Visible‐Light‐Driven Chemoselective Hydrogenation of Nitroarenes to Anilines in Water through Graphitic Carbon Nitride Metal‐Free Photocatalysis

Abstract

Green and efficient procedures are essential for the chemoselective hydrogenation of functionalized nitroarenes to form industrially important anilines. Herein, it is shown that visible-light-driven, chemoselective hydrogenation of functionalized nitroarenes with groups sensitive to forming anilines can be achieved in good to excellent yields (82-100 %) in water under relatively mild conditions and catalyzed by low-cost and recyclable graphitic carbon nitride. The process is also applicable to gram-scale reaction, with a yield of aniline of 86 %. A study of the mechanism reveals that visible-light-induced electrons are responsible for the hydrogenation reactions, and thermal energy can also promote the photocatalytic activity. A study of the kinetics shows that this reaction possibly occurs through one-step hydrogenation or stepwise condensation routes. A wide range of applications can be expected for this green, efficient, and highly selective photocatalysis system in reduction reactions for the synthesis of fine chemicals.

Rational design of hydrogenation catalysts using nitrogen-doped porous carbon

“…However, the performance of this catalyst was relatively poor at low temperatures. Xiao et al [33] used low-cost graphitic C3N4 (g-C3N4) as a metal-free catalyst for the chemoselective hydrogenation of different functionalized nitroarenes at 70-90 °C, with good yields (>82%) in water under visible light. Moreover, this catalyst could be reused multiple times and applied in a gram-scale reaction (86% yield of aniline).…”

Visible‐Light Driven Ni‐Incorporated CdS Photocatalytic Activities for Azo‐Bond Cleavages with Hydrogenation Reaction

“…Other synthesis procedures of aniline from NB can also be done at 90–125 °C under high pressure of hydrogen [10] or H 2 pressure at 3 MPa in ionic liquid [11] or at room temperature with electrocatalysis [12] . On the other way, NB also can be chemically converted to aniline over Bi 2 MoO 6 with ammonium oxalate as a reducing agent or over g‐C 3 N 4 with hydrazine in 80 °C water [11,13] . Furthermore, the 4‐NP‐to‐4‐AP conversion in a mild condition also needs a strong reducing agent to provide hydrogen ions.…”

“…[12] On the other way, NB also can be chemically converted to aniline over Bi 2 MoO 6 with ammonium oxalate as a reducing agent or over g-C 3 N 4 with hydrazine in 80°C water. [11,13] Furthermore, the 4-NP-to-4-AP conversion in a mild condition also needs a strong reducing agent to provide hydrogen ions.…”

Ag/Ag2O confined visible-light driven catalyst for highly efficient selective hydrogenation of nitroarenes in pure water medium at room temperature

“…[14,15,17,[20][21][22][23][24]. Although a couple of works tried to use aqueous systems to hydrogenate nitroarenes, their atomic hydrogen was produced mainly based on the reaction between metal [18] or NaBH 4 [25] with water rather than photoinduced atomic hydrogen, leading to a relatively low conversion [18,25,26], as a result, high reaction temperature combined with long reaction time were used to boost the photocatalytic process [26]. Therefore, how to enhance the diffusion-and hydrogen transfer-independent photocatalytic reaction remains a big challenge for the hydrogenation of nitroarenes in pure water medium at room temperature.…”

“…Herein, we report a novel visible-light driven photocatalyst by introducing the nanospace of double-shelled hollow silica spheres as a photocatalytic nanoreactor for the first time, in which the confined Ag/Ag 2 O nanoparticles (metal-semiconductor) are easy to be excited and generate lots of electron/hole pairs under visible-light irradiation for quick hydrogenation reaction even in pure aqueous media because photoinduced atomic hydrogen can rapidly be transferred to nitroarenes in the confined nanospace [14,15,17,18,[20][21][22][23][24]26]. Although confined concept has been widely used for designing common catalysts, it has never been used for light-driven catalysts owing to the optical opacity of supports (Figure S1).…”