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The Chemistry of Peroxynitrite: Involvement of an ET Process in the Radical Nitration of Unsaturated and Aromatic Systems
Author(s) -
Grossi Loris,
Montevecchi Pier Carlo,
Strazzari Samantha
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200102)2001:4<741::aid-ejoc741>3.0.co;2-q
Subject(s) - chemistry , nitration , radical , photochemistry , oxime , nitrous acid , benzaldehyde , peroxynitrite , tautomer , medicinal chemistry , organic chemistry , catalysis , enzyme , superoxide
Reactions of peroxynitrous acid, HPN, with styrene under acidic conditions lead to the oxime 1 , the nitrate 2 , benzaldehyde ( 3 ), and α‐nitroacetophenone ( 4 ) in overall yields that depend strongly on the pH value and with a product distribution that depends on the dioxygen concentration. The results are rationalized by assuming that HPN undergoes acid‐catalyzed decomposition to give nitrous anhydride, or its synthetic equivalent, which is responsible for the regioselective nitration of the styrene double bond by an ET process. The resulting β‐nitrobenzyl radical 6 can, depending on the reaction conditions, undergo reversible coupling with nitric oxide to afford the nitroso derivative 7 and then the tautomeric oxime 1 , or trapping by dioxygen, eventually leading to products 2 , 3 , and 4 through the intermediacy of the peroxynitrite derivative 8 . Oxime 1 and nitrate 2 are also obtained by treating styrene with nitrous anhydride under protic conditions, the latter being produced in situ from nitric oxide/dioxygen. Similarly to styrene, 1,4‐diphenylbutadiene ( 14 ) gives radicals 22 and 21 by competitive trapping at the side chain and at the aromatic ring. In turn, radicals 22 and 21 undergo β‐fragmentation reactions or trapping by dioxygen with eventual formation of nitrates 16 and 17 , cinnamic aldehyde ( 18 ), and the diol 15 . Finally, the HPN‐promoted reaction of p ‐cresol ( 27 ) leads to the 2‐nitro derivative 28 through an initial electron‐transfer process followed by in cage recombination of the resulting radical ion pair.