Sulfonic acid functionalized metal-organic framework (S-IRMOF-3): a novel catalyst for sustainable approach towards the synthesis of acrylonitriles

Abstract

A sulfonic acid functionalized metal-organic framework (S-IRMOF-3) has been synthesized by dropwise addition of chlorosulfonic acid (0.5 mL) in IRMOF-3 (1 g) containing 20 mL of CHCl₃ at 0 °C under simple stirring. The catalyst was applied in Knoevenagel condensation of various aromatic and hetero-aromatic aldehydes forming acrylonitrile derivatives. The catalyst was characterized thoroughly by using FT-IR, XRD, ¹³C MAS NMR, SEM, EDX, elemental mapping, TEM, BET, NH₃-TPD and TGA/DTA techniques. The presence of characteristic bands at 1694 cm^-1, 1254-769 cm^-1 and 1033 cm^-1 in the FT-IR spectrum, 2θ ≃ 6.7° and 9.8° in the XRD pattern and δ = 31.79, 39.55, 129.61, 131.46 (4C, CH), 133.54, 140.07 (2C), 167.71, 171.47 ppm (2C, 2C[double bond, length as m-dash]O) in the solid state ¹³C MAS NMR spectrum confirmed the successful formation of catalyst. This new eco-friendly approach resulted in a significant improvement in the synthetic efficiency (90-96% yield), high product purity, and minimizing the production of chemical wastes without using highly toxic reagents for the synthesis of acrylonitriles with selectivity for (Z)-isomer. Steric interactions seem to have an influence on the control of the Z-configurational isomers. By performing DFT calculations, it was found that the (Z)-isomer 3a is stabilized by 1.64 kcal mol^-1 more than the (E)-isomer. The catalyst could be reused for five consecutive cycles without substantial loss in catalytic activity.

Scheme 1

Fig. 1. The infrared spectra of IRMOF-3, S-IRMOF-3 and recycled S-IRMOF-3.

Fig. 2. XRD patterns of (a) IRMOF-3, (b) S-IRMOF-3 and (c) recycled S-IRMOF-3.

Fig. 3. Solid state ¹³C MAS NMR spectrum of S-IRMOF-3.

Fig. 4. SEM images of (a) IRMOF-3 and (b) the synthesized catalyst (S-IRMOF-3) at different magnifications.

Fig. 5. (a) EDX analysis of S-IRMOF-3. (b) Elemental mapping of S-IRMOF-3.

Fig. 6. TEM images of fresh catalyst (A) and recycled catalyst (B).

Fig. 7. TG/DT analysis of the catalyst.

Fig. 8. Effect of SO₃H content on thermal stability of catalyst.

Fig. 9. N₂ adsorption isotherms of (a) IRMOF-3 and (b) S-IRMOF-3. PSD of (c) IRMOF-3 and (d) S-IRMOF-3.

Fig. 10. NH₃-TPD curves of (a) IRMOF-3 and (b) S-IRMOF-3.

Scheme 2. General scheme for the formation of acrylonitrile derivatives.

Scheme 3. Proposed reaction mechanism.

Fig. 11. Recycling data of S-IRMOF-3 catalyst.

Fig. 12. Ground state optimized structures of the (a) (Z)-isomer and (b) (E)-isomer of compound 3a.

Fig. 13. Theoretically obtained infrared (IR) spectrum of the (Z)-isomer by DFT calculations.

Fig. 14. Electron density distributions in the (a) HOMO and (b) LUMO of the (Z)-isomer.