Layered double hydroxide anchored ionic liquids as amphiphilic heterogeneous catalysts for the Knoevenagel condensation reaction

Abstract

In recent years, great attention has been dedicated to the development of heterogeneous base catalysts providing a green and sustainable process in benign aqueous media. Herein, the ionic liquid modified layered double hydroxide (LDH) based catalysts of LDH-IL-Cn (n = 4, 8, 12) were prepared by adopting an exfoliation/assembly strategy, in which the ionic liquids (ILs) were covalently anchored onto the surface of LDH layers. The resulting LDH-IL-Cn were characterized by FT-IR, solid-state ¹³C NMR, ²⁹Si CP/MAS NMR, ²⁷Al-MAS NMR, XRD, TG-DTA, BET, XPS, SEM, CO₂-TPD, contact angle experiments, etc. The catalytic performance of LDH-IL-C12 for the Knoevenagel condensation of a variety of aldehydes with ethyl cyanoacetate/malononitrile in H₂O at room temperature showed excellent yields and selectivities. Moreover, the base catalyst of LDH-IL-C12 can be easily recycled and reused for at least 5 times without the decrease of its catalytic efficiency. The scaled-up experiments revealed that the catalyst retained its efficiency and robustness.