The reaction of 1,2-Dichloro-4,5-dinitrobenzene with hydroxide ion: roles of meisenheimer complexes and radical pairs

• Autor(a) principal: Blaskó,Andrei
• Data de Publicação: 2013
• Outros Autores: Bunton,Clifford A., Gillitt,Nichollas D., Bacaloglu,Radu, Yunes,Santiago F., Zucco,César
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Journal of the Brazilian Chemical Society (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532013000700008
• topic: aromatic nucleophilic substitution; Meisenheimer complexes

The reaction of 1,2-dichloro-4,5-dinitrobenzene (DCDNB) with aqueous OH- produces (after acidification) 2-nitro-4,5-dichlorophenol with loss of NO2. Nevertheless, with > 2 mol L-1 OH-, only DCDNB was recovered due to the formation of the long-lived 3,6-dihydroxy Meisenheimer complex (M2-), and that in acid, reverted to the starting material. Fast formation of monohydroxy Meisenheimer complex (M1-) can be followed in DMSO:H2O 7:3 v/v and rate constants for its interconversion with DCDNB and for formation and return with M2- complex were estimated, with evidence for these reactions in DMSO:H2O 1:1 v/v and H2O. The rapid hydrogen exchange in OD- /D2O limits the use of¹ H nuclear magnetic resonance (NMR) spectroscopy in identifying intermediates. ¹ H and13 C NMR signals of M2- complex were observed in DMSO-H2O-KOH. There is evidence for the formation of free radicals in DMSO:H2O 4:1 v/v, and overall kinetics in more aqueous medium were treated in terms of the transient existence of anionic radical pairs.