The Conversion of Hexafluoropropylene (HFP) to Hexafluoropropylene oxide (HFPO)
Posted by David Offord, Ph.D. on
Hexafluoropropylene (HFPO) is a very useful starting material for the production of many fluorochemicals such as:
1. The synthesis of fluorinated vinyl ether monomers such as PPVE, PSVE, PFVE, PMVE. These ethers are copolymerized with tetrafluoroethylene (TFE) and other fluoroalkenes to form melt-processable plastics, elastomers, and ion-exchange resins.
2. The isomerization of HFPO to hexafluoroacetone (HFA) by hydrogen fluoride is used to synthesize bisphenol AF.
3. The synthesis of perfluoropolyethers (PFPE) by fluoride-catalyzed oligomerization of HFPO. In an alternative method, perfluorinated olefins (e.g.,TFE or HFPO) react photochemically with oxygen to form oligomeric perfluoropolyethers. PFPE oligomers with molecular weights of approximately 500 – 6000 are used as inert fluids, lubricants, and hydraulic fluids in applications that require resistance to high temperature or very corrosive environments.
4. The synthesis of hydrofluoroether solvents, for example, HFE-55-10mec-fc and HFE-449mec-f.
5. The preparation of acyl fluorides, fluoroketones, fluorinated heterocycles, as well as serving as a source of difluorocarbene for the synthesis of numerous cyclic and acyclic compounds.
All known methods for the synthesis of HFPO are based on the reaction of HFP with an oxygen donor. Depending on the type of oxidizing agent, epoxidation can be regarded as a nucleophilic, electrophilic or radical reaction. Below we have graphically presented the commonly used process for the conversion of HFP to HFPO using sodium hypochlorite, water, a phase transfer catalyst, and a co-solvent. As shown, many side reactions can occur resulting in many by-products which are listed as either major or minor. In order to minimize the amount of by-products formed, a flow reactor system is sometimes used but results in the incomplete conversion of HFP to HFPO. Since the boiling points of HFP (-29.5 °C) and HFPO (-27.4 °C) are very similar, extractive distillation must be used to purify the HFPO. Toluene is commonly used as the extractant.
