Amines as leaving groups in nucleophilic aromatic substitution reactions. Part 4.1 σ-Adduct formation in the hydrolysis of 1-amino-2,4,6-trinitrobenzenes

The kinetic study of the reaction of 2,4,6-trinitro-1-pyrrolidinobenzene 3, 2,4,6-trinitro-1-piperidinobenzene 1 and 1-morpholino-2,4,6-trinitrobenzene 2 was made in 1,4-dioxane–water mixtures at 25 °C. In all cases, several processes were observed, the slowest of them leading to the formation of picrate ion. The fastest processes involved the formation of σ complexes by addition of one or two HO− to unsubstituted ring positions and the ionisation of the 1∶1 complex. Besides, for compounds 1 and 3, cis–trans isomerisation of 1∶2 complexes was kinetically detected. Substitution occurred by displacement of the amino group on the substrate and the 1∶1 complex. The reaction pathway for the formation of phenol which involves the formation of these complexes has lower energy than that which results from addition to the 1 position of the substrate.