Synthesis of 2,2,4-trimethyl-1,2-dihydroquinolines over metal-modified 12-tungstophosphoric acid-supported gamma-Al(2)O(3)catalyst

摘要

In spite of having significant pharmacological importance, scalable synthesis of 2,2,4-trimethyl-1,2-H-dihydroquinoline (TMQ) is always being cumbersome due to harmful solvents, drastic reaction conditions, and high recovery cost of homogeneous catalysts. Heterogeneous catalytic condensation of aniline with acetone was employed here to synthesize TMQ. As efficient materials, Zn2+-, Sn2+-, and Cu2+-exchanged tungstophosphoric acid (TPA) supported on gamma-Al(2)O(3)was synthesized by microwave-assisted hydrothermal method. The synthesized catalysts were thoroughly characterized by XRD, Raman, FE-SEM, etc. and were screened for condensation reaction. Among the metal-exchanged catalysts, Zn(0.5)TPA/Al(2)O(3)showed highest aniline conversion with the highest yield of TMQ up to three consecutive cycles. The acidic sites over the catalysts were probed by pyridine-adsorbed FT-IR spectra and NH3-TPD studies. The reaction conditions were optimized, and plausible reaction mechanistic pathway was derived from FT-IR and GC-MS data.