Studies Pof the Mechanism of Chlorination of Indoles. Detection of iV-Chloroindole and 3-Chloro-3ii-indole as Intermediates

N-Chloroindole was stable at low concentration and temperature in nonprotic solvents. It rearranged in alkaline alcoholic media to give 3-chloroindole. Iodometry was used to follow the rearrangement of N-chloroindole to 3-chloroindole. An induction period was observed prior to a pseudo-first-order process. The length of the induction period depended on the alcohol used and its proportion relative to n-hexane, the presence or absence of base, traces of water. Addition of water during the rearrangement caused an increase in the apparent concentration of N-chloroindole. This indicated the formation of another intermediate capable of reacting with water to either regenerate A′-chloroindole or form another species which can oxidize iodide ion. The anion of 3-chloroindole is proposed as the intermediate. In the absence of base the formation of a new intermediate which absorbed at 252 nm was observed. During its formation no change in the apparent concentration of N-chloroindole could be detected by iodometry. 3-Chloro-3H-indole is proposed as this new intermediate. Addition of base caused the rapid disappearance of this band. A mechanism is proposed in which the induction period is seen as the establishment of an equilibrium between N-chloroindole, 3-chloro-3.H-indole, the conjugate base of 3-chloroindole.