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6 Properties of fluorinated compounds

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Organic and Inorganic Fluorine Chemistry
This chapter is in the book Organic and Inorganic Fluorine Chemistry
6 PropertiesoffluorinatedcompoundsFluorine is definitely a very special element, which is underlined by the proper-ties of fluorinated species. On the one hand, fluorine gives rise to very stable com-pounds. For example, the ionic NaF is the most stable salt of the AB-type with averyhighmeltingpoint,whereasthemolecularfluoridesCF4andSF6areextremelystableagainsthydrolysis.AnotherfeatureintermsofstabilityisthestrengthofH-F-bridges,thestrongestonefoundinHFitself.However,fluorinecompoundsmayalsobeveryreactive,whichisrepresentedbytheextremeoxidizerPtF6,theonlyexistingPt(VI)-compound. Fluorine generally enables very high oxidation states, not onlyin the aforementioned PtF6, but also in IF7and ReF7, which are the only existing,binary AB7-compounds. In some cases, where high-valent binary element fluoridesareunknownornotaccessible,fluorineenablestheexistenceofrelatedcompoundsby forming oxyfluorides or fluorocomplexes. Interestingly, many of the high-valent,neutralfluoridecompoundsarevolatile.ThetypicalexampleforthisfeaturemaybeUF6,whichisextremelyimportantfortheisotopeenrichmentinnuclearfuelindus-try.Lookingatratherorganicsystems,thelistofspecialfeaturesmaybeeasilycon-tinued.FluoroaceticacidCH2FCOOHisaweakacid,butverytoxic.Ifincorporated,itwillreadilyenterthecitratecycle,whichisthenblocked(cf.Section7.1).Withtwofluorine atoms more, trifluoroacetic acid CF3COOH is a stronger acid, but nontoxic.CF3SO3H,actuallyaderivativeofsulphuricacid,is15ordersofmagnitudestrongerthanconcentratedH2SO4.Itisalsocalled“magicacid.”Ingeneral,organicfluorinecompoundsaresomanifold,thattheirpropertiescannotsimplybesummarizedinafewwords.Nevertheless,anattemptismadetogiveashortoverviewoverimportantcompoundclassesandtheirpropertiesinthefollowingparagraph.SomemoredetailsandofcoursepreparativeapproachestowardfluoroorganicmoleculeswillthenbethesubjectofPartCofthismanuscript.Accordingtoproducedamounts,thegroupofvolatilehydroandhalofluorocar-bonsiscertainlyoneofthemostimportantcompoundclassesinfluoroorganicchem-istry.Thesecompoundshavecommonlybeenusedasblowingagents,however,forenvironmental reasons, this application is strongly regulated nowadays. An impor-tantpropertyofthesemoleculesistheirenthalpyofvaporization,duetowhichtheyarestillusedasrefrigerants.Anotherverybigpartofcompoundscanbecategorizedinthefamilyoffluoropolymers,themostfamousonebeingpolytetrafluoroethylene(PTFE)withoutanydoubt.Theyareimportantmaterialswithahighchemicaldura-bility,astheycaninpartevenwithstanddilutedF2undermildconditions.Apartfromthat,theyareusedfornumerouspurposes,asforexample,theconstructionofreac-tionvesselsinchemistry,theproductionofhigh-performancepartsinengineeringorjustthesimplenonstickcoatingforkitchenutensils.Duetotheirchemicaldurabil-ity,someofthemarealsocommonlyusedasasealingmaterial.Fluorinatedpolymershttps://doi.org/10.1515/9783110659337-007
© 2021 Walter de Gruyter GmbH, Berlin/Munich/Boston

