Highly selective synthesis of 2,6-bis(4-methylphenyl)pyridine over novel mesoporous solid acid catalysts

Abstract

Aminocyclization reaction of 4-methyl acetophenone (4-MAP) with formaldehyde and ammonia was contacted under vapor phase reaction conditions over novel mesoporous Zn–Al–MCM-41 catalysts with different Si/(Zn + Al) ratios for highly selective synthesis of 2,6-BP (2,6-bis(4-methylphenyl)pyridine). For the reactions, the influences of various reaction parameters such as different catalysts, reaction temperature, reactant molar ratio, WHSV, TOS and recyclability are discussed. With increasing the Si/(Zn + Al) ratios of Zn–Al–MCM-41 catalysts from 75 to 380, the conversion of 4-methyl acetophenone (4-MAP), and the yield and selectivity of 2,6-BP decreased because the number of Brønsted acid sites in Zn–Al–MCM-41 catalysts is found to decrease almost linearly with increasing ratios of Si/(Zn + Al). Further the catalytic results were compared with those obtained by using Al–MCM-41, HY, Hβ, HM and H-ZSM-5 zeolites. The conversion and selectivity is increased in Zn–Al–MCM-41(21) with each cycling of reaction because its catalytic activity does not change. The Si/(Zn + Al) ratio of 21 is found to be more suitable for the aminocyclization reaction of 4-MAP to highly selective synthesis of 2,6-BP. Thus the selectivity of 2,6-BP is higher in Zn–Al–MCM-41(21) than that in other Zn–Al–MCM-41, Al–MCM-41, HY, Hβ, HM and H-ZSM-5.