Vapour-phase synthesis of 2-methyl- and 4-methylquinoline over BEA* zeolites

4-Methylquinoline and 2-methylquinoline were synthesized from acetaldehyde and aniline in the gas phase over BEA* zeolite catalysts. High combined yields of 2- and 4-methyl-substituted quinolines were obtained with H-BEA* zeolite and with BEA*-F synthesized in fluoride medium, with 4-methylquinoline being the predominant isomer. Postsynthesis fluorination of the H-BEA* with ammonium fluoride leads to dealumination and formation of extra-framework aluminium fluoride compounds. Product selectivities changed with time over this catalyst, such that 2-methylquinoline became the predominant product. New insight into the reaction mechanism is offered, and previous propositions can be rationalized based on these new results.