Synthesis of indoles by dehydrodehydration and dehydration of aniline and ethylene glycol over Pt-based alumina catalysts

This paper report a cost-effective, green, and acceptorless dehydrogenative one-pot synthesis of indole derivatives from ethylene glycol and aniline derivatives using an acidic alumina-supported Pt nanoparticle catalyst (Pt/Al2O3) with 3 wt% Pt loading. The indole yield could reach more than 50%, which was further expanded to synthesize eight indole derivatives including 5-methoxyindole. Catalyst characterisation showed that Pt/Al2O3 was weakly acidic catalyst, the Pt particles were highly dispersed in nano-size on the surface of the Al2O3. The mechanistic studies shows that the indoles proceeded via successive dehydrogenation, condensation and dehydration steps with high showed atomic efficiency, with N-(2-Hydroxyethyl) aniline as the key intermediate, and N,N'-diphenylethylenediamine and 1,4-diphenylpiperazine as the main by-products.