The effect of ring size on the selective carboxylation of cycloalkene oxides
The effect of ring size on the selective carboxylation of cycloalkene oxides
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DOI：
10.1039/c6cy02448c
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发表时间：
2017-03
影响因子：
5
通讯作者：
R. Alsaiari;L. Perrott;E. Nowicka;Rebecca V. Engel;Peter J. Miedziak;S. Kondrat;J. Edwards;D. Willock
中科院分区：
文献类型：
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作者：
R. Alsaiari;L. Perrott;E. Nowicka;Rebecca V. Engel;Peter J. Miedziak;S. Kondrat;J. Edwards;D. Willock
二氧化碳利用技术可以通过从烟道气中封存二氧化碳和间接缓解化学制造中传统原料的压力来降低大气中的二氧化碳水平。一种有前途的方法是利用CO2与合适的环氧化物反应来生产有价值的环状碳酸酯（CC）。这也具有二氧化碳替代有毒和危险的反应物如光气的优点。在早期的工作中，我们研究了在无溶剂条件下使用负载的金和金-钯纳米颗粒作为催化剂和来自空气的氧气作为氧化剂从环烯烃合成环氧化物。环氧化物选择性对环尺寸的强烈依赖性被观察到，其中C5 < C6 < C7 <C8。在这项研究中，我们扩展这项工作的调查环加成的CO2到不同的环烯氧化物的最终目的是设计一个过程中，既环氧化的烯烃和CO2的掺入可以在一个单一的过程中实现。然而，我们已经发现了对碳酸酯的选择性的相反趋势：较小的环氧化环烯烃给出最高的碳酸酯选择性，而大的环根本不产生CC。的产品分布表明，一个替代的开环的环氧化物，以产生醇和酮是优选的，在所有的实验条件下探索较大的环系统。此外，使用DFT方法研究了使用季铵盐和ZnBr 2作为催化剂体系的CC合成的机理。计算结果支持了实验结果。
Carbon dioxide utilisation technology can contribute to the reduction of atmospheric CO2 levels both through its sequestration from flue gases and indirectly by relieving pressure on conventional feedstocks in chemical manufacturing. A promising approach is to employ CO2 to produce valuable cyclic carbonates (CCs) in reaction with suitable epoxides. This also has the advantage that carbon dioxide replaces toxic and hazardous reactants such as phosgene. In earlier work we have investigated the synthesis of epoxides from cycloalkenes using supported gold and gold–palladium nanoparticles as catalysts and oxygen from air as the oxidant under solvent free conditions. A strong dependence of epoxide selectivity on ring size was observed with C5 < C6 < C7 ≪ C8. In this study we extend this work to the investigation of cycloaddition of CO2 to different cycloalkene oxides with the ultimate aim of designing a process in which both epoxidation of an alkene and incorporation of CO2 could be achieved in a single process. However, we have found the opposite trend for the selectivity to carbonates: smaller ring cycloalkene oxides giving the highest carbonate selectivities while large rings do not yield CCs at all. The product distributions suggest that an alternative ring opening of the epoxides to yield alcohols and ketones is preferred under all the experimental conditions explored for larger ring systems. Additionally, the mechanism of the CC synthesis using a quaternary ammonium salt and ZnBr2 as the catalyst system was investigated using DFT methods. The results of the calculations support the experimental findings.