An Insight into the Application of Alkali Metal Nitrate Impregnated β-Tricalcium Phosphate in the Hydration of Aromatic Nitriles
Yuvaraj Gangarajula, Buvaneswari GopalIntroduction:
Nitrile hydration reaction is considered one of the highly atom-economical and prominent green chemistry approaches for the synthesis of amides under aqueous medium.
materials and methods:
Materials and Methods Material Ammonium dihydrogen phosphate (S.d. fine chemicals), Calcium Carbonate (99+%, Sigma Aldrich), Nitric Acid (69-72%, S.d. fine chemicals), Urea (99%, S.d. fine chemicals), Lithium nitrate (99%, SRL Chemicals), Sodium nitrate (98%, Qualigens), Potassium nitrate (99%, S.d. fine chemicals). Preparation of β – Tricalcium phosphate by combustion method Appropriate weight of CaCO3 (2.0018g) and ammonium di hydrogen phosphate (NH4H2PO4, 3.45 g) was separately dissolved in 20 mL of 2M nitric acid and 25 mL of distilled water respectively. To the obtained Ca(NO3)2 solution and prepared NH4H2PO4 solution were mixed slowly and stirred. To the above solution mixture, 1.6016 g of urea was added and stirred until the solution becomes homogeneous. The furnace was heated to 500 °C prior to placing the sample for 15 min at 500 °C. The solid obtained was ground and calcined at two different temperatures (600 °C for 1h and 900 °C for 3 h). Preparation of Li/β-TCP by impregnation method Appropriate amount of lithium nitrate was added into 25 mL of distilled water and stirred for 5min to get homogeneous solution. To the above solution, as-prepared β-TCP powder was added with weight ratio of 1: 2 (TCP: LiNO3) and stirred for 1h and evaporated to dryness. The collected sample was subjected to heat treatment at 900 °C for 2 h. Similarly, K/β-TCP, Na /β-TCP and Li/HAP catalysts were also prepared by the procedure mentioned above. Catalytic Test The activity of as-prepared catalysts was screened in hydration of nitrile under reflux condition. To the benzonitrile (2.5 mmol), Li/β-TCP catalyst (0.1g) and water (7.5 mL) was added and refluxed under stirring condition (~550–600 rpm) at 125 °C for 3 h and cooldown to room temperature. After the reaction, ethanol was added and then, the catalyst was separated by filtration. The filtrate was placed on water bath to evaporate the solvent. The collected mass was purified using column chromatography with petroleum ether: ethyl acetate mixture as eluent. Melting point, FT-IR and 1H NMR spectrum was used to confirm the amide formation, and their corresponding data has been given in the supporting information. Characterization The structural information of as-prepared supports and catalysts was confirmed by powder X-ray diffraction (Cu Kα, Bruker, D8 Advanced) and Fourier transform infrared spectroscopy (JASCO FT-IR-4100 spectrometer). The amide formation was confirmed by their melting points, 1HNMR, (Bruker AVANCE III 400 MHz) and Fourier transform infrared spectroscopy (JASCO FT-IR-4100 spectrometer).
Methods:
Alkali metal nitrates (LiNO3, NaNO3, and KNO3) modified β-TCP were prepared by the impregnation method, and the catalytic activity of the prepared catalysts was screened in the nitrile hydration reaction.
Results:
Selective conversion of aromatic and heteroaromatic nitriles to respective amides has been achieved with alkali metal nitrate modified β-TCP catalysts under reflux conditions. Among the cat-alysts tested, LiNO3 impregnated β-TCP (Li/β-TCP) exhibits superior activity, whereas NaNO3 im-pregnated β-TCP (Na/β-TCP) and KNO3 impregnated β-TCP (K/β-TCP) catalysts exhibit relatively lower activity.
Discussion:
FT-IR and powder XRD analysis of Li/β-TCP confirmed the generation of CaO species as a new phase during the nitrate decomposition process, whereas CaO species were absent on both Na/β-TCP and K/β-TCP catalysts.
Conclusion:
The present study demonstrates that in situ generated CaO species on Li/β-TCP catalyst are responsible for its higher activity in thnitrile hydration reaction.