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Quinone‐sensitized Steady‐state Photolysis of Acetophenone Oximes Under Aerobic Conditions: Kinetics and Product Studies †
Author(s) -
Park Adriana,
Kosareff Nicole M.,
Kim Jason S.,
Peter de Lijser H. J.
Publication year - 2006
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2005-04-23-ra-496
Subject(s) - chemistry , radical , acetophenone , photochemistry , oxime , nucleophile , hydrogen atom abstraction , electron transfer , hydroxyl radical , radical ion , medicinal chemistry , organic chemistry , ion , catalysis
Oxidation of oximes via photosensitized electron transfer (PET) results in the formation of the corresponding ketones as the major product via oxime radical cations and iminoxyl radicals. The influence of electron‐releasing and electron‐accepting substituents on these reactions was studied. The observed substituent effect strongly supports formation of iminoxyl radicals from the oximes via an electron transfer–proton transfer sequence rather than direct hydrogen atom abstraction. Correlation of the relative conversion of the oximes with Hammett parameters shows that radical effects dominate for the meta ‐substituted acetophenone oximes (ρ rad /ρ pol = 5.4; r 2 = 0.93), whereas the para ‐substituted oximes are influenced almost equally by radical and ionic effects (ρ rad /ρ pol = ‐1.1; r 2 = 0.98). From these data sets we conclude that the follow‐up reactions proceed through a number of intermediates with both radical and ionic character. This was confirmed by product studies with the use of an isotopically labeled nucleophile. In addition to the major oxidation product (ketone), a chlorine‐containing product was often identified as well. Studies on the formation of this product show that the most likely pathway is either via a direct nucleophilic addition in a complex formed between the oxime radical cation and the chloranil radical anion or via a radical substitution (S H 2) mechanism. These studies show that with the increasing use of oximes as drugs and pesticides, intake of these chemicals followed by enzymatic oxidation may result in the formation of a variety of reactive intermediates, which may lead to cell and tissue damage.