Sodium fluoride

Sodium fluoride

Names
Pronunciation	/ˌsoʊdiəmˈflʊəraɪd/ [1]
IUPAC name Sodium fluoride
Other names Florocid
Identifiers
CAS Number	7681-49-4  Y
ChEBI	CHEBI:28741  Y
ChEMBL	ChEMBL1528  Y
ChemSpider	5045  Y
ECHA InfoCard	100.028.789
EC Number	231-667-8
KEGG	C08142  N
PubChem CID	5235
RTECS number	WB0350000
UNII	8ZYQ1474W7  Y
UN number	1690
CompTox Dashboard (EPA)	DTXSID2020630
InChI InChI=1S/FH.Na/h1H;/q;+1/p-1 Y Key: PUZPDOWCWNUUKD-UHFFFAOYSA-M Y InChI=1/FH.Na/h1H;/q;+1/p-1 Key: PUZPDOWCWNUUKD-REWHXWOFAH
Properties
Chemical formula	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)
Solubility in water	36.4 g/L (0 °C); 40.4 g/L (20 °C); 50.5 g/L (100 °C) [2]
Solubility	slightly soluble in HF, ammonia negligible in alcohol, acetone, SO2, dimethylformamide
Vapor pressure	1 mmHg @ 1077 °C [3]
Acidity (pKa)	3,20 (weak base, see HF)
Magnetic susceptibility (χ)	−16.4·10−6 cm3/mol
Refractive index (nD)	1.3252
Structure
Crystal structure	Cubic
Lattice constant	a = 462 pm
Molecular shape	Octahedral
Thermochemistry
Heat capacity (C)	46.82 J/(mol K)
Std molar entropy (S⦵298)	51.3 J/(mol K)
Std enthalpy of formation (ΔfH⦵298)	-573.6 kJ/mol
Gibbs free energy (ΔfG⦵)	-543.3 kJ/mol
Pharmacology
ATC code	A01AA01 ( WHO ) A12CD01 ( WHO ), V09IX06 ( WHO ) (18F)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H315, H319, H335 [4]
NFPA 704 (fire diamond)	3 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	52–130 mg/kg (oral in rats, mice, rabbits) [5]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 2.5 mg/m3 [6]
REL (Recommended)	TWA 2.5 mg/m3 [6]
IDLH (Immediate danger)	250 mg/m3 (as F) [6]
Safety data sheet (SDS)	[4]
Related compounds
Other anions	Sodium chloride Sodium bromide Sodium iodide Sodium astatide
Other cations	Lithium fluoride Potassium fluoride Rubidium fluoride Caesium fluoride Francium fluoride
Related compounds	TASF reagent
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N  verify  (what is  YN ?) Infobox references

Sodium fluoride (NaF) is an inorganic compound with the formula Na F . It is a colorless or white solid that is readily soluble in water. It is used in trace amounts in the fluoridation of drinking water to prevent tooth decay, and in toothpastes and topical pharmaceuticals for the same purpose. In 2021, it was the 291st most commonly prescribed medication in the United States, with more than 600,000 prescriptions. ^{[7] [8]} It is also used in metallurgy and in medical imaging.

Uses

Sodium fluoride is sold in tablets for cavity prevention

Dental caries

See also: Fluoride therapy and Water fluoridation

Fluoride salts are often added to municipal drinking water (as well as to certain food products in some countries) for the purpose of maintaining dental health. The fluoride enhances the strength of teeth by the formation of fluorapatite, a naturally occurring component of tooth enamel. ^{[9] [10] [11]} Although sodium fluoride is used to fluoridate water and 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 United States. ^[12]

Osteoporosis

Fluoride supplementation has been extensively studied for the treatment of postmenopausal osteoporosis. This supplementation does not appear to be effective; even though sodium fluoride increases bone density, it does not decrease the risk of fractures. ^{[13] [14]}

Medical imaging

In medical imaging, fluorine-18-labelled sodium fluoride (USP, sodium fluoride Na¹⁸F) is one of the oldest tracers used in positron emission tomography (PET), having been in use since the 1960s. ^[15] 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. ^[16] Additionally the annihilation photons produced by decay of ¹⁸F have a high energy of 511 keV compared to the 140 keV photons of ^99mTc. ^[17]

Chemistry

Sodium fluoride has a variety of specialty chemical applications in synthesis and extractive metallurgy. It reacts with electrophilic chlorides including acyl chlorides, sulfur chlorides, and phosphorus chloride. ^[18] 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 to the existence of more effective techniques (e.g. Electrofluorination, Fowler process).

