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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1998
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Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00318655_v67_n5_p487_Murgida http://hdl.handle.net/20.500.12110/paper_00318655_v67_n5_p487_Murgida |
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paper:paper_00318655_v67_n5_p487_Murgida2023-06-08T14:57:18Z Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study Murgida, Daniel Horacio Aramendía, Pedro Francisco Erra Balsells, Rosa 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. 1998 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00318655_v67_n5_p487_Murgida 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. |
author |
Murgida, Daniel Horacio Aramendía, Pedro Francisco Erra Balsells, Rosa |
spellingShingle |
Murgida, Daniel Horacio Aramendía, Pedro Francisco Erra Balsells, Rosa Benzophenone-Photosensitized Reactions of Xanthinic Compounds. A Mechanistic Study |
author_facet |
Murgida, Daniel Horacio Aramendía, Pedro Francisco Erra Balsells, Rosa |
author_sort |
Murgida, Daniel Horacio |
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 |
publishDate |
1998 |
url |
https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00318655_v67_n5_p487_Murgida http://hdl.handle.net/20.500.12110/paper_00318655_v67_n5_p487_Murgida |
work_keys_str_mv |
AT murgidadanielhoracio benzophenonephotosensitizedreactionsofxanthiniccompoundsamechanisticstudy AT aramendiapedrofrancisco benzophenonephotosensitizedreactionsofxanthiniccompoundsamechanisticstudy AT errabalsellsrosa benzophenonephotosensitizedreactionsofxanthiniccompoundsamechanisticstudy |
_version_ |
1768545318646841344 |