Abstract
Background: Nickel-Boron amorphous alloys (catalysts) of various Ni:B ratio were synthesized and well characterized using XRD, ICP-AES, EDAX and IR spectroscopic technique. Among all the catalysts, Ni:B alloy catalyst with ratio 1:1 was found to effective for catalytic transfer hydrogenation reaction using hydrazine hydrate as a proton donor. The present work shows the effect of metalloid content and the presence of aniline over CTH of nitrobenzene. The present catalytic protocol was found effective for wide variety of substrates showing its efficacy.
Methods: A typical catalytic transfer hydrogenation reaction of nitroaromatics using hydrazine hydrate was carried out in 2 necked, 25 ml round bottom flask in methanol. The progress of the reaction was monitored by the gas chromatography and products were further confirmed by GC-MS analysis. Nickel-Boron amorphous alloys (catalysts) were well characterized by XRD, SEM, EDX and ICP-AES analysis.
Results: Among various compositions of Ni:B alloy catalysts, 1:1 ratio was found optimum for the CTH of nitrobenzene. It was observed that with increase in amount of nickel, catalytic activity for CTH decreases. Effect of aniline on reaction was evaluated by concentration versus time plot. Considerable induction period was observed in absence of aniline not in case of other bases like NaOH, KOH, Na2CO3, etc confirming role of aniline in CTH reaction. From the Arrhenius plot for the CTH of nitrobenzene, the Ea was found to be 23.636 KJ mol-1. The catalytic protocol was found robust and effective for various substituted nitroaromat.ics.
Conclusion: Among various compositions obtained from ICP-AES analysis, the Ni:B alloy i.e. Ni62.71 B37.29 found to be the most efficient catalyst for the CTH of nitroaromatics over the other compositions. The catalyst found robust without changing its surface morphology after the reaction confirmed by SEM. Compared to reported catalytic system; this catalytic system is highly active and even worked with very low catalyst loading of 1 wt%. Apart from it we observed induction period for the said reaction and found that the presence of aniline hastens the rate of reaction. The system was widely applicable for the variety of substituted nitroaromatics which makes the system more interesting.
Keywords: Nickel-boron amorphous alloy, Amorphous catalysis, catalytic transfer hydrogenation, Heterogeneous catalysis.
Graphical Abstract
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