As the regular reader of F-Blog knows, fluorous liquid-liquid extraction (FLLE) is, along with fluorous solid phase extraction (FSPE) one of the primary methods to conduct fluorous separations. In fact, FLLE was the original fluorous separation method as applied to fluorous biphasic catalysis. Traditionally, perfluoroalkanes were the solvents used and the fluorous compounds were termed “heavy” fluorous compounds due to the large number of fluorous chains which were often necessary to effect good partitioning between the fluorous phase and the organic phase. As we learned more about fluorous separations and partitioning, solvent tuning techniques using hydrofluoroethers (HFE’s) in conjunction with perfluoroalkanes led to a dramatic reduction in the number of fluorous chains necessary. Solvent tuning is a big advance in FLLE methods since it is considerably easier than substrate tuning by adding more fluorous chains.
Great. So what fluorous solvents are commercially available and where can I get them?
Well, not from Fluorous Technologies, Inc. since we do not actually carry any fluorous solvents. These materials, however, are readily available from a number of sources. For example, perfluorohexane, known as FC-72, is available in research quantities from a number of different vendors including Sigma-Aldrich, Acros Organics, and Matrix Scientific. Larger quantities of FC-72 and other related perfluoroalkanes are available from 3M. Perfluoroalkanes are available in a number of different chain lengths to provide a range of boiling points and other physical characteristics. Many are mixtures of linear and branched isomers, but some such as perfluoromethylcyclohexane (PFMC) are single isomers and have been commonly used in fluorous partitioning studies.
For solvent tuning, we have found that hydrofluoroethers, such as nonafluorobutyl methyl ether, known as HFE-7100, are a great choice. These solvents are miscible with common organic solvents but when used with perfluoroalkanes form a fluorous layer that is more polar than the perfluoroalkane alone. By combining a more fluorophobic organic phase with a more polar fluorous phase, the number of fluorous chains required for FLLE is substantially lowered. Like perfluoroalkanes, the HFE’s are also available in different chain lengths providing a range of physical characteristics. These are also available from different vendors and from 3M.
Below are some links to some of the more common fluorous solvents used in FLLE (for bulk quantities please click on the 3M links above):