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.

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Authors and Affiliations

  1. Departement Chemie der Universität Basel, Klingelbergstr. 80, CH-4056, Basel, Switzerland

    Martin Gaplovsky, Yuri V. Il’ichev, Yavor Kamdzhilov, Svetlana V. Kombarova, Marek Mac, Markus A. Schwörer & Jakob Wirz

  2. Department of Chemistry, Wichita State University, 317 McKinley Hall, 1845 Fairmount, Wichita, KS, 67260-0051, USA

    Yuri V. Il’ichev & Svetlana V. Kombarova

  3. Jagiellonian University, Krakow, Poland

    Marek Mac

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  1. Martin Gaplovsky
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  2. Yuri V. Il’ichev
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  3. Yavor Kamdzhilov
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Correspondence to Yuri V. Il’ichev.

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Dedicated to Professor Hiroshi Masuhara on the occasion of his 60th birthday.

Electronic supplementary information (ESI) available: Coordinates and energies of all optimised structures, original rate data and calculated frequencies. See http://www.rsc.org/suppdata/pp/b4/b409927c/

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Gaplovsky, M., Il’ichev, Y.V., Kamdzhilov, Y. et al. Photochemical reaction mechanisms of 2-nitrobenzyl compounds: 2-Nitrobenzyl alcohols form 2-nitroso hydrates by dual proton transfer. Photochem Photobiol Sci 4, 33–42 (2005). https://doi.org/10.1039/b409927c

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