6 PropertiesoffluorinatedcompoundsFluorine is definitely a very special element, which is underlined by the proper-ties of fluorinated species. On the one hand, fluorine gives rise to very stable com-pounds. For example, the ionic NaF is the most stable salt of the AB-type with averyhighmeltingpoint,whereasthemolecularfluoridesCF4andSF6areextremelystableagainsthydrolysis.AnotherfeatureintermsofstabilityisthestrengthofH-F-bridges,thestrongestonefoundinHFitself.However,fluorinecompoundsmayalsobeveryreactive,whichisrepresentedbytheextremeoxidizerPtF6,theonlyexistingPt(VI)-compound. Fluorine generally enables very high oxidation states, not onlyin the aforementioned PtF6, but also in IF7and ReF7, which are the only existing,binary AB7-compounds. In some cases, where high-valent binary element fluoridesareunknownornotaccessible,fluorineenablestheexistenceofrelatedcompoundsby forming oxyfluorides or fluorocomplexes. Interestingly, many of the high-valent,neutralfluoridecompoundsarevolatile.ThetypicalexampleforthisfeaturemaybeUF6,whichisextremelyimportantfortheisotopeenrichmentinnuclearfuelindus-try.Lookingatratherorganicsystems,thelistofspecialfeaturesmaybeeasilycon-tinued.FluoroaceticacidCH2FCOOHisaweakacid,butverytoxic.Ifincorporated,itwillreadilyenterthecitratecycle,whichisthenblocked(cf.Section7.1).Withtwofluorine atoms more, trifluoroacetic acid CF3COOH is a stronger acid, but nontoxic.CF3SO3H,actuallyaderivativeofsulphuricacid,is15ordersofmagnitudestrongerthanconcentratedH2SO4.Itisalsocalled“magicacid.”Ingeneral,organicfluorinecompoundsaresomanifold,thattheirpropertiescannotsimplybesummarizedinafewwords.Nevertheless,anattemptismadetogiveashortoverviewoverimportantcompoundclassesandtheirpropertiesinthefollowingparagraph.SomemoredetailsandofcoursepreparativeapproachestowardfluoroorganicmoleculeswillthenbethesubjectofPartCofthismanuscript.Accordingtoproducedamounts,thegroupofvolatilehydroandhalofluorocar-bonsiscertainlyoneofthemostimportantcompoundclassesinfluoroorganicchem-istry.Thesecompoundshavecommonlybeenusedasblowingagents,however,forenvironmental reasons, this application is strongly regulated nowadays. An impor-tantpropertyofthesemoleculesistheirenthalpyofvaporization,duetowhichtheyarestillusedasrefrigerants.Anotherverybigpartofcompoundscanbecategorizedinthefamilyoffluoropolymers,themostfamousonebeingpolytetrafluoroethylene(PTFE)withoutanydoubt.Theyareimportantmaterialswithahighchemicaldura-bility,astheycaninpartevenwithstanddilutedF2undermildconditions.Apartfromthat,theyareusedfornumerouspurposes,asforexample,theconstructionofreac-tionvesselsinchemistry,theproductionofhigh-performancepartsinengineeringorjustthesimplenonstickcoatingforkitchenutensils.Duetotheirchemicaldurabil-ity,someofthemarealsocommonlyusedasasealingmaterial.Fluorinatedpolymershttps://doi.org/10.1515/9783110659337-007
© 2021 Walter de Gruyter GmbH, Berlin/Munich/Boston

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Foreword VII
  4. Contents IX
  5. Part A: Introduction to fluorine chemistry
  6. Introduction to fluorine chemistry 1
  7. 1 Sources of fluorine in nature 5
  8. 2 Elemental fluorine 9
  9. 3 Hydrogen fluoride 15
  10. 4 Preparation of fluorinated compounds [35] 23
  11. 5 Common solid-state structures of inorganic fluorides [35] 31
  12. 6 Properties of fluorinated compounds 35
  13. 7 Health and environmental aspects of fluorinated compounds 37
  14. 8 19F-NMR – an important analytical tool for fluorine chemists [53, 54] 43
  15. Part B: Inorganic fluorine chemistry
  16. Inorganic fluorine chemistry 53
  17. 9 Main group element fluorides 55
  18. 10 Transition metal fluorides and rare earth metal fluorides 161
  19. Part C: Organic fluorine chemistry
  20. Organic fluorine chemistry 281
  21. 11 Fluoroorganic compounds – unusual properties and versatile applications 283
  22. 12 General reaction types and reagents for the introduction of fluorine 301
  23. 13 Fluorination of aliphatic substrates 319
  24. 14 Fluorination of (hetero-) aromatic compounds 415
  25. 15 Preparation of fluorinated olefins and acetylenes 453
  26. 16 Solutions to study questions 479
  27. Bibliography 537
  28. Index 617
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https://doi.org/10.1515/9783110659337-007

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Foreword VII
  4. Contents IX
  5. Part A: Introduction to fluorine chemistry
  6. Introduction to fluorine chemistry 1
  7. 1 Sources of fluorine in nature 5
  8. 2 Elemental fluorine 9
  9. 3 Hydrogen fluoride 15
  10. 4 Preparation of fluorinated compounds [35] 23
  11. 5 Common solid-state structures of inorganic fluorides [35] 31
  12. 6 Properties of fluorinated compounds 35
  13. 7 Health and environmental aspects of fluorinated compounds 37
  14. 8 19F-NMR – an important analytical tool for fluorine chemists [53, 54] 43
  15. Part B: Inorganic fluorine chemistry
  16. Inorganic fluorine chemistry 53
  17. 9 Main group element fluorides 55
  18. 10 Transition metal fluorides and rare earth metal fluorides 161
  19. Part C: Organic fluorine chemistry
  20. Organic fluorine chemistry 281
  21. 11 Fluoroorganic compounds – unusual properties and versatile applications 283
  22. 12 General reaction types and reagents for the introduction of fluorine 301
  23. 13 Fluorination of aliphatic substrates 319
  24. 14 Fluorination of (hetero-) aromatic compounds 415
  25. 15 Preparation of fluorinated olefins and acetylenes 453
  26. 16 Solutions to study questions 479
  27. Bibliography 537
  28. Index 617
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