Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2-Propanol

Abstract

Here, we report transfer hydrogenation of nitroarenes to aminoarenes using 2-propanol as a hydrogen source and Ag-containing magnetically recoverable catalysts based on partially reduced graphene oxide (pRGO) sheets. X-ray diffraction and X-ray photoelectron spectroscopy data demonstrated that, during the one-pot catalyst synthesis, formation of magnetite nanoparticles (NPs) is accompanied by the reduction of graphene oxide (GO) to pRGO. The formation of Ag NPs on top of magnetite nanoparticles does not change the pRGO structure. At the same time, the catalyst structure is further modified during the transfer hydrogenation, leading to a noticeable increase of sp carbons. These carbons are responsible for the adsorption of substrate and intermediates, facilitating a hydrogen transfer from Ag NPs and creating synergy between the components of the catalyst. The nitroarenes with electron withdrawing and electron donating substituents allow for excellent yields of aniline derivatives with high regio and chemoselectivity, indicating that the reaction is not disfavored by these functionalities. The versatility of the catalyst synthetic protocol was demonstrated by a synthesis of an Ru-containing graphene derivative based catalyst, also allowing for efficient transfer hydrogenation. Easy magnetic separation and stable catalyst performance in the transfer hydrogenation make this catalyst promising for future applications.

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“…In this regard apart from H 2 ‐gas, isopropanol appeared as a suitable green solvent cum reducing agent for selective reduction of nitro‐arenes. Very recently Das et al . reported for the conversion of nitro‐arene to amine with a magnetically recoverable graphene based silver catalyst catalyst.…”

“…Similar amount of the Ar‐NO 2 , AuVNF, isopropanol and KOH initially mixed under magnetic stirring at room temperature was transferred to a Teflon lined autoclave and the tightly sealed autoclave was placed in an oven at 100 °C for 12 h. After 12 h of reaction, the product of Ar‐NH 2 was found to be 88% without any other minor products. The high product yield in autoclave condition might be due to the fast generation of insitu hydrogen from isopropanol …”

“…The catalytic reduction of Ar‐NO 2 are known to be influenced by various factors like temperature and catalyst . In order to investigate the influence of such parameters, the reaction was again performed at various temperatures varied from 40 °C to 140 °C (Figure S10a) keeping the catalyst amount to be 20 mg.…”

“…Like the OER and HER, the success in nitro‐arene reduction (NAR) reactions using isopropanol as internal reducing agent is very much limited . Till date only few catalytic systems are known to do the NAR at the expense of isopropanol oxidation . NAR reactions are commonly performed using reducing agents like sodium borohydride, hydrazine etc.…”

“…However, the presence of such reducing agents hampers the chemo‐selectivity of the product and also destroys the heterogeneity of the nanocatalyst . Nowadays, isopropanol is considered to be one of the alternate sources of hydrogen with no toxicity in NAR . Therefore, the catalyst that would do the NAR in isopropanol is highly demanding making the process to be much greener.…”