Microwave Assisted Synthesis of Substituted Indoles Using Montmorillonite as Catalyst

摘要

A series of acid catalysts was prepared by heating NH_4-saturated montmorillonite at 200-600 ℃ for 24 h. Their catalytic activity was tested in microwave assisted Fischer indole synthesis. The most active catalyst was obtained after heating at 300 ?. It was only slightly less effective (84%) than the commercially available acid-activated montmorillonite K10 (90%). Acidity of the prepared materials was studied by infrared spectroscopy and thermal analysis of pyridine adsorbed on the catalysts. The IR spectra exhibit a peak near 1490 cm~(-1) corresponding to the catalytic activity. The DTG curves obtained for desorption of pyridine showed maxima near 50, 160, and 330 ℃. The intensity of the maximum near 160 ℃, attributed to pyridine desorption from Lewis acid sites, partially corresponded with the catalytic activity of the samples.