Biology

Sodium fluoride is sometimes added at relatively high concentrations (~20 mM) to protein lysis buffers in order to inhibit endogenous phosphatases and thereby protect phosphorylated protein sites. ^[19] Sodium pyrophosphate and Sodium orthovanadate are also used for this purpose. ^[20]

Other uses

Sodium fluoride is used as a cleaning agent (e.g., as a "laundry sour"). ^[21]

Sodium fluoride can be used in a nuclear molten salt reactor.

Over a century ago,^{[ when? ]} sodium fluoride was used as a stomach poison for plant-feeding insects. ^[22] 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. ^[23]

Safety

See also: Fluoride poisoning

The lethal dose for a 70 kg (154 lb) human is estimated at 5–10 g. ^[21]

Fluorides, particularly aqueous solutions of sodium fluoride, are rapidly and quite extensively absorbed by the human body. ^[24]

Fluorides interfere with electron transport and calcium metabolism. Calcium is essential for maintaining cardiac membrane potentials and in regulating coagulation. High ingestion of fluoride salts or hydrofluoric acid may result in fatal arrhythmias due to profound hypocalcemia. 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. ^[25]

Sodium fluoride is classed as toxic by both inhalation (of dusts or aerosols) and ingestion. ^[26] 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. ^[27]

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 peptic ulcer disease. Slow-release and enteric-coated versions of sodium fluoride do not have significant gastric side effects, and have milder and less frequent complications in the bones. ^[28] 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. ^[29] 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. ^[24]

Chemical structure

Sodium fluoride is an inorganic ionic compound, dissolving in water 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; ^{[30] [31]} its lattice spacing, approximately 462 pm, is smaller than that of sodium chloride (564 pm).

Occurrence

The mineral form of NaF, villiaumite, is moderately rare. It is known from plutonic nepheline syenite rocks. ^[32]

Production

NaF is prepared by neutralizing hydrofluoric acid or hexafluorosilicic acid (H₂SiF₆), both byproducts of the reaction of fluorapatite (Ca₅(PO₄)₃F) from phosphate rock during the production of superphosphate fertilizer. Neutralizing agents include sodium hydroxide and sodium carbonate. Alcohols are sometimes used to precipitate the NaF: ^[21]

HF + NaOH → NaF + H₂O

From solutions containing HF, sodium fluoride precipitates as the bifluoride salt sodium bifluoride (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. ^[21]

See also

• Cryolite
• Fluoride therapy

References

1. Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, pp. 313 and 755, ISBN   978-1-4058-8118-0 . According to this source, an alternative pronunciation of the second word is /ˈflɔːraɪd/ and, in the UK, also /ˈfluːəraɪd/ .
2. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 5.194. ISBN   978-1-4398-5511-9.
3. 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
4. Sigma-Aldrich Co., Sodium Fluoride.
5. Martel, B.; Cassidy, K. (2004), Chemical Risk Analysis: A Practical Handbook, Butterworth–Heinemann, p. 363, ISBN   978-1-903996-65-2
6. NIOSH Pocket Guide to Chemical Hazards. "#0563". National Institute for Occupational Safety and Health (NIOSH).
7. "The Top 300 of 2021". ClinCalc. Archived from the original on 15 January 2024. Retrieved 14 January 2024.
8. "Sodium Fluoride – Drug Usage Statistics". ClinCalc. Retrieved 14 January 2024.
9. Bourne, volume editor, Geoffrey H. (1986). Dietary research and guidance in health and disease. Basel: Karger. p. 153. ISBN   978-3-8055-4341-5.{{cite book}}: |first1= has generic name (help)
10. Klein, Cornelis (1999). Hurlbut, Cornelius S. (ed.). Manual of Mineralogy (after James D. Dana) (21st ed., rev. ed.). New York: J. Wiley. ISBN   978-0-471-31266-6.
11. 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. S2CID   204616785.
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14. Vestergaard, P; Jorgensen, NR; Schwarz, P; Mosekilde, L (March 2008). "Effects of treatment with fluoride on bone mineral density and fracture risk—a meta-analysis". Osteoporosis International. 19 (3): 257–68. doi:10.1007/s00198-007-0437-6. PMID   17701094. S2CID   25890845.
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16. Ordonez, A. A.; DeMarco, V. P.; Klunk, M. H.; Pokkali, S.; Jain, S.K. (October 2015). "Imaging Chronic Tuberculous Lesions Using Sodium [18F]Fluoride Positron Emission Tomography in Mice". Molecular Imaging and Biology. 17 (5): 609–614. doi:10.1007/s11307-015-0836-6. PMC   4561601 . PMID   25750032.
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19. Somerville, Laura L.; Wang, Kuan (1988). "Sarcomere matrix of striated muscle: In vivo phosphorylation of titin and nebulin in mouse diaphragm muscle". Archives of Biochemistry and Biophysics. Elsevier BV. 262 (1): 118–129. doi:10.1016/0003-9861(88)90174-9. ISSN   0003-9861. PMID   3355162.
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