ABSTRACT
Substitution of aromatic compounds is most commonly effected by electrophiles. Substitution occurs in two stages. The electrophile adds to one carbon atom of the nucleus, giving a carbocation intermediate, and a proton is then eliminated from the adduct. The rate-determining step in most electrophilic addition reactions is the addition of the electrophile to the aromatic ring. Furan is aromatic and undergoes electrophilic substitution at low temperature. Any substituent that donates electrons, therefore, increases the reactivity; likewise, electron- withdrawing substituents decrease the reaction rate. Reduction of the carbonyl is followed by intramolecular Friedel–Crafts reaction to complete the skeleton. In the presence of concentrated acid, the nitrogen of dimethylaniline is stoichiometrically protonated and hence electron withdrawing, directing nitration meta. In the absence of concentrated acid, a small concentration of the highly reactive free base undergoes ortho/para-substitution, the para isomer being predominant.
