Selective monoallylation of anilines to N-allyl anilines using reusable zirconium dioxide supported tungsten oxide solid catalyst

Abstract

The monoallylation of aniline to give N-allyl aniline is a fundamental transformation process that results in various kinds of valuable building block allyl compounds, which can be used in the production of pharmaceuticals and electronic materials. For decades, sustainable syntheses have been gaining much attention, and the employment of allyl alcohol as an allyl source can follow the sustainability due to the formation of only water as a coproduct through dehydrative monoallylation. Although the use of homogeneous metal complex catalysts is a straightforward choice for the acceleration of dehydrative monoallylation, the use of soluble catalysts tends to contaminate products. We herein present a 10 wt% WO₃/ZrO₂ catalyzed monoallylation process of aniline to give N-allyl anilines in good yields with excellent selectivity, which enables the continuous selective flow syntheses of N-allyl aniline with 97–99% selectivity. The performed detailed study about the catalytic mechanism suggests that the dispersed WO₃ with the preservation of the W(VI) oxidation state of 10 wt% WO₃/ZrO₂ with appropriate acidity and basicity is crucial for the monoallylation. The inhibition of the over allylation of the N-allyl anilines is explained by the unwilling contact of the N-allyl aniline with the active sites of WO₃/ZrO₂ due to the steric hindrance.