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Transfer Hydrogenation of Nitro‐, Nitroso‐ and Azoarenes by Homolytic Retrodisproportionation
Author(s) -
Coellen Michael,
Rüchardt Christoph
Publication year - 1995
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19950010811
Subject(s) - homolysis , xanthene , chemistry , reactivity (psychology) , photochemistry , nitroso , nitro , radical , medicinal chemistry , tetralin , heterolysis , hydrogen atom , organic chemistry , catalysis , alkyl , medicine , alternative medicine , pathology
Nitro‐, nitroso‐ and azobenzene are reduced almost quantitatively to aniline when heated to 230–300°C with 9,10‐dihydroanthracene (DHA), xanthene or tetralin. From the effect of polar substituents and polar solvents on the reactivity and from the isotope effect k H / k D ≈ 2.4 (280°C), a hydrogen‐atom transfer from the H donor to the acceptor ( retrodisproportionation ) is proposed as the rate‐determining step. The lower reactivity of xanthene compared with 9,10‐dihydroanthracene eliminates the possibility of a rate‐determining hydride transfer. The observation of an intense ESR signal of 9‐xanthyl radicals during the reaction in diphenyl ether and the typical products support the proposed homolytic mechanism.