Halloysite Nanoclay with High Content of Sulfonic Acid-Based Ionic Liquid: A Novel Catalyst for the Synthesis of Tetrahydrobenzo[b]pyrans

Samahe Sadjadi,Neda Abedian-Dehaghani,Majid M. Heravi,Fatemeh Koohestani

doi:10.3390/catal11101172

Samahe Sadjadi, Neda Abedian-Dehaghani + Show 2 more

Open Access

https://doi.org/10.3390/catal11101172

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Abstract

One of the main drawbacks of supported ionic liquids is their low loading and consequently, low activity of the resultant catalysts. To furnish a solution to this issue, a novel heterocyclic ligand with multi imine sites was introduced on the surface of amino-functionalized halloysite support via successive reactions with 2,4,6-trichloro-1,3,5-triazine and 2-aminopyrimidine. Subsequently, the imine sites were transformed to sulfonic acid-based ionic liquids via reaction with 1,4-butanesultone. Using this strategy, high loading of ionic liquid was loaded on halloysite nanoclay. The supported ionic liquid was then characterized with XRD, SEM, TEM, EDS, FTIR, BET, TGA and elemental mapping analysis and utilized as a metal-free Brønsted acid catalyst for promoting one-pot reaction of aldehydes, dimedone and malononitrile to furnish tetrahydrobenzo[b]pyrans. The catalytic tests confirmed high performance of the catalyst. Moreover, the catalyst was stable upon recycling.

Highlights

Considering the importance of environmental concerns, development of green methodologies for the synthesis of chemicals has gained growing attention
Inthe thecontinuation continuation of of our our studies studies on on the the catalysts, catalysts, we
The nano tubes of halloysite nanoclay (Hal) can be discerned in the SEM images

Summary

Introduction

Considering the importance of environmental concerns, development of green methodologies for the synthesis of chemicals has gained growing attention In this regard, use of natural materials for the preparation of catalysts is a hot research topic [1,2,3,4,5]. Introduction of the functional groups on Hal improves its features as a supporting material and leads to the preparation of heterogeneous catalysts with improved activity and recyclability [42,43]. Proper functional group can be prepared separately and, immobilized on a support, In both methods, the loading of IL on the supporting materials is mostly low. At the end of the reaction, the precipitate was filtered off, washed with toluene and dried at 70 ◦ C in oven for 12 h, Figure 1

Methods

Discussion

Conclusion