Sodium fluoride

Sodium fluoride
Names
IUPAC name
Sodium fluoride
Other names
Florocid
Identifiers
ATC code A01AA01
A12CD01,
V09IX06 (18F)
7681-49-4 Yes
ChEBI CHEBI:28741 Yes
ChEMBL ChEMBL1528 Yes
ChemSpider 5045 Yes
EC number 231-667-8
KEGG C08142 
PubChem 5235
RTECS number WB0350000
UNII 8ZYQ1474W7 Yes
UN number 1690
Properties
NaF
Molar mass 41.988173 g/mol
Appearance White to greenish solid
Odor odorless
Density 2.558 g/cm3
Melting point 993 °C (1,819 °F; 1,266 K)
Boiling point 1,704 °C (3,099 °F; 1,977 K)
36.4 g/L (0 °C);
40.4 g/L (20 °C);
50.5 g/L (100 °C)[1]
Solubility slightly soluble in HF, ammonia
negligible in alcohol, acetone, SO2, dimethylformamide
Vapor pressure 1 mmHg @ 1077 C°[2]
1.3252
Structure
Crystal structure Cubic
Lattice constant a = 462 pm
Molecular shape Octahedral
Thermochemistry
Specific
heat capacity (C)
 46.82 J/mol K
51.3 J/mol K
Std enthalpy of
formation (ΔfHo298)
 -573.6 kJ/mol
-543.3 kJ/mol
Hazards
MSDS [3]
H301, H315, H319[3]
EU Index 009-004-00-7
EU classification T – Toxic
Xi – Irritant
R-phrases R25, R32, R36/38
S-phrases (S1/2), S22, S36, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
0
3
0
Flash point Non-flammable
52–200 mg/kg (oral in rats, mice, rabbits)[4]
US health exposure limits (NIOSH):
TWA 2.5 mg/m3[5]
Related compounds
Other anions
 Sodium chloride
Sodium bromide
Sodium iodide
Other cations
 Lithium fluoride
Potassium fluoride
Rubidium fluoride
Caesium fluoride
Related compounds
 TASF reagent
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Sodium fluoride /ˌsoʊdiəm ˈflʊəraɪd/[6] is an inorganic chemical compound with the formula NaF. A colorless solid, it is a source of the fluoride ion in diverse applications. Sodium fluoride is less expensive and less hygroscopic than the related salt potassium fluoride.

Structure, general properties, occurrence

Sodium fluoride is an ionic compound, dissolving to give separated Na+ and F− ions. Like sodium chloride, it crystallizes in a cubic motif where both Na+ and F− occupy octahedral coordination sites;[7][8] its lattice spacing, approximately 462 pm, is somewhat smaller than that of sodium chloride.

The mineral form of NaF, villiaumite, is moderately rare. It is known from plutonic nepheline syenite rocks.[9]

Production

NaF is prepared by neutralizing hydrofluoric acid or hexafluorosilicic acid (H2SiF6), byproducts of the reaction of fluorapatite (Ca5(PO4)3F) (from phosphate rock) from the production of superphosphate fertilizer. Neutralizing agents include sodium hydroxide and sodium carbonate. Alcohols are sometimes used to precipitate the NaF:

HF + NaOH → NaF + H2O

From solutions containing HF, sodium fluoride precipitates as the bifluoride salt NaHF2. Heating the latter releases HF and gives NaF.

