Catalytic Synthesis of Methacrolein via the Condensation of Formaldehyde and Propionaldehyde with L-Proline Intercalated Layered Double Hydroxides

Longxin Ju,Gang Li,Hongxian Luo

doi:10.3390/catal12010042

Longxin Ju, Gang Li + Show 1 more

Open Access

https://doi.org/10.3390/catal12010042

Copy DOI

Abstract

Aldol condensation reactions are very important C–C coupling reactions in organic chemistry. In this study, the catalytic performance of layered double hydroxides (LDHs) in the aldol condensation reaction of formaldehyde (FA) and propionaldehyde (PA) was investigated. The MxAl-LDHs (denoted as re-MxAl–LDHs; M = Ca and Mg; X = 2–4), as heterogeneous basic catalysts toward the aldol condensation reaction, were prepared via a two-step procedure. The catalyst exhibited a high PA conversion (82.59%), but the methacrolein (MAL) selectivity was only 36.01% due to the limitation of the alkali-catalyzed mechanism. On this basis, the direct intercalation of L-proline into LDHs also has been investigated. The influences of several operating conditions, including the temperature, reaction time, and substrate content, on the reaction results were systematically studied, and the optimized reaction conditions were obtained. The optimized Mg3Al–Pro-LDHs catalyst exhibited a much higher MAL selectivity than those of re-MgxAl–LDHs.

Highlights

Methacrolein (MAL) is an important chemical intermediate for the preparation of methyl methacrylate, thermoplastic monomers, and various fragrances and pharmaceuticals [1,2,3,4]
L-proline is introduced into different carriers, such as silica materials, metal-organic frameworks (MOFs) and layered double hydroxides (LDHs), and a good yield and a high enantioselectivity are obtained in an asymmetric aldol condensation [13,14,15]
Re-MxAl–LDHs were prepared by calcination and subsequently rehydration, and the X-ray Diffractometry (XRD) patterns are shown in Figures 1 and 2

Summary

Introduction

Methacrolein (MAL) is an important chemical intermediate for the preparation of methyl methacrylate, thermoplastic monomers, and various fragrances and pharmaceuticals [1,2,3,4]. Yu et al found that L-proline is the optimal catalyst for the Mannich synthesis of MAL among the various amino acid compounds, with a conversion of 97% and a yield of 94% [12]. The industrial application of this catalyst is challenged due to the cost and the subsequent separation To overcome this issue, L-proline is introduced into different carriers, such as silica materials, metal-organic frameworks (MOFs) and layered double hydroxides (LDHs), and a good yield and a high enantioselectivity are obtained in an asymmetric aldol condensation [13,14,15]. Active MxAl–LDHs catalysts with OH− interlayer anions (denoted as re-MxAl–LDHs; M = Ca and Mg; X = 2–4) were obtained and used in the aldol condensation reaction of FA with PA to produce MAL. The catalytic performances of these materials in aldol condensation were studied

Results and Discussion

Catalysts Preparation

Synthesis of MAL from FA and PA

Conclusions