Specific lift-up behaviour of acetate-intercalated layered yttrium hydroxide interlayer in water: application for heterogeneous Br?nsted base catalysts toward Knoevenagel reactions?

Catalysis Science & Technology Pub Date: 2022-01-31 DOI: 10.1039/D1CY02328D

Abstract

Various alkylcarboxylate-intercalated layered yttrium hydroxides (Cn?1H2n?1COO?/Y-layered rare-earth hydroxide (LRH), n = 1–10) were synthesised by a simple anion exchange method using Cl?/Y-LRH as a parent material. The anion exchange from Cl? into CH3COO? proceeded rapidly, as confirmed by the time-resolved synchrotron-radiation X-ray diffraction (t-SXRD) analysis. The interlayer distance of Cn?1H2n?1COO?/Y-LRH could be controlled precisely, and the basal spacings calculated from XRD were linearly proportional to the length of alkyl groups. In water solvent, the basal spacing of the CH3COO?/Y-LRH catalyst based on the (00l) plane increased from 1.00 nm under dry conditions to 1.35 nm, and this lifted-up layered structure was generated immediately. By use of the CH3COO?/Y-LRH catalyst, a wide range of substrates were converted into the corresponding α,β-unsaturated nitriles in water via Knoevenagel condensation. Our synthesised heterogeneous catalyst acted as a Br?nsted base for this organic transformation, and it was reusable without any loss of its catalytic activity and selectivity.

Graphical abstract: Specific lift-up behaviour of acetate-intercalated layered yttrium hydroxide interlayer in water: application for heterogeneous Br?nsted base catalysts toward Knoevenagel reactions
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