Nucleophilic Attack on Aromatic Speciesfrom the nucleus was sufficiently great (cf. the addition of nucleo
philes to alkenes carrying electron-withdrawing substituents, p. 153).
In fact, nitrobenzene can be fused with potash, in the presence of air,
to yield o-nitrophenol (XXVIII):
W(XXVIII)The nitro-group is able to stabilise the anionic intermediate (XXIX)
by delocalising its charge if eOH enters the o- or p-positions but not
if it goes into the m-positiom The o-attack is likely to be preferred,
despite the size of the adjacent N0 2 , as the inductive effect of the
ilitro-group, acting over a shorter distance, will make the o-position
more electron-deficient than the p-. The overall reaction is exactly
what we should expect, namely that a substituent promoting attack
on the m-position by an electrophile would promote o/p-attack by a
nucleophile.
Once (XXIX) has been formed, it can eliminate eOH (i) and so be
reconverted to nitrobenzene as readily as it can eliminate He (ii) to
yield the product (XXVIII). To drive the reaction over to the right an
oxidising agent must be present to encourage the elimination of
hydride ion and to destroy it as«formed. Thus the fusion is either
carried out ii^the air, or an oxidising agent such as potassium
nitrate or ferricyanide is added.
Pyridine behaves in an exactly analogous manner undergoing
attack by sodamide (i.e. eNH 2 , the Tschitschibabin reaction), to