The Catalytic Life of CdBr2–KBr and Its Affect on the Rate of Indole Formation from Aniline and Ethylene Glycol

In the liquid-phase synthesis of indole from aniline and ethylene glycol (EG), a CdBr2–KBr catalyst gave a high yield of indole. In recycling experiments using the catalyst in an autoclave, the yield of indole remained stable and the inorganic components of the catalysts did not suffer degeneration. The time course of the reaction under high pressure and high temperature was evaluated using a newly devised autoclave. The rate of formation of indole was determined to be proportional to the concentrations of both EG and the catalyst. Based on these findings for the reaction over CdBr2–3KBr, it is clear that this catalyst provides a simple and low-cost catalytic process for the formation of indole.