1 PUSH Bulletin DuPont FluoroIntermediates DuPont HFPO. Properties, Uses, Storage, and Handling Introduction Properties hexafluoropropylene oxide (HFPO) is a versatile HFPO supplied by DuPont has a minimum purity of fluorointermediate that can be used in the synthesis wt% (Table 1). When impurities are detected of fluoromonomers, fluoropolymers and to add fluo- they generally consist of hexafluoropropene (HFP). rine functionality to a variety of organic precursors. HFP is the key chemical precursor to HFPO which Perfluorinated vinyl ethers utilized in the production is synthesized in an oxidation process. This product of commercial fluoropolymers are produced using may also contain a very low level of hexafluoro- HFPO as the key intermediate. In addition, the acetene (HFA), which is a potential reproduction commercial perfluorinated Krytox lubricant has hazard.
2 The HFA isomer is generated by a metal HFPO as the monomer unit. Other useful commer- catalyzed mechanism that can be initiated by im- cial fluorointermediates produced from HFPO in- proper storage and handling methods. See Storage clude hexafluoroisopropanol, hexafluoroisobutylene section and MSDS for more information. and bisphenol AF. All of these FluoroIntermediates Physical properties of HFPO are given in Table 2. are commercially available through DuPont . HFPO is a nonflammable gas that is stored as a pressurized liquid. The vapor pressure equilibrium curve for HFPO is included in Figure 1. Table 1. Product Data Property Unit Min. Max. Organic Purity HFPO Weight % - HFP (Hexafluoropropene) Weight % Table 2. Physical Properties Property Unit Typical Value Chemical Name Oxirane, Trifluoro (Trifluoromethyl).
3 CAS No. 428-59-1. EINECS No. 207-050-4. O. F. Chemical Formula F2C C. CF3. Molecular Weight 166. Boiling Point @ 1 atm C ( F) 27 ( 17). Vapor Pressure @ 25 C kPa-abs (psia) 660 (96). Melting Point C ( F) 144 ( 227). Liquid Density @ 25 C kg/m3 (lb/ft3) 1300 ( ). Vapor Heat Capacity @ 25 C J/mol K 138. Liquid Heat Capacity @ 25 C J/mol K 172 (estimated). Heat of Vaporization @ NBP KJ/mol Critical Temperature C ( F) 86 ( ). Critical Pressure kPa abs (psia) 2896 (420). Critical Density g/cc Flammability Limits Vol% None Exposure Limits HFPO, AEL 8hr. TWA* ppm 20. * AEL is the DuPont 's internally used Acceptable Exposure Limit. Where governmentally imposed occupational exposure limits which are lower than the AEL are in effect, such limits shall take precedence. TWA = Time weighted average The DuPont Oval Logo, DuPont , Krytox , and The miracles of science , are trademarks or registered trademarks of du Pont de Nemours and Company.
4 Figure 1. HFPO Vapor Pressure, est. Abs press (psia) 600. 500. 400. 300. 200. 100. 0. -20 0 20 40 60 80 100. Temp (C). Figure 2. Infrared Spectrum of hexafluoropropylene oxide Vapor at kPa in a 10 cm cell Figure 3. Infrared Spectrum of Hexafluoroacetone Vapor at kPa in a 10 cm cell Uses Ring-opening the HFPO with halogenating reagents hexafluoropropylene oxide (HFPO) is a key inter- such as Me3 SiI gives halogenated perfluoroalkyl- mediate in the synthesis of organofluorine com- propionic acid derivatives such as CF3 CFIC(O)F. C. pounds. Many commercial fluoropolymers use C). HFPO either as a monomer or a monomer precur- O O. sor. The epoxide ring is opened by nucleophiles to F SiMe3I. give a variety of derivatives. HFPO may be isomer- F2C C CF3 CFC F. ized to either pentafluoropropionyl fluoride (PPF) CF3 I.
5 Or hexafluoroacetone (HFA). The thermolysis of HFPO can also serve as a source of difluoro- carbene. A few examples of HFPO chemistry HFPO can serve as a source of the heptafluoro- are given below; the chemistry of HFPO has propoxide ion owing to the equilibrium between been ,2 PPF and fluoride ion in solution. The heptafluoro- propoxide ion, as well as other polyfluorinated Reactions of HFPO alkoxides, open the HFPO ring to generate oligo- HFPO is easily isomerized to pentafluoropropionyl mers which can be isolated as the acid fluoride (PPF) by nucleophilic catalysts such as The acid fluorides in turn may be converted to halides or vinyl ethers which are themselves useful chemical intermediates. O O. A). F. F2C C CF3CF2C F. O O. Catalyst RfOM. CF3 D) F. CF2 C RfO(CFCF2O)n CF C F.
