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Making molecules that twinkle

Date:
February 13, 2016
Source:
The Agency for Science, Technology and Research (A*STAR)
Summary:
A single step process transforms carbon dioxide into star-shaped molecules that are promising building blocks for useful polymeric materials, report scientists.
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Single step process transforms carbon dioxide into star-shaped molecules that are promising building blocks for useful polymeric materials.

The power of carbon dioxide has been harnessed by Singapore's Agency for Science, Technology and Research (A*STAR) researchers to make two symmetrical star-shaped molecules in a single step. These molecules could be used to build complex, functional polymeric materials useful for catalysis, coatings and drug delivery.

Carbon dioxide is a cheap and accessible base material, explains lead researcher He-Kuan Luo from the A*STAR Institute of Materials Research and Engineering. "Therefore, many people are searching for efficient methods to transform carbon dioxide into useful molecules," he explains. "But transforming carbon dioxide is not typically easy."

His team has developed a simple route to use carbon dioxide to make aromatic compounds that can be used as building blocks for more complicated materials. They created symmetrical benzene rings with three or six identical arms comprising carbonate groups terminated by carbon-carbon triple bonds, or 'alkynes'. "We can integrate the carbon dioxide into the molecule without the need for high temperatures or high pressure," says Luo.

The molecules were made in a single step. The team introduced carbon dioxide from dry ice to an alcohol with an alkyne end group and benzene rings decorated with either three or six alkyl bromide groups. "At the beginning, however, only some of the branches reacted so we could not get the desired compound," Luo explains.

The team fine-tuned the process and found the reactions worked most efficiently at room temperature, with the carbon dioxide at atmospheric pressure and with the addition of both a promoter tetrabutylammonium bromide (TBAB) and the base potassium carbonate. "We tried many times and after a few months, we finally got [the bromide groups in] all six branches to react [with the alcohol]," he says.

Adding the promoter to the mix doubled the product produced. "It is likely that the tetrabutylammonium cation enhances the rate of carbon dioxide incorporation by stabilizing the carbonate anion," says Luo.

The reaction time is also vital. "We needed to be patient and let the reaction run to completion to ensure that all the branches reacted." The synthesis of the three-armed and six-armed star-shaped molecule took two and four days respectively.

The alkynes on the end of each arm in these molecules should theoretically be able to react with a host of different molecules using simple click chemistry -- to produce a range of complex or functional materials. "We are currently trying to use the six-armed branched molecule to build more functional star-shaped molecules, which may find applications in catalysis, coatings and drug delivery," says Luo.


Story Source:

The above post is reprinted from materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Content may be edited for style and length.


Journal Reference:

  1. Rebecca Shu Hui Khoo, Agnes Mei Xian Lee, Pierre Braunstein, T. S. Andy Hor, He-Kuan Luo. A facile one-step synthesis of star-shaped alkynyl carbonates from CO2. Chem. Commun., 2015; 51 (56): 11225 DOI: 10.1039/C5CC04088D

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The Agency for Science, Technology and Research (A*STAR). "Making molecules that twinkle." ScienceDaily. ScienceDaily, 13 February 2016. <www.sciencedaily.com/releases/2016/02/160213075330.htm>.
The Agency for Science, Technology and Research (A*STAR). (2016, February 13). Making molecules that twinkle. ScienceDaily. Retrieved August 28, 2016 from www.sciencedaily.com/releases/2016/02/160213075330.htm
The Agency for Science, Technology and Research (A*STAR). "Making molecules that twinkle." ScienceDaily. www.sciencedaily.com/releases/2016/02/160213075330.htm (accessed August 28, 2016).