Nitrogen and oxygen-doped metal-free carbon catalysts for chemoselective transfer hydrogenation of nitrobenzene, styrene, and 3-nitrostyrene with hydrazine

Abstract

An activated carbon (AC) was treated by hydrogen peroxide and ammonia to dope oxygen and nitrogen on its surface. The surface-functionalized AC catalysts were used for the transfer reduction of nitrobenzene, styrene, and 3-nitrostyrene by hydrazine hydrate. The reduction of nitrobenzene and 3-nitrostyrene was promoted over the oxygen-and nitrogen-doped catalysts compared to the parent AC catalyst. Those were less active for the reduction of styrene but active for the reduction of vinyl group of 3-nitrostyrene. However, the nitrogen dopant suppressed the reduction of vinyl group of 3-vinylaniline. The functionalized AC catalysts are likely to facilitate the adsorption and activation of nitro group of the nitro substrates through interactions with polarized surface induced by the oxygen and nitrogen hetero dopants. This should make it possible to reduce the vinyl group of 3-nitrostyrene on the surface. The nitrogen dopant hindered the reduction of the vinyl group of 3-vinylaniline because the adsorption through its amino group should become difficult on the surface of basic nature induced by the nitrogen doping. The AC serves as an electrical conductor and its performance should be enhanced by the surface functionalization and this would contribute to the formation of reducing species such as diimide and proton from hydrazine on the surface.The present results show that oxygen-and/or nitrogen-doped, functionalized carbon materials could be promising as metal-free multi-task catalysts.

Nitrogen-Doped Activated Carbon as Metal-Free Catalysts Having Various Functions

“…These results imply that both surface oxygen and nitrogen species contribute to the formation of active sites. Actually, the NB conversion increased linearly with the total amount of surface oxygen and nitrogen species [14]. Probably, those sites would activate both or either of hydrazine and NB molecules, as illustrated in Scheme 8 [14].…”

“…The selectivity of the hydrogenation of nitro or alkene groups can be tunable by selecting the reducing reagent. Under these circumstances, our group employed N-AC and N-OAC for the hydrogenation of nitrobenzene (NB), styrene (ST), and 3-nitrostyrene (NS) with hydrazine (Scheme 7a-c) [14]. …”

“…Actually, the NB conversion increased linearly with the total amount of surface oxygen and nitrogen species [14]. Probably, those sites would activate both or either of hydrazine and NB molecules, as illustrated in Scheme 8 [14]. For comparison, one selected N-AC was employed for the NB hydrogenation using gaseous hydrogen at 2 MPa.…”

“…The present authors doped nitrogen to an activated carbon (AC) by treating in a mixture of ammonia and air at temperatures of 400-800 °C. The nitrogen-doped AC (N-AC) materials, so prepared, are active for such several liquid phase reactions as Knoevenagel condensation [11], transesterification [11], aerobic oxidation of xanthene [12] and alcohols [13], and chemo-selective reduction of nitrobenzene, styrene, 3-nitrostyrene, and phenylacetylene with hydrazine [14,15], which are ordinarily catalyzed by bases, metals, and metal oxides [16][17][18][19][20][21][22]. X-ray photoelectron spectroscopy (XPS) surface analysis indicates that different types of nitrogen dopants are involved in the formation of catalytically active sites for those different reactions.…”

Preparation of FeO(OH) Modified with Polyethylene Glycol and Its Catalytic Activity on the Reduction of Nitrobenzene with Hydrazine Hydrate

“…Among the hydrogen donors, hydrazine hydrate is a suitable alternative for CTH due to its high activity and low cost. The reduction of nitroarenes with hydrazine hydrate could be catalyzed by a variety of cata-lysts such as Pd [5], Rh [6], Raney Ni [7], actived carbon [8,9], Fe3O4 [10,11] and iron(III) compounds [12], etc. The iron-based compounds are generally cheaper, but their catalytic properties are not desirable.…”