Mechanism of base catalysis in the reactions of phenyl aryl ethers with aliphatic amines in dimethyl sulfoxide

Abstract

The reactions of n-butylamine, pyrrolidine and piperidine with phenyl 2,4,6-trinitrophenyl ether, 3, in DMSO result in the rapid reversible formation of adducts by reaction at the 3-position followed by attack at the 1-position leading to substitution of the phenoxy group. With phenyl 2,4-dinitronaphthyl ether, 1a, and phenyl 2,4-dinitrophenyl ether, 8, substitution is the only process observed. For each substrate reactions with n-butylamine show a first order dependence on the amine concentration indicating that nucleophilic attack is rate-limiting. However, the reactions with pyrrolidine and with piperidine are subject to general base catalysis and it is argued that here the deprotonation of the initially formed zwitterionic intermediates is rate determining. The results are compared and contrasted with those of the corresponding ethyl ethers, where base catalysis involves the SB-GA mechanism, and with phenyl sulfides.