Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen

The oxidation of diethyl and diphenyl sulfide photosensitized by dicyanoanthracene (DCA), N-methylquinolinium tetrafluoroborate (NMQ +), and triphenylpyrylium tetrafluoroborate (TPP+) has been explored by steady-state and laser flash photolysis studies in acetonitrile, methanol, and 1,2-dichloroetha...

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Autores principales: Bonesi, S.M., Manet, I., Freccero, M., Fagnoni, M., Albini, A.
Formato: JOUR
Materias:
Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Acetonitrile
Electron transitions
Negative ions
Photolysis
Photosensitivity
Quenching
Sulfoxidation
Sulfur compounds
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_09476539_v12_n18_p4844_Bonesi
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling todo:paper_09476539_v12_n18_p4844_Bonesi2023-10-03T15:49:24Z Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen Bonesi, S.M. Manet, I. Freccero, M. Fagnoni, M. Albini, A. Electron transfer oxidation Photochemistry reaction mechanisms Sulfides Acetonitrile Electron transitions Negative ions Photolysis Photosensitivity Quenching Electron transfer oxidation Photochemistry reaction mechanisms Sulfides Sulfoxidation Sulfur compounds The oxidation of diethyl and diphenyl sulfide photosensitized by dicyanoanthracene (DCA), N-methylquinolinium tetrafluoroborate (NMQ +), and triphenylpyrylium tetrafluoroborate (TPP+) has been explored by steady-state and laser flash photolysis studies in acetonitrile, methanol, and 1,2-dichloroethane. In the Et2S/DCA system sulfide-enhanced intersystem crossing leads to generation of 1O2, which eventually gives the sulfoxide via a persulfoxide ; this mechanism plays no role with Ph2S, though enhanced formation of 3DCA has been demonstrated. In all other cases an electron-transfer (ET) mechanism is involved. Electron-transfer sulfoxidation occurs with efficiency essentially independent of the sulfide structure, is subject to quenching by benzoquinone, and does not lead to Ph2SO cooxidation. Formation of the radical cations R2S.+ has been assessed by flash photolysis (medium-dependent yield, dichloroethane ≫ CH3CN > CH3OH) and confirmed by quenching with 1,4-dimethoxybenzene. Electron-transfer oxidations occur both when the superoxide anion is generated by the reduced sensitizer (DCA.-, NMQ.) and when this is not the case (TPP.). Although it is possible that different mechanisms op erate with different ET sensitizers, a plausible unitary mechanism can be proposed. This considers that reaction between R2S.+ and O2.- mainly involves back electron transfer, whereas sulfoxidation results primarily from the reaction of the sulfide radical cation with molecular oxygen. Calculations indeed show that the initially formed fleeting complex RS2 +⋯O-O. adds to a sulfide molecule and gives strongly stabilized R2S-O.-+O-SR2 via an accessible transition state. This intermediate gives the sulfoxide, probably via a radical cation chain path. This mechanism explains the larger scope of ET sulfoxidation with respect to the singlet-oxygen process. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_09476539_v12_n18_p4844_Bonesi
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Acetonitrile
Electron transitions
Negative ions
Photolysis
Photosensitivity
Quenching
Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Sulfoxidation
Sulfur compounds
spellingShingle Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Acetonitrile
Electron transitions
Negative ions
Photolysis
Photosensitivity
Quenching
Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Sulfoxidation
Sulfur compounds
Bonesi, S.M.
Manet, I.
Freccero, M.
Fagnoni, M.
Albini, A.
Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
topic_facet Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Acetonitrile
Electron transitions
Negative ions
Photolysis
Photosensitivity
Quenching
Electron transfer oxidation
Photochemistry reaction mechanisms
Sulfides
Sulfoxidation
Sulfur compounds
description The oxidation of diethyl and diphenyl sulfide photosensitized by dicyanoanthracene (DCA), N-methylquinolinium tetrafluoroborate (NMQ +), and triphenylpyrylium tetrafluoroborate (TPP+) has been explored by steady-state and laser flash photolysis studies in acetonitrile, methanol, and 1,2-dichloroethane. In the Et2S/DCA system sulfide-enhanced intersystem crossing leads to generation of 1O2, which eventually gives the sulfoxide via a persulfoxide ; this mechanism plays no role with Ph2S, though enhanced formation of 3DCA has been demonstrated. In all other cases an electron-transfer (ET) mechanism is involved. Electron-transfer sulfoxidation occurs with efficiency essentially independent of the sulfide structure, is subject to quenching by benzoquinone, and does not lead to Ph2SO cooxidation. Formation of the radical cations R2S.+ has been assessed by flash photolysis (medium-dependent yield, dichloroethane ≫ CH3CN > CH3OH) and confirmed by quenching with 1,4-dimethoxybenzene. Electron-transfer oxidations occur both when the superoxide anion is generated by the reduced sensitizer (DCA.-, NMQ.) and when this is not the case (TPP.). Although it is possible that different mechanisms op erate with different ET sensitizers, a plausible unitary mechanism can be proposed. This considers that reaction between R2S.+ and O2.- mainly involves back electron transfer, whereas sulfoxidation results primarily from the reaction of the sulfide radical cation with molecular oxygen. Calculations indeed show that the initially formed fleeting complex RS2 +⋯O-O. adds to a sulfide molecule and gives strongly stabilized R2S-O.-+O-SR2 via an accessible transition state. This intermediate gives the sulfoxide, probably via a radical cation chain path. This mechanism explains the larger scope of ET sulfoxidation with respect to the singlet-oxygen process. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.
format JOUR
author Bonesi, S.M.
Manet, I.
Freccero, M.
Fagnoni, M.
Albini, A.
author_facet Bonesi, S.M.
Manet, I.
Freccero, M.
Fagnoni, M.
Albini, A.
author_sort Bonesi, S.M.
title Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
title_short Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
title_full Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
title_fullStr Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
title_full_unstemmed Photosensitized oxidation of sulfides: Discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
title_sort photosensitized oxidation of sulfides: discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen
url http://hdl.handle.net/20.500.12110/paper_09476539_v12_n18_p4844_Bonesi
work_keys_str_mv AT bonesism photosensitizedoxidationofsulfidesdiscriminatingbetweenthesingletoxygenmechanismandelectrontransferinvolvingsuperoxideanionormolecularoxygen
AT maneti photosensitizedoxidationofsulfidesdiscriminatingbetweenthesingletoxygenmechanismandelectrontransferinvolvingsuperoxideanionormolecularoxygen
AT freccerom photosensitizedoxidationofsulfidesdiscriminatingbetweenthesingletoxygenmechanismandelectrontransferinvolvingsuperoxideanionormolecularoxygen
AT fagnonim photosensitizedoxidationofsulfidesdiscriminatingbetweenthesingletoxygenmechanismandelectrontransferinvolvingsuperoxideanionormolecularoxygen
AT albinia photosensitizedoxidationofsulfidesdiscriminatingbetweenthesingletoxygenmechanismandelectrontransferinvolvingsuperoxideanionormolecularoxygen
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