The nucleophilic aromatic substitution of pentachloronitrobenzene (PCNB) with benzenethiolate and benzeneselenide anions in aqueous solution give rise to fast nitro group substitution in both cases. In the same conditions, pentafluoronitrobenzene (PFNB) and 3,4,5-trichloronitrobenzene (TCNB) undergo substitution of the halogen atom placed in para position with respect to the nitro group. Mechanistic studies suggest that the reactions of PCNB and PFNB (substitution of very electronegative leaving groups) follow a mechanism that includes a "polar" attack of the nucleophile on the aromatic substrate in the first step and a fast "radical" evolution of the o-complex intermediate. On the other hand, the chloride substitution in the TCNB reactions follows the classical SNAr mechanism. The photochemical reactions of PCNB, PFNB and TCNB in the presence of nucleophiles (electron donors) lead in all cases to photoreduction products (anilines) probably through the aromatic radical anion. © Springer-Verlag 1996.
|Journal||Anales de Quimica|
|Publication status||Published - 1 Dec 1996|
- Nucleophilic Aromatic Substitution