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Photostimulated reactions of haloarenes with benzeneselenate ions by the S RN 1 mechanism. Competition between electron transfer and fragmentation of radical anion intermediates
Author(s) -
Pen̆én̆ory Alicia B.,
Rossi Roberto A.
Publication year - 1990
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610030410
Subject(s) - chemistry , fragmentation (computing) , ion , medicinal chemistry , radical , electron transfer , photochemistry , acetonitrile , reaction mechanism , organic chemistry , catalysis , computer science , operating system
The photostimulated reaction of p ‐iodoanisole ( p ‐IAn) and 2‐bromopyridine with PhSe − ions in liquid ammonia gave Ph 2 Se, ArSePh and Ar 2 Se (Ar = p ‐anisyl, 2‐pyridyl) by the S RN 1 mechanism. These products are formed due to the competition between two steps of the proposed mechanism, the fragmentation of the radical anion intermediate formed in the coupling of aryl radicals with the PhSe − ion, and the electron transfer from the radical anion to an electron acceptor. These photostimulated reactions were carried out in different solvents in order to study their influence on the rates of the two competing reactions. They were also studied at high concentrations of p ‐haloanisoles in acetonitrile (ACN), and it was found that the straightforward substitution product AnSePh was formed only at a 2.5 M concentration of p ‐IAn, 7·8 M p ‐BrAn and 15·6 M p ‐ClAn. The last compound did not react with the PhSe − ion at concentrations as high as 15·6 M , but the substitution reaction took place in the presence of 0·025 M p ‐IAn (entrainment reaction). The relative reactivity of PhSe − vs PhS − toward 2‐quinolyl radicals was studied and it was found that PhSe − reacts 2·7 times faster than PhS − in ACN.