Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study

Photosensitized reaction of xanthinic compounds (XH) as caffeine (CF), theobromine (TB) and theophylline (TF) by benzophenone (BZ) in ethanol solution was investigated. In the three cases four main reaction products (benzopinacol; diphenylcarbinol; 1,1-diphenyl-1,2-propanediol and 8-[1-(1-hydroxyeth...

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Autores principales: Murgida, D.H., Aramendía, P.F., Erra-Balsells, R.
Formato: JOUR
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_00318655_v67_n5_p487_Murgida
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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_00318655_v67_n5_p487_Murgida2023-10-03T14:41:33Z Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study Murgida, D.H. Aramendía, P.F. Erra-Balsells, R. Photosensitized reaction of xanthinic compounds (XH) as caffeine (CF), theobromine (TB) and theophylline (TF) by benzophenone (BZ) in ethanol solution was investigated. In the three cases four main reaction products (benzopinacol; diphenylcarbinol; 1,1-diphenyl-1,2-propanediol and 8-[1-(1-hydroxyethyl)] xanthine) were identified and then characterized by melting point, 1H NMR, 13C NMR and mass spectrometry. The quenching of triplet BZ by the three XH was detected and a thorough kinetic analysis was performed. Caffeine produces mainly physical quenching, while TF reacts by N-H hydrogen abstraction. For TB both mechanisms are operative. Heats of reactions were calculated for chosen reactive steps of the mechanism by the PM3 method. They provide additional support to the proposed reaction scheme. We demonstrate that the mechanism leading to XP formation does not proceed through the X• radical directly obtained by H abstraction. An alternative reaction path through an intermediate radical originated on the addition of ethanol radical to XH is proposed. Redox potentials for the oxidation of XH were estimated by cyclic voltametry and by using the Rehm-Weller equation the redox quenching of triplet BZ by XH was discarded. Fil:Murgida, D.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Aramendía, P.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Erra-Balsells, R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00318655_v67_n5_p487_Murgida
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
description Photosensitized reaction of xanthinic compounds (XH) as caffeine (CF), theobromine (TB) and theophylline (TF) by benzophenone (BZ) in ethanol solution was investigated. In the three cases four main reaction products (benzopinacol; diphenylcarbinol; 1,1-diphenyl-1,2-propanediol and 8-[1-(1-hydroxyethyl)] xanthine) were identified and then characterized by melting point, 1H NMR, 13C NMR and mass spectrometry. The quenching of triplet BZ by the three XH was detected and a thorough kinetic analysis was performed. Caffeine produces mainly physical quenching, while TF reacts by N-H hydrogen abstraction. For TB both mechanisms are operative. Heats of reactions were calculated for chosen reactive steps of the mechanism by the PM3 method. They provide additional support to the proposed reaction scheme. We demonstrate that the mechanism leading to XP formation does not proceed through the X• radical directly obtained by H abstraction. An alternative reaction path through an intermediate radical originated on the addition of ethanol radical to XH is proposed. Redox potentials for the oxidation of XH were estimated by cyclic voltametry and by using the Rehm-Weller equation the redox quenching of triplet BZ by XH was discarded.
format JOUR
author Murgida, D.H.
Aramendía, P.F.
Erra-Balsells, R.
spellingShingle Murgida, D.H.
Aramendía, P.F.
Erra-Balsells, R.
Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study
author_facet Murgida, D.H.
Aramendía, P.F.
Erra-Balsells, R.
author_sort Murgida, D.H.
title Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study
title_short Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study
title_full Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study
title_fullStr Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study
title_full_unstemmed Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study
title_sort benzophenone-photosensitized reactions of xanthinic compounds. a mechanistic study
url http://hdl.handle.net/20.500.12110/paper_00318655_v67_n5_p487_Murgida
work_keys_str_mv AT murgidadh benzophenonephotosensitizedreactionsofxanthiniccompoundsamechanisticstudy
AT aramendiapf benzophenonephotosensitizedreactionsofxanthiniccompoundsamechanisticstudy
AT errabalsellsr benzophenonephotosensitizedreactionsofxanthiniccompoundsamechanisticstudy
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