Studies on Deactivation of Iron Oxide Catalyst in Solvent-Free N-Benzylation of Aniline with Benzyl Chloride
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tudies on Deactivation of Iron Oxide Catalyst in Solvent-Free N-Benzylation of Aniline with Benzyl Chloride C. Dinga, H. Wanga, B. Lua, *, J. Zhaoa, and Q. Caia, ** a
School of Chemistry and Chemical Engineering, Harbin Normal University, Harbin, 150025 China *e-mail: [email protected] **e-mail: [email protected] Received February 8, 2020; revised February 27, 2020; accepted February 27, 2020
Abstract—Nano-α-Fe2O3 prepared using acid pickling waste as precursor was found to be an effective catalyst for benzylation aniline with benzyl chloride. However, the formation of a green solution was observed during the solvent-free benzylation. A yellow-green single crystal as a byproduct was recovered from the green reaction mixture and characterized by X-ray single crystal diffraction, 1H NMR, FT-IR and elemental analysis. The results showed that this single crystal was a composite structural complex constructed by [(C6H6– CH2)2NH–C6H6]FeCl4 and [(C6H6–CH2)2NH–C6H6]Cl in equimolar ratio. The formation of the complex led to the deactivation and non-reusability of α-Fe2O3 catalyst for catalyzing solvent-free N-benzylation of aniline with benzyl chloride. The forming mechanism of the crystal was also discussed. Keywords: nano iron oxide, N-benzylation, deactivation of catalyst, aniline DOI: 10.1134/S0023158420050031
INTRODUCTION Formation of C–N bond is one of the most important transformations in organic synthesis because amines are widely applied as intermediates for synthesis of fine chemicals, agrochemicals and pharmaceuticals [1]. Specifically, amines and amides include many drugs for treating various diseases [2]. N-alkylation of amine, as a typical strategy for C–N bond formation, was extensively applied for preparing secondary amines [3]. These processes utilize transition metals such as Ru complex [4], Pt–Sn/Al2O3 [5], Pd(OAc)2 [6], (Cp*IrCl2)2 (Cp* = pentamethylcyclopentadienyl) and Cu compounds as catalysts [7–11]. The copper compounds involving CuI, Cu2O and SiO2–Cu2O have received increasing attention due to their low cost and environment-benign character. Motivated by economic and ecological considerations, our group had developed much cheaper and environmentally friendly nano-α-Fe2O3 catalyst prepared from acid pickling waste, which was catalytically very active in benzylation of benzene, phenol and aniline or other amines with benzyl chloride [12, 13]. However, on monitoring the progress of solvent-free N-benzylation of aniline we observed that the color of solution containing the reaction mixture turned to green, indicating a possible side reaction. To clarify Abbreviations: DPA, N-dibenzyl phenyl aminium chloride.
this phenomenon, the products and byproducts encountered in the reaction mixture were separated and analyzed. As a result, a single crystal was recovered and its composition and structure was determined. The goal of the work reported here was to characterize deactivation of α-Fe2O3 and shed some light on the mechanism governing the generation of the crystal. EXPERIMENTAL Preparation and char
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