6 M = Na+, K+, Cs+. In the presence of alcohols or secondary amines, CF3 CF3 CF3. derivatives of PPF are formed. Methyl 2,3,3,3- tetrafluoro-2-methoxy propionate, prepared from RfO(CFCF2O)n CF. methanol and HFPO, may be converted to methyl CF3 CF2. 3,3,3-trifluoropyruvate, a useful building block in organofluorine chemistry. B. O In the presence of Lewis acids such as SbF5, HF or NR2H. CF3CF2C NR2 ACl xF3 x (x = ), HFPO isomerizes to This can even happen in storage containers B) O if precautions are not taken to prevent the rear- F rangement reaction from occurring. F2 C C. E). CF3 O O. ROH F Lewis Acid O O F2C C C. oleum CF3CF(OR)C OR CF3C(O)C OR CF3 CF3 CF3. Thermolysis of HFPO gives difluorocarbene and trifluoroacetyl The difluorocarbene may be generated in situ to prepare useful intermediates such as CF2I2 or cyclopropanes.
7 F). O O. F . + :CF2. F2C C C. CF3 F. CF3. Storage and Handling Shipping containers in the hexafluoropropylene oxide is a liquefied, nonflammable compressed gas. According to the Department of Transportation (DOT), a nonflammable compressed gas is defined as a nonflammable material having an absolute pressure greater than 40 psia at 21 C (70 F) and/or an absolute pressure greater than 104 psi at 54 C (130 F). The appropriate DOT designation is as follows: Proper shipping name: Liquefied Gas, hexafluoropropylene oxide Hazard Class: UN. No. 3163. DOT Labels Nonflammable gas DOT Placards Nonflammable gas Containers Water DOT Neight Weight Liquid Dip Phase Capacity Dimensions Specification HFPO Tube Available 760 L 208 cm L x 76 cm D 110A500W 818 kg Yes Liq or Vap 760 L 208 cm L x 76 cm D 106A500W 818 kg Yes Liq or Vap 17,000 L m x m x m L (frame) 51 15,000 kg Yes Liq or Vap ISO m L x m OD.
8 Smaller sizes are available upon request for developmental purposes. There are two types of 760 L cylinders used for shipping HFPO. They are designated by the DOT specifi- cations 110A500W and 106A500W and are identical in dimensions and only differentiated by the position of the valves, relief valves and plugs. It is important to note the location of the cylinder relief valves (RVs). The relief valve should be positioned along a vertical axis aligned with the cylinder valves such that the cylinder relief valve is at the highest point. This ensures that the RV will pass vapor if venting occurs and it will minimize the amount of liquid remaining in the cylinder after use. The black stripe with this side up text is painted on each cylinder to serve as a reminder. Valve, Relief Valve, and Plug Placement for 760 L Cylinders A) 110A500W - Silver with Black Stripe FRONT BACK.
9 B) 106A500W - Silver with Black Stripe FRONT BACK. KEY. relief valve valve plug hexafluoropropylene oxide 5. To reduce the rearrangement of HFPO to Rearrangement Concerns HFA, carbon steel cylinders should be main- hexafluoropropylene oxide can rearrange to the tained below 25 C (77 F). potential reproductive hazard hexafluoroacetone 6. To reduce rearrangement of HFPO to HFA, it (HFA) in the presence of Lewis acids. This can is recommended that product shipped in carbon occur in shipping containers, storage vessels, or steel containers be used within 90 days of other process equipment. Because higher tempera- tures cause faster rearrangement, it is highly recom- 7. Skin contact with HFPO liquid or escaping mended to maintain the HFPO below 25 C (77 F) vapor can lead to frostbite.
10 Unless required for process purposes ( purifica- 8. Never heat a container to temperatures higher tion or chemistry). than 45 C (113 F). Corrosion by-products in carbon steel containers 9. Maintain filled containers with the correct can catalyze the HFPO rearrangement to HFA. In orientation as indicated on cylinders to ensure order to inhibit the rearrangement reaction, toluene relief protection is located in the vapor phase. is commonly added to carbon steel containers. Low 10. Never apply direct flame or live steam to a levels of toluene have been shown to be effective container or valve. as an inhibitor in this rearrangement reaction. If the 11. Never refill disposable cylinders with anything. end user requires even lower levels of toluene, a The shipment of refilled disposable cylinders is special low toluene grade can be selected, but it is prohibited by DOT regulations.