Phase vanishing and triphasic reactions are ones that employ a fluorous liquid membrane, generally a perfluorocarbon such as FC-72, which separate two other liquid phases. Usually one phase contains a reactant while the other a substrate. The reactant can then migrate across through the fluorous liquid phase and react with the substrate in a controlled manner. Once the reactant phase has completely crossed the fluorous phase into the substrate phase, the reaction is complete and your triphasic system is now biphasic. Hence the name phase vanishing. Phase vanishing reactions have been used for halogenations, cyclopropanations, and Friedel-Crafts acylations to name a few examples. For a prior blog post on phase vanishing, please click here.
A report from Van Zee and Dragojlovic in Organic Letters describes a new twist on the phase vanishing reaction. They replaced the fluorous liquid phase with PTFE in the form of Teflon tape. The same principle applies with the Teflon tape serving as a barrier to keep the reactant and substrate phases separated. (The replacement of a fluorous liquid phase with Teflon tape is reminiscent of the work conducted by Prof. John Gladysz who has demonstrated that Teflon tape can be used as a fluorous media in the capture and recycling of fluorous catalysts. ) The researchers decided to use bromination as their primary reaction, although a couple of acylation reactions were also included. Essentially, they plugged one end of a tube with Teflon tape and filled the tube with bromine. The tube was then immersed into the substrate phase and diffusion of the phases across the Teflon tape resulted in a controlled reaction. The rate of reaction is dependent on the rate of transport across the tape and if the reaction were found to occur to quickly the rate could be modulated by the addition of more layers of Teflon tape.
One thing they did not do was to see if the Teflon tape could be used in a triphasic reaction as described by Prof. Curran. In the triphasic reaction a fluorous tag is transported across the liquid membrane and then detagged leaving the detagged molecule unable to cross back into initial phase. It would be interesting to see if that would work also using Teflon tape.