Flow system overcomes reagent incompatibility issues


Synthesising cyclic carbonates could become easier and more efficient thanks to a sequential flow system developed by scientists in the US.

Cyclic carbonates are used as fuel additives and in lithium-ion batteries, and are key intermediates for pharmaceuticals. However, many current synthesis methods require expensive starting reagents and result in unwanted side products.

The method developed by Tim Jamison, of Massachusetts Institute of Technology in Boston, and coworkers, avoids many of these problems by starting from easily obtainable alkenes, rather than the corresponding epoxides, and the cheap and readily available carbon dioxide. The starting alkene is treated with water and N-bromosuccinimide (NBS), a source of bromide ions, which converts the alkene to a bromohydrin. 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), a base, is then added, followed by CO2, leading to the formation of the cyclic carbonate.

Introducing reagents at specific stages prevents them from interacting with each other or with reaction intermediates

Preliminary experiments revealed that when all the reagents are mixed together, as they would be in a batch system, NBS and DBU tend to react with one another, decreasing their availability and hence the overall yield. The flow system helps to overcome these problems by introducing the reagents sequentially, rather than simultaneously.

Another advantage of the flow system is the enhanced mixing it provides. ‘If you opened up the reactor you would see alternating streams of liquid and gas, called slugs, and because there are so many of them the mixing between the slugs is very efficient,’ explains Jamison. This increases the reaction rate compared to a batch system.

The reaction is both rapid and versatile, and can already be carried out on a very wide range of substrates to make a huge variety of cyclic carbonates, but Jamison says the next step is to increase its scope even further.

Michael North, an organic chemist at the University of York in the UK, says that, whilst the use of NBS means that the synthesis is still not very green, the study is nonetheless promising. ‘Demonstrating that the transformation can be achieved in a two-step flow reactor is a step forward and may lead to future work using truly green and catalytic oxidants.’

References

This paper is free to access until 12th March 2014. Download it here:

T Jamison et al, Chem. Sci., 2014, DOI: 10.1039/c3sc53422g


Related Content

New catalyst converts waste CO2 to useful molecules

9 October 2009 News Archive

news image

UK scientists develop super-efficient catalyst to convert waste CO2 from power stations into useful cyclic carbonates

Going with the flow

31 March 2012 Premium contentFeature

news image

When it comes to scaling up organic synthesis, it pays to think small

Most Read

Z machine puts the squeeze on metallic deuterium

25 June 2015 Research

news image

Pressures similar to those at centre of the Earth forge metallic deuterium in step toward 80-year-old dream of creating metal...

First pictures of hydrogen bonds unveiled

26 September 2013 Research

news image

Observation of intermolecular interactions in quinolines could help to settle the nature of this kind of bonding

Most Commented

Collaboration, not competition

29 June 2015 Research

news image

Organic chemist E J Corey talks to Phillip Broadwith about awards, ambition and academic freedom

Z machine puts the squeeze on metallic deuterium

25 June 2015 Research

news image

Pressures similar to those at centre of the Earth forge metallic deuterium in step toward 80-year-old dream of creating metal...