Ionic liquids

Chemists at Rutgers have developed room temperature ionic liquids that can perform many of the same functions as organic, petroleum-based solvents but will not burn or evaporate into the atmosphere.

The chemicals could be used in industries such as chemical and pharmaceutical manufacturing, electroplating, pulp and paper production, and radioactive waste handling.

A major barrier to widespread adoption of RTILs is that they are significantly thicker – or more viscous – than common organic solvents, such as acetone, alcohol or benzene. The Rutgers scientists invented a variant of these chemicals that could help them overcome this problem.

"RTIL viscosity compares to traditional solvents the way honey compares to water," Castner said. "It impedes their flow, making lab procedures more difficult and manufacturing steps more energy intensive and costly. We have discovered that by substituting silicon for carbon at a key location in some RTIL molecules, we can cut the liquid's viscosity almost tenfold relative to the same ionic liquid without the silicon substitution."

The molecules invented and studied by the Rutgers chemists are organic salts that are liquid at room temperature. The ionic liquids are comprised of positively charged molecules, or cations, based on a carbon-nitrogen structure known as imidazolium. The scientists paired these cations with negatively charged molecules, or anions, including tetrafluoroborate, a molecular structure of boron and four fluorine atoms, and a more complex structure called bis(trifluoromethylsulfonyl)imide.

On the imidazolium cation, they replaced an alkyl group (a common carbon and hydrogen grouping) with a similar structure that substitutes a silicon atom for the central carbon atom. This weakened the interaction between the ions and resulted in liquid viscosities between two and eight times lower than those for liquids with the alkyl cations when measured near room temperature.

In spite of RTIL's safety and environmental advantages, higher costs could slow their adoption. Still, the Rutgers advance could make these chemicals suitable for some near-term specialty applications even though it may be too early to predict a widespread industrial market for RTILs.

A paper describing the RTILs is posted on the Journal of Physical Chemistry B web site at http:/?/?pubs.acs.org/?cgi-bin/?asap.cgi/?jpcbfk/?asap/?pdf/?jp053930j.pdf. It does, however, require authorisation with a User ID and Password to view it.