Department of Chemical & Biological Engineering, Sir Robert Hadfield Building, The University of Sheffield, Sheffield S7 2GA, United Kingdom ; Department of Chemical and Environmental Engineering, The University of Nottingham, Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor Darul Shsan, Malaysia.
Department of Chemical & Biological Engineering, Sir Robert Hadfield Building, The University of Sheffield, Sheffield S7 2GA, United Kingdom.
Beilstein J Org Chem. 2013 Dec 17;9:2886-97. doi: 10.3762/bjoc.9.325. eCollection 2013.
The palladium metal catalysed Heck reaction of 4-iodoanisole with styrene or methyl acrylate has been studied in a continuous plug flow reactor (PFR) using supercritical carbon dioxide (scCO2) as the solvent, with THF and methanol as modifiers. The catalyst was 2% palladium on silica and the base was diisopropylethylamine due to its solubility in the reaction solvent. No phosphine co-catalysts were used so the work-up procedure was simplified and the green credentials of the reaction were enhanced. The reactions were studied as a function of temperature, pressure and flow rate and in the case of the reaction with styrene compared against a standard, stirred autoclave reaction. Conversion was determined and, in the case of the reaction with styrene, the isomeric product distribution was monitored by GC. In the case of the reaction with methyl acrylate the reactor was scaled from a 1.0 mm to 3.9 mm internal diameter and the conversion and turnover frequency determined. The results show that the Heck reaction can be effectively performed in scCO2 under continuous flow conditions with a palladium metal, phosphine-free catalyst, but care must be taken when selecting the reaction temperature in order to ensure the appropriate isomer distribution is achieved. Higher reaction temperatures were found to enhance formation of the branched terminal alkene isomer as opposed to the linear trans-isomer.
钯金属催化的 4-碘苯甲醚与苯乙烯或甲基丙烯酸甲酯的 Heck 反应在连续的 plug flow 反应器（PFR）中进行，使用超临界二氧化碳（scCO2）作为溶剂，THF 和甲醇作为改性剂。催化剂为 2%负载在二氧化硅上的钯，碱为二异丙基乙胺，因为它可溶于反应溶剂。未使用膦配体作为共催化剂，因此简化了后处理程序，并提高了反应的绿色信誉。反应研究了温度、压力和流速的函数，并在与苯乙烯的反应中与标准的搅拌高压釜反应进行了比较。测定了转化率，在与苯乙烯的反应中，通过 GC 监测了异构产物分布。在与甲基丙烯酸甲酯的反应中，将反应器从 1.0 毫米内径放大到 3.9 毫米内径，并测定了转化率和周转频率。结果表明，钯金属、无膦配体催化剂可有效地在 scCO2 中进行 Heck 反应，但在选择反应温度时必须小心，以确保达到适当的异构体分布。发现较高的反应温度会增强支链末端烯烃异构体的形成，而不是线性反式异构体。
