Base catalysis in nucleophilic aromatic substitution reactions: evidence for cyclic transition state mechanism over the dimer mechanism in a non-polar aprotic solvent

Abstract

The reactions of X-phenyl 2,4,6-trinitrophenyl ethers [X = 2-NO₂, 3-NO₂, 4-NO₂, 2,4-(NO₂)₂, 3,4-(NO₂)₂, 2,5-(NO₂)₂, and 2,6-(NO₂)₂] with aniline in benzene display three distinct mechanisms even though all except the 2,6-dinitrophenyl ether are base catalysed. The catalysis of the mononitro-substituted ethers involves two aniline molecules and proceeds at a temperature-independent rate in the temperature range 5–35 °C while that of the dinitro-substituted ones involves only one aniline molecule and proceeds at a temperature-dependent rate over the same temperature range. The results are interpreted in terms of a cyclic mechanism involving four-, six-, and eight-membered rings in the transition state.