Cascade Aerobic Selective Oxidation over Contiguous Dual-Catalyst Beds in Continuous Flow
Cascade Aerobic Selective Oxidation over Contiguous Dual-Catalyst Beds in Continuous Flow
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DOI：
10.1021/acscatal.9b00092
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发表时间：
2019-06-01
期刊：
影响因子：
12.9
通讯作者：
Lee, Adam F.
中科院分区：
文献类型：
--
作者：
Durndell, Lee J.;Isaacs, Mark A.;Lee, Adam F.
级联反应代表了一种原子经济和能源效率高的技术，通过该技术可以减少化学制造所需的操作次数。生物催化级联在自然界中普遍存在，然而，控制反应物、中间体和活性位点之间的相互作用顺序仍然是化学催化的挑战。在这里，我们展示了一种方法来实现高效的级联，通过流动化学使用化学催化剂。在连续流动操作下，双床配置中的Pd/SBA-15和Pt/SBA-15非均相催化剂的紧密偶联提供了84%的高单程产率（比间歇操作提高了20倍）和高稳定性（肉桂醇级联氧化中>14000次周转）为肉桂酸，尽管两种催化剂单独对该反应均无活性。Pd（第一床）和Pt（第二床）催化剂的合理排序对于促进级联氧化相对于不期望的氢化和氢解是关键的，后者优于反向床序列或单个混合PdPt反应器床。在最佳双床配置中保留了每个床的固有催化性能，从而能够定量预测其单独氧化行为已建立的反应物/中间体的最终产物产率。使用连续反应器床的连续处理使得使用“简单”催化剂的级联的即插即用设计成为可能。
Cascade reactions represent an atom-economical and energy-efficient technology by which to reduce the number of manipulations required for chemical manufacturing. Biocatalytic cascades are ubiquitous in nature; however, controlling the sequence of interactions between reactant, intermediate(s), and active sites remains a challenge for chemocatalysis. Here, we demonstrate an approach to achieve efficient cascades using chemical catalysts through flow chemistry. Close-coupling of Pd/SBA-15 and Pt/SBA-15 heterogeneous catalysts in a dual bed configuration under continuous flow operation affords a high single pass yield of 84% (a 20-fold enhancement over batch operation) and high stability for >14000 turnovers in the cascade oxidation of cinnamyl alcohol to cinnamic acid, despite both catalysts being individually inactive for this reaction. Judicious ordering of Pd (first bed) and Pt (second bed) catalysts is critical to promote cascade oxidation with respect to undesired hydrogenation and hydrogenolysis, the latter favored over the reverse-bed sequence or a single mixed PdPt reactor bed. The intrinsic catalytic performance of each bed is preserved in the optimal dual-bed configuration, enabling quantitative prediction of final product yields for reactants/intermediates whose individual oxidation behavior is established. Continuous processing using contiguous reactor beds enables plug-and-play design of cascades employing "simple" catalysts.