HF + NaF ⇌ NaHF2

In a 1986 report, the annual worldwide consumption of NaF was estimated to be several million tonnes.[10]

Applications

Sodium fluoride is sold in tablets for cavity prevention and treatment of osteoporosis

Treatment of Osteoporosis

Sodium fluoride is used to treat Osteoporosis, particularly in postmenopausal women.[11] It stimulates bone formation and increases bone density in women with osteoporosis by 8 percent per year in the lumbar spine and by 4 percent in the proximal femur, but it decreases cortical bone density in the radius by 2 percent per year.[12] Bone with excess fluoride content has an abnormal structure, and its fragility may be increased. Thus sodium fluoride therapy results in large increases in bone mineral density, but the effect on fracture rates is small.[13][14][15] However there is evidence that using smaller doses of slow release sodium fluoride may be more effective.[16]

Medical imaging

In medical imaging, fluorine-18-labelled sodium fluoride (USP, sodium fluoride F18) is one of the oldest tracers used in positron emission tomography (PET), having been in use since the 1960s.[17] Relative to conventional bone scintigraphy carried out with gamma cameras or SPECT systems, PET offers more sensitivity and spatial resolution. Fluorine-18 has a half-life of 110 min, which requires it to be used promptly once produced; this logistical limitation hampered its adoption in the face of the more convenient technetium-99m-labelled radiopharmaceuticals. However fluorine-18 is generally considered to be a superior radiopharmaceutical for skeletal imaging. In particular it has a high and rapid bone uptake accompanied by very rapid blood clearance, which results in a high bone-to-background ratio in a short time. Additionally the annihilation photons produced by decay of 18F have a high energy of 511-keV compared to 140-keV photons of 99mTc.[18]

Water treatment

Fluoride salts are often added to drinking water (as well as certain food products in some countries) for the purposes of maintaining dental health. The fluoride enhances the strength of teeth by the formation of fluorapatite, a naturally occurring component of tooth enamel.[19][20][21] Although sodium fluoride is used to fluoridate water and, indeed, is the standard by which other water-fluoridation compounds are gauged, hexafluorosilicic acid (H2SiF6) and its salt sodium hexafluorosilicate (Na2SiF6) are more commonly used additives in the U.S.[22] Toothpaste often contains sodium fluoride to prevent cavities, although tin(II) fluoride and sodium monofluorophosphate are generally considered superior for this application.

In Chemistry

A variety of specialty chemical applications exist in synthesis and extractive metallurgy. It reacts with electrophilic chlorides including acyl chlorides, sulfur chlorides, and phosphorus chloride.[23] Like other fluorides, sodium fluoride finds use in desilylation in organic synthesis. Sodium fluoride can be used to produce fluorocarbons via the Finkelstein reaction; this process has the advantage of being simple to perform on a small scale but is rarely used on an industrial scale due the existence of more effective techniques (e.g. Electrofluorination, Fowler process).

Other uses

Sodium fluoride is used as a cleaning agent (e.g., as a "laundry sour").[10] Sodium fluoride is used as a stomach poison for plant-feeding insects. Inorganic fluorides such as fluorosilicates and sodium fluoride complex magnesium ions as magnesium fluorophosphate. They inhibit enzymes such as enolase that require Mg2+ as a prosthetic group. Thus, fluoride poisoning prevents phosphate transfer in oxidative metabolism.[24]

Safety

Fluorides, particularly aqueous solutions of sodium fluoride, are rapidly and quite extensively absorbed.[25]

Fluorides interfere with electron transport and calcium metabolism. Calcium is essential for maintaining cardiac membrane potentials and in regulating coagulation. Large ingestion of fluoride salts or hydrofluoric acid may result in fatal arrhythmias due to profound hypocalcemia. Recreational inhalation of fluoridated hydrocarbon refrigerants like Freon has been associated with "sudden sniffing death", which is thought to be a fatal arrhythmia caused by myocardial sensitization to catecholamines.[26]

Chronic over-absorption can cause hardening of bones, calcification of ligaments, and buildup on teeth. Fluoride can cause irritation or corrosion to eyes, skin, and nasal membranes.[26]

The lethal dose for a 70 kg (154 lb) human is estimated at 5–10 g.[10] Sodium fluoride is classed as toxic by both inhalation (of dusts or aerosols) and ingestion.[27] In high enough doses, it has been shown to affect the heart and circulatory system. For occupational exposures, the Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have established occupational exposure limits at 2.5 mg/m3 over an eight-hour time-weighted average.[28]

