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首页> 外文期刊>Chemistry: A European journal >Schiff base structured acid-base cooperative dual sites in an ionic solid catalyst lead to efficient heterogeneous knoevenagel condensations
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Schiff base structured acid-base cooperative dual sites in an ionic solid catalyst lead to efficient heterogeneous knoevenagel condensations

机译：离子固体催化剂中的席夫碱结构化酸碱合作双位点可导致有效的异质Knoevenagel缩合

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摘要

An acid-base bifunctional ionic solid catalyst [PySaIm] _3PW was synthesized by the anion exchange of the ionic-liquid (IL) precursor 1-(2-salicylaldimine)pyridinium bromide ([PySaIm]Br) with the Keggin-structured sodium phosphotungstate (Na _3PW). The catalyst was characterized by FTIR, UV/Vis, XRD, SEM, Brunauer-Emmett-Teller (BET) theory, thermogravimetric analysis, 1H NMR spectroscopy, ESI-MS, elemental analysis, and melting points. Together with various counterparts, [PySaIm] _3PW was evaluated in Knoevenagel condensation under solvent and solvent-free conditions. The Schiff base structure attached to the IL cation of [PySaIm] _3PW involves acidic salicyl hydroxyl and basic imine, and provides a controlled nearby position for the acid-base dual sites. The high melting and insoluble properties of [PySaIm] _3PW are relative to the large volume and high valence of PW anions, as well as the intermolecular hydrogen-bonding networks among inorganic anions and IL cations. The ionic solid catalyst [PySaIm] _3PW leads to heterogeneous Knoevenagel condensations. In solvent-free condensation of benzaldehyde with ethyl cyanoacetate, it exhibits a conversion of 95.8 % and a selectivity of 100 %; the conversion is even much higher than that (78.2 %) with ethanol as a solvent. The solid catalyst has a convenient recoverability with only a slight decrease in conversion following subsequent recyclings. Furthermore, the new catalyst is highly applicable to many substrates of aromatic aldehydes with activated methylene compounds. On the basis of the characterization and reaction results, a unique acid-base cooperative mechanism within a Schiff base structure is proposed and discussed, which thoroughly explains not only the highly efficient catalytic performance of [PySaIm] _3PW, but also the lower activities of various control catalysts. Cooperative catalyst: The ionic solid prepared by pairing pyridine-based Schiff base tethered cations with phosphotungstate anions is proved to be a recoverable efficient heterogeneous catalyst for Knoevenagel condensations by means of the unique bulk-type acid-base cooperative mechanism (see scheme).
机译：通过将离子液体（IL）前体1-（2-水杨醛亚胺）溴化吡啶鎓（[PySaIm] Br）与Keggin结构磷钨酸钠（[PySaIm] Br）进行阴离子交换，合成了酸基双功能离子固体催化剂[PySaIm] _3PW Na _3PW）。通过FTIR，UV / Vis，XRD，SEM，Brunauer-Emmett-Teller（BET）理论，热重分析，1H NMR光谱，ESI-MS，元素分析和熔点对催化剂进行了表征。与各种对应物一起，在无溶剂和无溶剂条件下的Knoevenagel缩合反应中评估了[PySaIm] _3PW。附着在[PySaIm] _3PW的IL阳离子上的席夫碱结构涉及酸性水杨基羟基和碱性亚胺，并为酸碱双位点提供了受控的附近位置。 [PySaIm] _3PW的高熔融性和不溶性与PW阴离子的大体积和高价以及无机阴离子和IL阳离子之间的分子间氢键网络有关。离子型固体催化剂[PySaIm] _3PW导致非均相Knoevenagel缩合。苯甲醛与氰基乙酸乙酯的无溶剂缩合反应显示出95.8％的转化率和100％的选择性。转化率甚至远高于以乙醇为溶剂的转化率（78.2％）。固体催化剂具有便利的可回收性，在随后的再循环之后转化率仅略微降低。此外，这种新型催化剂非常适用于芳烃醛与活化亚甲基化合物的许多底物。在表征和反应结果的基础上，提出并讨论了席夫碱结构中独特的酸碱协同机理，不仅充分解释了[PySaIm] _3PW的高效催化性能，而且还解释了各种催化剂的低活性。控制催化剂。协同催化剂：通过独特的本体型酸碱协同机制，通过将吡啶基席夫碱系链阳离子与磷钨酸根阴离子配对制备的离子固体被证明是可回收的高效多相催化剂，用于Knoevenagel缩合反应。

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