Synthesis, characterization, and application of silica supported ionic liquid as catalyst for reductive amination of cyclohexanone with formic acid and triethyl amine as hydrogen source

A silica supported ionic liquid was synthesized and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, X-ray diffraction, N2 adsorption-desorption, and thermogravimetric analysis. All these techniques, especially SEM results indicated the presence of well-defined spherical particles having diameters larger than the pristine silica particles, confirming the successful immobilization of the ionic liquid. The prepared silica supported ionic liquid was used in the reductive amination of cyclohexanone under different conditions with different azeotropic mixtures of formic acid and triethyl amine as a hydrogen source. The catalyst showed efficient catalytic performance and excellent yields of N-cyclohexyl amine derivatives in the range of 58% to 84% at 30 °C. After completion of the reaction, the catalyst was easily recovered by simple filtration and reused for another five cycles without any significant impact on product yields. The obtained catalytic performance indicates that the present catalyst is green, very active, and reusable for the reductive amination of cyclohexanone. A silica supported ionic liquid phase (SILP) was synthesized, and it showed excellent catalytic performance for the reductive amination of cyclohexanone. The catalytic activity of SILP is due to the synergistic effect of ILs and silica, the SILP activate the imine substrate to reduce by taking hydrogen from formic acid and triethyl amine which leads to amine product.