In the higher doses used to treat osteoporosis, plain sodium fluoride can cause pain in the legs and incomplete stress fractures when the doses are too high; it also irritates the stomach, sometimes so severely as to cause ulcers. Slow-release and enteric-coated versions of sodium fluoride do not have gastric side effects in any significant way, and have milder and less frequent complications in the bones.[29] In the lower doses used for water fluoridation, the only clear adverse effect is dental fluorosis, which can alter the appearance of children's teeth during tooth development; this is mostly mild and is unlikely to represent any real effect on aesthetic appearance or on public health.[30] A chronic fluoride ingestion of 1 ppm of fluoride in drinking water can cause mottling of the teeth (fluorosis) and an exposure of 1.7 ppm will produce mottling in 30–50 % of patients.[25]

See also

References

  1. ↑ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 5.194. ISBN 1439855110.
  2. ↑ Lewis, R.J. Sax's Dangerous Properties of Industrial Materials. 10th ed. Volumes 1–3 New York, NY: John Wiley & Sons Inc., 1999., p. 3248
  3. ↑ 3.0 3.1 Sigma-Aldrich Co., Sodium Fluoride. Retrieved on 2015-03-17.
  4. ↑ Martel, B.; Cassidy, K. (2004), Chemical Risk Analysis: A Practical Handbook, Butterworth–Heinemann, p. 363, ISBN 1-903996-65-1
  5. ↑ "NIOSH Pocket Guide to Chemical Hazards #0563". National Institute for Occupational Safety and Health (NIOSH).
  6. ↑ Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, pp. 313 and 755, ISBN 9781405881180. According to this source, an alternative pronunciation of the second word is /ˈflɔraɪd/ and, in the UK, also /ˈfluː.əraɪd/.
  7. ↑ Wells, A.F. (1984), Structural Inorganic Chemistry, Oxford: Clarendon Press, ISBN 0-19-855370-6
  8. ↑ "Chemical and physical information", Toxicological profile for fluorides, hydrogen fluoride, and fluorine (PDF), Agency for Toxic Substances and Disease Registry (ATDSR), September 2003, p. 187, retrieved 2008-11-01
  9. ↑ Mineral Handbook (PDF) (version 1), Mineral Data Publishing, 2005.
  10. ↑ 10.0 10.1 10.2 Aigueperse, Jean; Paul Mollard, Didier Devilliers, Marius Chemla, Robert Faron, Renée Romano, Jean Pierre Cuer (2005), "Fluorine Compounds, Inorganic", in Ullmann, Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a11_307
  11. ↑ Wood, Alastair J.J.; Eastell, Richard (12 March 1998). "Treatment of Postmenopausal Osteoporosis". New England Journal of Medicine 338 (11): 736–746. doi:10.1056/NEJM199803123381107.
  12. ↑ Riggs, BL; Hodgson, SF; O'Fallon, WM; Chao, EY; Wahner, HW; Muhs, JM; Cedel, SL; Melton LJ, 3rd (22 March 1990). "Effect of fluoride treatment on the fracture rate in postmenopausal women with osteoporosis.". The New England Journal of Medicine 322 (12): 802–9. doi:10.1056/nejm199003223221203. PMID 2407957.
  13. ↑ Mamelle, N; Meunier, PJ; Dusan, R; Guillaume, M; Martin, JL; Gaucher, A; Prost, A; Zeigler, G; Netter, P (13 August 1988). "Risk-benefit ratio of sodium fluoride treatment in primary vertebral osteoporosis.". Lancet 2 (8607): 361–5. PMID 2899773.
