Aromatic amines electron-withdrawing groups

J Aromatic Amines—Electron-Withdrawing Grotqrs. Electron-withdrawing groups tend to intensify the positive charge of the anilinium ion, and this destabilizes the ion relative to the amine. This increase the reactivity of an aromatic... 

This is, however, a weak electrophile compared with species such as N02 and will normally only attack highly reactive aromatic compounds such as phenols and amines it is thus without effect on the otherwise highly reactive PhOMe. Introduction of electron-withdrawing groups into the o- or p-positions of the diazonium cation enhances its electrophilic character, however, by increasing the positive charge on the diazo group ... 

In the literature, there are numerous reports regarding the interactions between amines and both electron and proton acceptors132, but less attention has been devoted to interactions between amines and aromatic electron acceptors, in particular when the substrate/amine system is a reacting system, as in the case of nucleophilic aromatic substitution (SjvAr) reactions between amines and substrates activated by nitro or by other electron-withdrawing groups. 

In principle, aliphatic amines may interact as n electron donor molecules towards electron acceptor centres such as aromatic substrates, both homocyclic and heterocyclic, containing electron-withdrawing groups, usually nitro groups. These interactions are mainly electron donor-acceptor (EDA) interactions, in which aromatic amines are considered n or/and tt electron donors. 

This effect is increased if there is a suitable electron-withdrawing group in the ortho or para position on the aromatic ring. Thus, p-nitroaniline and o-nitroaniline have pATa 1-0 and —0.3 respectively. These aromatic amines are thus even weaker bases than aniline, a result of improved delocalization in the free base. The increased basicity of the ortho isomer is a result of the very close inductive effect of the nitro group the meta isomer has only the inductive effect, and its is about 2.5. 

Due to the absence of electron withdrawing groups the aromatic amines are hydrogenated with difficulty. Supported noble metal catalysts (Pd, Pt, Ru, Rh, Ir) are usually active at elevated temperature and pressure. The perhydrogenation of aromatic amines is mainly accompanied by two side reactions, i.e. the... 

Amines and amides can be N-nirra/erf549 with nitric acid,55" N205,551 or N02, 552 and aromatic amines can be converted to triazenes with diazonium salts. Aliphatic primary amines can also be converted to triazenes if the diazonium salts contain electron-withdrawing groups.555 C-Nitrosation is discussed at 1-3 and 2-8. 

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