1. CHEM 2017 2008 lect 7 + 8 F chemicals

2.  HYDROGEN FLUORIDE  INORGANIC FLUORIDES  FLUORINE

3.  CALCIUM FLUORIDE  KNOWN TO LOWER THE MELTING POINT OF MINERALS (16th C)  Early chemists: HF – glass apparatus attacked  F realised to be similar to Cl (1813), but not isolated  HF first clearly prepared only in 1850s

6. HF  First made by slowly heating POTASSIUM HYDROGEN FLUORIDE  EARLY USE OF HF IN ETCHING GLASS  1930S INTRODUCTION OF CHLOROFLUOROCARBONS AS REFRIGERANTS

7. MANHATTEN PROJECT  USE OF UF 6 FOR 235 U ENRICHMENT  235 U vs 238 U  GAS CENTRIFUGES – SLIGHTLY DIFFERENT DIFFUSION RATES  CONTAINMENT VESSELS – FOR CORROSIVE F-CONTAINING COMPOUNDS – PERFLUORO ORGANIC COMPOUNDS FOUND TO BE SUITABLE

8. CFCs - environmental problems  CFCs relatively stable  When released rise through earth’s atmosphere unchanged  In the stratosphere generate Cl radicals, that destroy ozone in a catalytic action  Montreal Protocol  Replace CFCs with HCFCs  Less stable in the atmosphere – decompose at lower levels

9. FLUORSPAR  CALCIUM FLUORIDE – VARIABLE PURITY  USED IN STEEL MAKING SINCE 1860s  Metallurgical grade: 60-80%  Ceramic grade (glass) 85-95%  Acid grade: 97+% (HF manufacture)

10. FLUORSPAR  Helps separation of metal in steel production from slag and impurities such as P, S, Si removed as their oxides  Also used in Cu, Sn, Zn refining  Used in glass (small crystals of calcium fluoride render glass milky) - also fluorides can be added to adjust coefficients of expansion of glass

11. PRODUCTION OF HF  HF - ANHYDROUS OR AQUEOUS SOLUTION  CaF 2 + H 2 SO 4  CaSO 4 + 2HF  30m long reactor for 20kt yr -1  Crude acid purified  Calcium sulphate: neutralise with lime – historically sent to landfill; now more uses examined e.g. self-levelling floor coatings

13. HF  Very highly corrosive  Extreme precautions needed in handling to avoid contact with skin – eats into bones – very serious burns and bone damage  Fairly volatile b pt: 19C

14. CFC / HCFCs  Programme of replacing CFCs well organised depending on application  Catalytic processes being developed to convert old product to new product  Fluorinated chromia

18. CFC conversion  Equilibrium limited by HCl formation  Separate desired product from HCl and recycle  Conversion per pass 10-20% but selectivity is high - very few by-products

19. Other uses of HF  Electrochemical fluorination:  Aliphatic hydrocarbon conversion to perfluoro-substituted systems by electrolysis using liquid anhydrous HF  e.g. C 8 H 17 SO 2 F  C 8 F 17 SO 2 F as an intermediate for surfactants, textile treatments, surface coatings  e.g. C 7 F 15 COF used in teflon manufacture

20. TEFLON  Poly(C 2 H 4 ) = polyethylene  Poly(C 2 F 4 ) = teflon

21. Perfluorohydrocarbon derivatives  More stable than hydrocarbon equivalents  Thermal shock resistance is higher (COMPUTER CHIP TESTING)  COOLING FOR SUPERCOMPUTERS  SYNTHETIC OXYGEN CARRIERS (Artificial blood in surgical procedures)

22. HF  Aromatic fluorocarbons  Balz-Schiemann diazotation reaction as a procedure for introducing F onto an aromatic ring  Used in drug synthesis

23. HF  In aluminium production:  Synthetic cryolite, Na 3 (AlF 6 ) as the fused salt used to dissolve alumina in Al manufacture  As an acid catalyst in hydrocarbon conversions:  Petroleum refining, C 4  branched C 8 alkanes for high octane gasoline

24. HF refining catalysts  HF more efficient catalyst than sulphuric acid, 0.068kg rather than 0.23kg  Fewer by-products  Easier separation  [Solid acid catalysts even more desirable – ease of handling, less dangerous]

25. HF MISCELLANEOUS USES  Scale removal from stainless steel  Oil-well acidification: improved flow rate of oil as wells become depleted  Etching of electronic chips  UF 6 production (nuclear fuel)  Frosted light-bulbs  Manufacture of various inorganic fluorides

26. INORGANIC FLUORIDES  F is highly reactive  High electronegativity: high oxidation state of metals reached easily  F - anion very small, so high coordination number possible  Wide range of M-F bond strengths possible so very diverse range of compounds possible

27. FLUORINE AND FLUORIDES IN SOUTH AFRICA  NECSA  Experience gained in U enrichment  Now more widely applied to manufacture of F-containing chemicals