Chitosan as a Sustainable Organocatalyst: A Concise Overview
Chitosan as a Sustainable Organocatalyst: A Concise Overview
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DOI：
10.1002/cssc.201402718
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发表时间：
2015-01-01
期刊：
影响因子：
8.4
通讯作者：
El Kadib, Abdelkrim
中科院分区：
文献类型：
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作者：
El Kadib, Abdelkrim
对更可持续的材料和化学工艺的需求增加，极大地促进了多糖的使用，多糖是天然生物聚合物，在吸附，催化等领域，并作为替代化学原料。在这些生物聚合物中，通过天然甲壳质脱乙酰化获得的壳聚糖的使用正在增加，这是由于聚合物主链上存在氨基，使其成为天然阳离子聚合物。基于壳聚糖的材料形成具有可接近的碱性表面位点的开放网络、大孔、高表面积水凝胶的能力使得它们不仅能够用作活性金属催化剂的大螯合配体和作为分散纳米尺寸颗粒的载体，而且还能够用作直接有机催化剂。本文综述了天然和改性壳聚糖作为有机催化剂的应用，具有不同的质地和化学性质。利用壳聚糖的有机催化主要集中在碳-碳键形成反应、多组分杂环形成反应、生物柴油生产和通过[3+2]环加成固定二氧化碳。此外，壳聚糖骨架的手性螺旋结构使其本身可用于对映选择性催化。壳聚糖衍生物通常显示出与均相碱、离子液体以及有机和无机盐类似的反应性。然而，在活性位点处引入协同酸碱相互作用实质上增强了反应性。这些功能性生物聚合物也可以很容易地回收，并在无溶剂条件下重复使用多次。这些成就突出了天然生物聚合物在促进可持续化学方面的重要作用。
Increased demand for more sustainable materials and chemical processes has tremendously advanced the use of polysaccharides, which are natural biopolymers, in domains such as adsorption, catalysis, and as an alternative chemical feedstock. Among these biopolymers, the use of chitosan, which is obtained by deacetylation of natural chitin, is on the increase due to the presence of amino groups on the polymer backbone that makes it a natural cationic polymer. The ability of chitosan-based materials to form open-network, macroporous, high-surface-area hydrogels with accessible basic surface sites has enabled their use not only as macrochelating ligands for active metal catalysts and as a support to disperse nanosized particles, but also as a direct organocatalyst. This review provides a concise overview of the use of native and modified chitosan, possessing different textural properties and chemical properties, as organocatalysts. Organocatalysis with chitosan is primarily focused on carbon-carbon bond-forming reactions, multicomponent heterocycle formation reactions, biodiesel production, and carbon dioxide fixation through [3+2] cyclo-addition. Furthermore, the chiral, helical organization of the chitosan skeleton lends itself to use in enantioselective catalysis. Chitosan derivatives generally display reactivity similar to homogeneous bases, ionic liquids, and organic and inorganic salts. However, the introduction of cooperative acid-base interactions at active sites substantially enhances reactivity. These functional biopolymers can also be easily recovered and reused several times under solvent-free conditions. These accomplishments highlight the important role that natural biopolymers play in furthering more sustainable chemistry.