Recyclability of water-soluble ruthenium–phosphine complex catalysts in multiphase selective hydrogenation of cinnamaldehyde using toluene and pressurized carbon dioxide
Recyclability of water-soluble ruthenium–phosphine complex catalysts in multiphase selective hydrogenation of cinnamaldehyde using toluene and pressurized carbon dioxide
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DOI：
10.1016/j.molcata.2006.01.022
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发表时间：
2006-04
影响因子：
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通讯作者：
S. Fujita;Shuji Akihara;M. Arai
中科院分区：
文献类型：
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作者：
S. Fujita;Shuji Akihara;M. Arai
以水-甲苯和水-加压二氧化碳为反应体系，考察了水溶性铑膦络合物催化剂在反式肉桂醛（CAL）选择加氢反应中的循环使用性能。对于第一次加氢运行，肉桂醇（COL）的选择性是高的甲苯和稠密CO2，因为界面催化，其中反应主要发生在水相和其他甲苯或稠密CO2相之间的界面。总CAL转化率和COL选择性在第二次运行时降低，对于稠密CO2比甲苯更显著。然而，在随后的运行中，观察到不太显著的变化。在第一次加氢过程中，活性金属配合物通过COL主产物的积累而转变为活性较低的配合物，如Ru（H）2Ln（TPPTS）m（L=COL），这种结构变化在CO2多相加氢中比在甲苯多相加氢中更容易发生，这可能是因为在CO2气相中的溶解度比在甲苯中的溶解度更小。对于COL在水相中的均相反应，Ru（H）_2Ln（TPPTS）催化COL异构化生成HCAL，而催化氢化生成氢化肉桂醇。然而，对于这些配合物，COL的选择性仍然与HCAL的多相氢化反应相当，因为CAL的两性底物的氢化主要发生在水与甲苯或稠密CO2气相之间的界面处。CO2分子与CAL的相互作用也会增加底物羰基的反应活性。
The recyclability of water-soluble ruthenium–phosphine complex catalysts was investigated in water–toluene and in water–pressurized carbon dioxide systems for selective hydrogenation of trans-cinnamaldehyde (CAL). For the first hydrogenation run, the selectivity for cinnamyl alcohol (COL) is high for both toluene and dense CO2, because of interfacial catalysis in which the reaction mainly occurs at the interface between the aqueous phase and the other toluene or dense CO2phase. The total CAL conversion and the COL selectivity decrease on the second run, more significantly with dense CO2than toluene. On the subsequent runs, however, less significant changes were observed. During the first run, the active metal complexes should change to much less active ones such as Ru(H)2Ln(TPPTS)m(L=COL) by accumulation of the main product of COL. This structural change may occur more easily in multiphase hydrogenation with dense CO2than that with toluene, probably because the solubility in the dense CO2gas phase is even smaller than that in toluene. For homogeneous reaction of COL in aqueous phase, Ru(H)2Ln(TPPTS)mcatalyzes the isomerization to HCAL compared with the hydrogenation to hydrocinnamyl alcohol. With those complexes, however, the selectivity for COL is still comparable to that for HCAL for multiphase hydrogenation reactions because the hydrogenation of an ampholytic substrate of CAL occurs mainly at interface between water and toluene or dense CO2gas phase. Interactions of CO2molecules with CAL would also increase the reactivity of carbonyl group of the substrate.