Sodium fluoride (NaF) is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistr ...

with the formula . It is used in trace amounts in the

fluoridation Water fluoridation is the controlled adjustment of fluoride to a public water supply solely to reduce tooth decay. Fluoridated water contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding ...

of drinking water, in

toothpaste Toothpaste is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from the teeth, a ...

, in

metallurgy Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the sc ...

, and as a

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...

. It is a colorless or white solid that is readily soluble in water. It is a common source of fluoride in the production of pharmaceuticals and is used to prevent

dental cavities Dental may refer to: * Dental consonant, in phonetics * Dental Records, an independent UK record label * Dentistry, oral medicine * Teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates a ...

. In 2020, it was the 265th most commonly prescribed medication in the United States, with more than 1million prescriptions.

Uses

Dental caries

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 Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, bl ...

, a naturally occurring component of

tooth enamel Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, ...

. Although sodium fluoride is used to fluoridate water and is the standard by which other water-fluoridation compounds are gauged,

hexafluorosilicic acid Hexafluorosilicic acid is an inorganic compound with the chemical formula . Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless. Hexafluo ...

(H₂SiF₆) and its salt sodium hexafluorosilicate (Na₂SiF₆) are more commonly used additives in the United States.

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.

Medical imaging

In medical imaging,

fluorine-18 Fluorine-18 (18F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 96% of the time and electron capture 4% of the time. ...

-labelled sodium fluoride ( USP, sodium fluoride F18) is one of the oldest tracers used in

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, ...

(PET), having been in use since the 1960s. Relative to conventional bone

scintigraphy Scintigraphy (from Latin ''scintilla'', "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally and ...

carried out with

gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...

s or

SPECT Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...

systems, PET offers more sensitivity and spatial resolution. Fluorine-18 has a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

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 Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used Radiopharm ...

-labelled

radiopharmaceutical Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which i ...

s. However fluorine-18 is generally considered to be a superior

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 the 140 keV photons of ^99mTc.

Chemistry

Sodium fluoride has a variety of specialty chemical applications in synthesis and extractive

. It reacts with electrophilic chlorides including

acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

s, sulfur chlorides, and phosphorus chloride. Like other fluorides, sodium fluoride finds use in

desilylation Silylation is the introduction of one or more (usually) substituted silyl groups (R3Si) to a molecule. The process is the basis of organosilicon chemistry. Of organic compounds Alcohols, carboxylic acids, amines, thiols, and phosphates can be sily ...

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. Sodium fluoride can be used to produce

fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...

s 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 Electrochemical fluorination (ECF), or electrofluorination, is a foundational organofluorine chemistry method for the preparation of fluorocarbon-based organofluorine compounds.G. Siegemund, W. Schwertfeger, A. Feiring, B. Smart, F. Behr, H. Vogel, ...

, Fowler process).

Other uses

Sodium fluoride is used as a cleaning agent (e.g., as a "

laundry sour A laundry sour is a chemical added to clothing during the final rinse cycle of a washing machine to lower the pH of the water and to assist with the removal of detergents and rust stains. Most such sours are fluoride-based, including ammonium sili ...

"). Sodium fluoride can be used in a nuclear

molten salt reactor A molten salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a molten salt mixture. Only two MSRs have ever operated, both research reactors in the United States. The 1950's A ...

. Over a century ago, sodium fluoride was 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 Phosphopyruvate hydratase, usually known as enolase, is a metalloenzyme () that catalyses the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP), the ninth and penultimate step of glycolysis. The chemical reaction is: :2-ph ...

that require Mg²⁺ as a prosthetic group. Thus, fluoride poisoning prevents phosphate transfer in

oxidative metabolism Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

Safety

The lethal dose for a 70 kg (154 lb) human is estimated at 5–10 g. Fluorides, particularly aqueous solutions of sodium fluoride, are rapidly and quite extensively absorbed by the human body. Fluorides interfere with electron transport and calcium metabolism.

Calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

is essential for maintaining

cardiac The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to ...

membrane potentials and in regulating

coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...

. High ingestion of fluoride salts or hydrofluoric acid may result in fatal

arrhythmias Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

due to profound

hypocalcemia Hypocalcemia is a medical condition characterized by low calcium levels in the blood serum. The normal range of blood calcium is typically between 2.1–2.6 mmol/L (8.8–10.7 mg/dL, 4.3–5.2 mEq/L) while levels less than 2.1 mmo ...

. 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. Sodium fluoride is classed as toxic by both

inhalation Inhalation (or Inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

(of dusts or aerosols) and

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms ingesti ...

. In high enough doses, it has been shown to affect the heart and circulatory system. For occupational exposures, the

Occupational Safety and Health Administration The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...

and the

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...

have established occupational exposure limits at 2.5 mg/m³ over an eight-hour time-weighted average. In the higher doses used to treat

osteoporosis Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone fragility, and consequent increase in fracture risk. It is the most common reason for a broken bone a ...

, 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 Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines i ...

. 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. In the lower doses used for water fluoridation, the only clear adverse effect is

dental fluorosis Dental fluorosis is a common disorder, characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation. It appears as a range of visual changes in enamel causing degrees of intrinsic tooth d ...

, which can alter the appearance of children's teeth during

tooth development Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stage ...

; this is mostly mild and is unlikely to represent any real effect on aesthetic appearance or on public health. Summary: A chronic fluoride ingestion of 1 ppm of fluoride in drinking water can cause

mottling Mottle is a pattern of irregular marks, spots, streaks, blotches or patches of different shades or colours. It is commonly used to describe the surface of plants or the skin of animals. In plants, mottling usually consists of yellowish spots ...

of the teeth (fluorosis) and an exposure of 1.7 ppm will produce mottling in 30%–50% of patients.

Chemical structure

Sodium fluoride is an inorganic

ionic compound In chemistry, an ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding. The compound is neutral overall, but consists of positively charged ions called cations and negatively charged i ...

, 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; its lattice spacing, approximately 462 pm, is somewhat smaller than that of sodium chloride.

Occurrence

The

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

form of NaF,

villiaumite Villiaumite is a rare halide mineral composed of sodium fluoride, Na F. It is very soluble in water and some specimens fluoresce under long and short wave ultraviolet light. It has a Mohs hardness of 2.5 and is usually red, pink, or orange in col ...

, is moderately rare. It is known from plutonic

nepheline syenite Nepheline syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, but dark green varieties are a ...

rocks.

Production

NaF is prepared by neutralizing

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepress ...

(H₂SiF₆), both byproducts of the reaction of fluorapatite (Ca₅(PO₄)₃F) from

phosphate rock Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxi ...

during the production of

superphosphate Triple superphosphate is a component of fertilizer that primarily consists of monocalcium phosphate, Ca(H2PO4)2. Triple superphosphate is obtained by treating phosphate rock with phosphoric acid. Traditional routes for extraction of phosphate ro ...

fertilizer. Neutralizing agents include

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alka ...

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 The bifluoride ion is an inorganic anion with the chemical formula . The anion is colorless. Salts of bifluoride are commonly encountered in the reactions of fluoride salts with hydrofluoric acid. The commercial production of fluorine involves e ...

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.

References

External links

* {{Authority control Fluorides Metal halides Alkali metal fluorides Sodium compounds Dental drugs Rock salt crystal structure