Synthesis of 3-Methylindole from Glycerol Cyclization with Aniline over CuCr/Al₂O₃Catalysts Modified by Alkali Earth Oxides

Abstract

In the present work, CuCr catalysts supported on γ‐Al2O3 are prepared and modified with alkali earth elements by impregnation, characterized by N2 adsorption–desorption, XRD, H2‐TPR (temperature‐programmed reduction by H2), CO2‐TPD and NH3‐TPD (temperature‐programmed desorption of NH3 or CO2), and applied in the synthesis of 3‐methylindole (3‐MI) with a N‐heterocycle from glycerol and aniline in the fixed‐bed reactor. The results show that the introduction of alkali earth elements into the CuCr/Al2O3 catalyst can improve the yield of target 3‐MI in the order of Mg < Ca < Sr < Ba. CuCr‐Ba/Al2O3 gives rise to a high 3‐MI yield of 39.09% and 65.17% in N2 as a carrier gas and 20%H2–N2 mixture gas, respectively. According to catalysts characterization and catalytic tests, the reaction pathway of glycerol cyclization with aniline is proposed, the formation of 3‐MI and 3H‐indol‐3‐yl methanol is hypothesized to be through the aniline cyclization with 2,3‐hydroxypropanal from glycerol dehydrogenation over Cu0 centers and basic sites. The acidic sites mainly play a role on activating aniline, which interacts with glycerol to form 3‐MI or quinoline through cyclization and dehydration.

Catalytic cascade gas-phase heterocyclization of lactic acid and aniline into quinolones over mesoporous Hβ zeolite

“…Moreover, the produced 2-hydroxypropaldehyde can combine with aniline to form 3-methylindol, which then transforms into indol (ID) through dealkylation at high temperature. 66,67 Research has shown that the conversion of lactic acid leads to the production of 2,3-pentanedione and carbon dioxide, with the subsequent reaction of 2,3-pentanedione with aniline resulting in the formation of 2-methyl-3-ethylindol through addition and cyclization-aromatization processes. Additionally, the formation of coking in this reaction is attributed to the acid-induced polymerization of various active intermediates of acetaldehyde, acrolein, crotonaldehyde, etc.…”

Recent advances in the synthetic method and mechanism for the important N‐heterocyclic compound of 3‐methylindole

“…In addition, 3‐methylindole can be used in agriculture to synthesize plant growth regulators, herbicides, insecticides and so on [19]. Since the fragrance of the flower will be released after 3‐methylindole is diluted tens of thousands of times, it can be used to make essential oil blends and spices [20], and can also be used as food essences [21]. In recent years, chemists have also explored the other potency of 3‐methylindole such as synthesizing serotonin, activating the transcription of liver cytochrome P450 enzyme, which enriches the application of 3‐methylindole in the fields of biochemistry and genetics [22].…”

Catalytic transformations of glycerol via hydroxyacetone into nitrogen heterocycles of industrial interest

“…In the same way, a growing body of literature has recently started to examine the use of glycerol and glycerol derivatives as a carbon source to produce N-heterocycles. Some reports on pyridine synthesis that have been already mentioned [249][250][251][252], the oxazoline [279] and 3-methylindole [280] syntheses, processes to produce pyrazinyl compounds [281][282][283][284][285][286][287] [275,276].…”