  14. ↑ Kleerekoper, M; Peterson, EL; Nelson, DA; Phillips, E; Schork, MA; Tilley, BC; Parfitt, AM (June 1991). "A randomized trial of sodium fluoride as a treatment for postmenopausal osteoporosis.". Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA 1 (3): 155–61. PMID 1790403.
  15. ↑ Riggs, BL; Hodgson, SF; O'Fallon, WM; Chao, EY; Wahner, HW; Muhs, JM; Cedel, SL; Melton LJ, 3rd (22 March 1990). "Effect of fluoride treatment on the fracture rate in postmenopausal women with osteoporosis.". The New England Journal of Medicine 322 (12): 802–9. doi:10.1056/nejm199003223221203. PMID 2407957.
  16. ↑ Pak, CY; Sakhaee, K; Adams-Huet, B; Piziak, V; Peterson, RD; Poindexter, JR (15 September 1995). "Treatment of postmenopausal osteoporosis with slow-release sodium fluoride. Final report of a randomized controlled trial.". Annals of internal medicine 123 (6): 401–8. doi:10.7326/0003-4819-123-6-199509150-00001. PMID 7639438.
  17. ↑ Blau, Monte; Ganatra, Ramanik; Bender, Merrill A. (January 1972). "18F-fluoride for bone imaging". Seminars in Nuclear Medicine 2 (1): 31–37. doi:10.1016/S0001-2998(72)80005-9.
  18. ↑ Grant, F. D.; Fahey, F. H.; Packard, A. B.; Davis, R. T.; Alavi, A.; Treves, S. T. (12 December 2007). "Skeletal PET with 18F-Fluoride: Applying New Technology to an Old Tracer". Journal of Nuclear Medicine 49 (1): 68–78. doi:10.2967/jnumed.106.037200.
  19. ↑ Bourne, volume editor, Geoffrey H. (1986). Dietary research and guidance in health and disease. Basel: Karger. p. 153. ISBN 3-8055-4341-7.
  20. ↑ Jr, Cornelis Klein, Cornelius S. Hurlbut, (1999). Manual of mineralogy : (after James D. Dana) (21st ed., rev. ed.). New York: J. Wiley. ISBN 0-471-31266-5.
  21. ↑ Selwitz, Robert H; Ismail, Amid I; Pitts, Nigel B (January 2007). "Dental caries". The Lancet 369 (9555): 51–59. doi:10.1016/S0140-6736(07)60031-2. PMID 17208642.
  22. ↑ Division of Oral Health, National Center for Prevention Services, CDC (1993), Fluoridation census 1992 (PDF), retrieved 2008-12-29.
  23. ↑ Halpern, D.F. (2001), "Sodium Fluoride", Encyclopedia of Reagents for Organic Synthesis, John Wiley & Sons, doi:10.1002/047084289X.rs071
  24. ↑ Robert L. Metcalf (2007), "Insect Control", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, p. 9
  25. ↑ 25.0 25.1 Robert Kapp (2005), "Fluorine", Encyclopedia of Toxicology 2 (2nd ed.), Elsevier, pp. 343–346
  26. ↑ 26.0 26.1 Greene Shepherd (2005), "Fluoride", Encyclopedia of Toxicology 2 (2nd ed.), Elsevier, pp. 342–343
  27. ↑ NaF MSDS. hazard.com
  28. ↑ CDC - NIOSH Pocket Guide to Chemical Hazards
  29. ↑ Murray TM, Ste-Marie LG. Prevention and management of osteoporosis: consensus statements from the Scientific Advisory Board of the Osteoporosis Society of Canada. 7. Fluoride therapy for osteoporosis. CMAJ. 1996;155(7):949–54. PMID 8837545.
  30. ↑ National Health and Medical Research Council (Australia). A systematic review of the efficacy and safety of fluoridation [PDF]. 2007. ISBN 1-86496-415-4. Summary: Yeung CA. A systematic review of the efficacy and safety of fluoridation. Evid Based Dent. 2008;9(2):39–43. doi:10.1038/sj.ebd.6400578. PMID 18584000. Lay summary: NHMRC, 2007.