Environmentally Benign Synthesis Using Nanostructure-Controlled Base Catalysts

碱性有机基团固定硅酸盐材料已被用作多相催化剂，用于C-C键的形成反应，如Knovenagel缩合、Aldol缩合和Michael加成。当使用胺负载的介孔二氧化硅作为碱催化剂时，胺位和二氧化硅载体的真实效果还没有得到很好的研究。在这里，我们考察了胺本身对反应的影响，以及硅酸盐添加剂如SBA-15和其他有序多孔硅酸盐的共轭效应。结果表明，仲胺(作为碱)和周期性介孔硅酸盐(作为添加剂)的组合大大提高了芳香醛与丙酮反应的活性，从而选择性地生成了β-羟基酮。在没有介孔硅酸盐的情况下，产率很低，而且介孔二氧化硅本身是完全惰性的。结果表明，硅酸盐的显著作用不仅是由于硅酸盐表面反应物浓度的增加，而且是由于碱与酸的协同作用。胺固定硅酸盐(有机官能化分子筛，OFMS)的活性高于胺和硅酸盐的简单混合物。通常情况下，当载体为有序介孔材料且反应在极性溶剂中进行时，OFMS是有效的，但在非极性溶剂中产率较低。相比之下，硅酸盐-有机复合材料(SOCM)在非极性溶剂中表现出显著的活性。介孔硅酸盐比微孔硅酸盐具有更高的活性。认为SOCM催化剂的活性中心是位于孔内靠近孔口的SiO_2~-(^+Nr_4)部分。虽然高活性不是由于浸出的物种，但在重复使用后观察到活性逐渐丧失。

Basic organic group-immobilized silicate materials have been utilized as the heterogeneous catalysts for C-C bond formation reactions such as Knoevenagel condensation, aldol condensation, and Michael addition. When using the amine-immobilized mesoporous silicas as base catalysts, the real effects of amine site and silica support have not been well investigated. Here we examined the effect of amine itself on the reaction as well as the conjugate effect of silicate additives such as SBA-15, and other ordered porous silicates. As a result, the combination of some secondary amine (as a base) and periodical mesoporous silicate (as an additive) drastically enhanced the reactivity in the reaction of aromatic aldehydes with acetone leading to the selective formation of β-hydroxyketones. The yield was low in the absence of the mesoporous silicate and the mesoposous silica itself was totally inert. It was suggested that the prominent effect of the silicate is not only due to the increase in the reactant concentration on the silicate surface but also to synergistic effect of base with acid. Activity of amine-immobilized silicate (organic-functionalized molecular sieves ; OFMSs) is higher than that of the simple mixture of amine and silicate. Very often, the OFMSs were effective when the supports were ordered mesoporous material and the reaction was carried out in polar solvents ; however, the yield was low in a non-polar solvent. In contrast, silicate-organic composite materials (SOCMs) were remarkably active in a non-polar solvent. The mesoporous silicate was more active than the microporous silicate. The active sites of the SOCM catalysts were considered to be SiO^-(^+NR_4) moieties located inside the pore near the pore-entrance. Although the high activity was not due to the leached species, a gradual loss of activity was observed after repeated use.