Polymer Encapsulated Cobalt‐Based Catalysts (Co EnCat^TM) for Selective Continuous Hydrogenation of 1‐Iodo‐4‐nitrobenzene

Abstract

New cobalt catalysts confined in an EnCatTM polyurea matrix by micro‐encapsulation of Al5Co2 or Al5Co2/Al3Ni2 phase containing alloys are disclosed for the reductive hydrogenation of 1‐iodo‐4‐nitrobenzene 1. The product 4‐iodo‐aniline 2 readily undergoes hydro‐desiodination and was used to demonstrate the extraordinary selectivity. Co EnCatTM significantly suppressed this follow‐up reaction under both batch and flow modes. The correlation between performance, elemental composition, and alloy content is presented for these novel catalysts. Among them, the hybrid micro‐encapsulated Co‐Ni catalyst showed higher activity than its Ni‐free analogue. In the flow process, this catalyst gave a high yield of 2 and very low level of 3. Hence, these novel Co EnCatTM catalysts hold promise with respect to the continuous‐flow hydrogenation of challenging halogenated nitroaromatic compounds.

Synthesis of flow‐compatible Ru-Me/Al2O3 catalysts and their application in hydrogenation of 1-iodo-4-nitrobenzene

“…The strong increase of the aniline yield shows that the hydro-dehalogenation reaction is more affected by temperature as the nitro group reduction. This observation was already reported for Co based catalyst [38,39]. Products formed by hydrogenation of the aromatic ring, observed previously at hydrogenation of nitrobenzene using a Ru/CNT catalyst [42], were also not detected.…”

“…The highest 4-iodoaniline yield in flow operation was obtained with the Ru-Sn/Al 2 O 3 and the yield increases within 6 h from 81 to 84 %. Assuming a 4-iodoaniline yield of 84 % the productivity of 4-iodaniline in the continuous process with the Ru-Sn/Al 2 O 3 catalyst amounted to 39.8 mmol• h − 1 •mmol Ru − 1 that is higher than that reported for Co-based catalysts [39]. The presence of the promotor had also an influence on the aniline yield.…”

“…However, both 1-iodo-4-nitrobenzene conversion as well as yield of 4-iodoaniline decreased with increasing operation time [36,39]. The deactivation of the Co based catalyst seems to be influenced from the substrate concentration [39] and was attributed at least partly to Co leaching from the catalyst surface [36].…”

“…Recently, different Co-based catalysts were developed and tested in the continuous process applying the above model reaction. These catalysts showed high yields above 90 % with high selectivity (90 %) towards the target product 4-iodoaniline and less than 2 % yield of the undesired side product aniline [25,36,39]. However, both 1-iodo-4-nitrobenzene conversion as well as yield of 4-iodoaniline decreased with increasing operation time [36,39].…”

“…These catalysts showed high yields above 90 % with high selectivity (90 %) towards the target product 4-iodoaniline and less than 2 % yield of the undesired side product aniline [25,36,39]. However, both 1-iodo-4-nitrobenzene conversion as well as yield of 4-iodoaniline decreased with increasing operation time [36,39]. The deactivation of the Co based catalyst seems to be influenced from the substrate concentration [39] and was attributed at least partly to Co leaching from the catalyst surface [36].…”