The N-unsubstituted 4-aryl-1H-1,2,3-triazoles were synthesized via the acetic acid promoted cycloaddition between β-nitrostyrenes with sodium azide under transition-metal-free conditions in a continuous flow microreactor. The continuous-flow microreactor provided a safe environment for the dangerous reagents NaN3 and nitroalkene, and offered such a rapid procedure that the triazoles were formed in less than 4 min. In addition, the excess sodium azide was quenched by the by-product HNO2 in the presence of acetic acid. The scale-up experiment proved again that the yield did not drop in the flow reaction. Moreover, the synthesis of N-unsubstituted 1,2,3-triazole was also explored via a one pot reaction with aldehyde, nitromethane and sodium azide, and this reaction was monitored with an “in-tube retention time gradient” (IT-RTG) technology, which may be a novel application of the continuous-flow microreactor.Download high-res image (156KB)Download full-size image

•A novel catalyst for the reduction of nitroarenes to afford anilines.•Graphene supported bismuth iron oxide nanocomposite as the catalyst.•The catalyst is stable, chemically selective, and reusable.•The reaction under continuous flow is high efficient and safe.An efficient catalyst made of bismuth, iron and graphene oxide composite was developed for the reduction of nitroarenes with hydrazine hydrate to afford corresponding anilines. We found that the bismuth and graphene remarkably promoted the activity of iron oxide catalyst, so that a mixture of ferric chloride, bismuth nitrate and graphene oxide catalyzed the complete conversion of 4-nitrophenol into 4-aminophenol. Moreover, a catalyst prepared from the co-precipitation of bismuth, iron and graphene oxide nanocomposite (BFGO) exhibited perfect performance, and it could be recovered magnetically and reused for ten cycles without any activity losing. Furthermore, another heterogeneous catalyst tBFGO was constructed from the bismuth iron oxide nanocomposite with thermal exfoliated graphene. It was a robust and sustainable catalyst and was suitable to be used in the continuous flow microreactor. Applying a catalyst cartridge that filled up with tBFGO, a series of functionalized nitroarenes were successfully converted into corresponding anilines with excellent selectivity, and the work-up procedure was very easy. The catalytic activity of the catalyst did not decline within more than 600 min under a flow rate of 1 mL/min.Download high-res image (135KB)Download full-size image

A core–shell structured nanocatalyst (Fe3O4@SiO2-NH2-RhNPs@mSiO2) that is encapsulated with porous silica has been designed and prepared for catalyzing the transfer hydrogenation of nitro compounds into corresponding amines. Rh nanoparticles serve as the activity center, and the porous silica shell plays an important role in the “slow-release” of the hydrogen source hydrazine. This reaction can be carried out smoothly in the green solvent water, and the atom economy can be improved by decreasing the amount of hydrazine hydrate used to a stoichiometric 1.5 equivalent of the substrate. Significantly, high catalytic efficiency is obtained and the turnover frequency (TOF) can be up to 4373 h−1 in the reduction of p-nitrophenol (4-NP). A kinetics study shows that the order of reaction is ∼0.5 towards 4-NP, and the apparent active energy Ea is 58.18 kJ mol−1, which also gives evidence of the high catalytic efficiency. Additionally, the excellent stability of the catalyst has been verified after 15 cycles without any loss of catalytic activity, and it is easily recovered by a magnet after reaction due to the Fe3O4 nucleus.

A novel oCNT-Chitosan-xFe2O3⋅yBi2O3 nanocomposite has been synthesized as a catalyst for the reduction of nitroarenes to afford corresponding anilines. This catalyst exhibits excellent efficiency and high chemoselectivity towards varieties of nitro-compounds by using hydrazine hydrate as the reductant, and this magnetically separable nanocatalyst can be used for more than ten cycles. The synergy between iron and bismuth gives the catalyst competitive activity towards precious metallic catalyst, and the active sites are immobilized on the chitosan noncovalently functionalized oxidized carbon nanotubes gives the catalyst long life time. Furthermore, this heterogeneous catalyst was used in a continuous-flow processing by filling up it into a packed bed reactor. It was used for more than 1000 min without any loss of catalytic activity in a scaled-up reduction of p-nitrophenol with a productivity of 0.5mmol min−1.Download high-res image (204KB)Download full-size image

A microwave-assisted general method for the synthesis of 2-aminovinyl benzimidazoles has been developed. Treatment of the 1,2-phenylenediamines and N-arylated/N,N-dialkylated 3-aminoacroleins with bis(cyclopentadienyl)zirconium(IV) dichloride (Cp2ZrCl2) as the catalyst under microwave irradiation for 3–5 min followed by in situ MnO2 oxidation afforded thirteen 2-aminovinyl benzimidazoles in good yields.A microwave-assisted general method for the synthesis of a diversity of 2-aminovinyl benzimidazoles with Cp2ZrCl2 as the catalyst has been developed.

The cleavage of carboxylic acid esters is promoted by malachite in the presence of NaN3 under nearly neutral conditions. In methanol, the aliphatic alcohol esters are converted to methyl esters and corresponding alcohols in good to excellent yields, while the cleavage of phenolic esters gives phenols in quantitative yields. In most cases, the reaction conditions are quite mild so this methodology is efficient for the removal of the acyl-protecting group from the protected hydroxy functional groups. The possible catalytic mechanism is discussed according to some experimental features.