Green Chemistry Blog

Carbon dioxide is used to promote the oxidation reactions of several cyclic alkenes

Carbon dioxide enhances the catalytic oxidation of cyclic alkenes, leading to higher conversions at low pressures, say researchers from South Korea. The system could be a step towards new technology for using CO₂ at low pressures.

Sang-Eon Park and coworkers from Inha University, Incheon, prepared carbon nitrides that contain surface groups to activate the CO₂, which was then used to promote the oxidation reactions of several cyclic alkenes.

CO₂ is being recognised as an alternative and economic resource for use in organic reactions and it has been used in catalytic reactions, either as a solvent or a reagent. However, in most cases, it is used in a dense phase or under supercritical conditions, which require high operating pressures and have low reaction rates. 

The team tested their system by oxidising different cyclic alkenes with various amounts of oxygen, with and without CO₂,  and compared the results. They found that the presence of the CO₂ increased the conversion percentage in all cases. The CO₂ acts as an oxygen source, which is inferred from the formation of carbon monoxide and surface carbamate. The team was also able to reuse the catalyst up to three times.

Chang-jun Liu from Tianjin University, China, an expert in catalysis and the use of greenhouse gases, says that using ‘high nitrogen containing carbon nitrides to enhance the oxidation of cyclic olefins with CO₂ as a soft oxidant’ is significant. Liu adds that the work could lead to an easy approach for CO₂ conversion with the production of highly-valued chemicals.

Park’s team now hopes to fully understand the reaction mechanism, explaining that this will help them to design a more appropriate catalyst. ‘Further spectroscopic and computational studies are in progress and hopefully, very soon, a complete insight over promotional aspects will be revealed,’ concludes Park.

Reproduced from a Chemistry World story written by Mary Badcock

Read the full article here:

CO₂ activation and promotional effect in the oxidation of cyclic olefins over mesoporous carbon nitrides
Mohd Bismillah Ansari, Byung-Hoon Min, Yong-Hwan Mo and Sang-Eon Park
Green Chem., 2011, Advance Article
DOI: 10.1039/C0GC00951B

Scientists from Bejing, China, have developed a highly selective supported Ru catalyst for the hydrogenation of benzene to cyclohexene – a compound which is very useful for nylon production. Until now, the Ru based catalysts used for this transformation deliver low selectivity and yield of the desired partial hydrogenation product, and often the use of additives is necessary. However, in this work by Buxing Han and co-workers, cyclohexene yields of 56% were achieved in water without the use of additives.

The selective hydrogenation of benzene to cyclohexene is challenging, as it is significantly more thermodynamically favorable for cyclohexane to be the primary product of the reaction. By using water as the reaction medium it is proposed that the hydrogenation of cyclohexene to cyclohexane is slowed because benezene is more soluable than cyclohexene in water under these conditions. This is also aided by the hydroxyl groups on the catalyst surface which disfavour the adsorption of cyclohexene onto the catalyst surface, thus preventing further hydrogenation. Synergistic effects between the zinc and zirconium in the catalyst support also play a crucial role in the efficiency and selectivity of the catalyst used in this work.

Read the full article for free until 22nd April by following the link below.

Highly selective benzene hydrogenation to cyclohexene over supported Ru catalyst without additives, Huizhen Liu, Tao Jiang, Buxing Han, Shuguang Liang, Weitao Wang, Tianbin Wu and Guanying Yang, Green Chem., 2011, DOI:10.1039/c0gc00959h