Sodium monofluorophosphate, commonly abbreviated SMFP, 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 chemi ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

Na₂PO₃F. Typical for a

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...

, MFP is odourless, colourless, and water-soluble. This salt is an ingredient in some

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 ...

s.Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in ''Ullmann’s Encyclopedia of Industrial Chemistry'' 2008, Wiley-VCH, Weinheim.

Uses

MFP is best known as an ingredient in some

s.Wolfgang Weinert "Oral Hygiene Products" in ''Ullmann’s Encyclopedia of Industrial Chemistry'' 2000, Wiley-VCH, Weinheim. It functions as a source of

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ...

via the following

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

reaction: :PO₃F²⁻ + OH⁻ → HPO₄²⁻ + F⁻ Fluoride protects tooth enamel from attack by bacteria that cause

dental caries Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...

(cavities). Although developed by a chemist at Procter and Gamble, its use in toothpaste ( Colgate toothpaste and Ultra Brite) was patented by

Colgate-Palmolive Colgate-Palmolive Company is an American multinational consumer products company headquartered on Park Avenue in Midtown Manhattan, New York City. The company specializes in the production, distribution, and provision of household, health ca ...

, as Procter and Gamble was engaged in the marketing of Crest toothpaste (containing stannous fluoride, marketed as "Fluoristan"). In the early 1980s, Crest was reformulated to use MFP, under the trademark "Fluoristat"; today Crest toothpastes use

sodium fluoride Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. ...

or stannous fluoride. Compared to straight fluorides, sodium monofluorophosphate has slightly less aftertaste. MFP is also used in some medications for the treatment of osteoporosis. In 1991, sodium monofluorophosphate was found by Calgon to inhibit the dissolution of

lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

in drinking water when used in concentrations between 0.1 mg/L and 500 mg/L.Peter Meier
Monofluorophosphate History
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Tooth decay

Tooth decay is caused by bacteria naturally present in one's mouth. These bacteria form a sticky, colorless soft film on the teeth called plaque. When foods containing

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ...

s (

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

es and sugars) are eaten, the bacteria that form plaque use the sugar as a form of energy. They also turn it into a glue-like substance that helps them stick to the surface of the tooth. The plaque produces acid, which attacks the enamel.

Chemistry of decay

Tooth enamel consists mostly of calcium hydroxyphosphate, Ca₅(PO₄)₃OH, also known as the mineral

hydroxyapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities ...

. Apatite is a hard, insoluble compound. Acid (H⁺), produced especially after a high-sugar meal, attacks the apatite: :Ca₅(PO₄)₃OH_(s) + H⁺_(aq) → Ca₅(PO₄)₃⁺_(aq) + H₂O_(ℓ)

Chemistry of enamel fluoridation

The degradation of apatite by loss of OH⁻ causes the enamel to dissolve. The process is reversible as saliva supplies back OH⁻ to reform apatite. If fluoride, F⁻, ions are present in saliva,

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, b ...

, Ca₅(PO₄)₃F, also forms. :Ca₅(PO₄)₃⁺_(aq) + F⁻_(aq) → Ca₅(PO₄)₃F_(s) Fluorapatite resists attacks by acids better than apatite itself, so the tooth enamel resists decay better than enamel containing no fluoride.

Preparation and structure

Sodium monofluorophosphate is produced industrially by the reaction of sodium fluoride with sodium metaphosphate: :NaPO₃ + NaF → Na₂PO₃F The process involves scission of a pyrophosphate bond, analogous to hydrolysis. NaMFP can also be prepared by treating tetrasodium pyrophosphate or

disodium phosphate Disodium phosphate (DSP), or disodium hydrogen phosphate, or sodium phosphate dibasic, is the inorganic compound with the formula Na2HPO4. It is one of several sodium phosphates. The salt is known in anhydrous form as well as forms with 2, 7, 8, ...

with hydrogen fluoride. In the laboratory, MFP can be prepared by

of difluorophosphate ions with dilute

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 alkal ...

: :PO₂F₂⁻ + 2 NaOH → Na₂PO₃F + H₂O + F⁻

Structure

The structure of the fluorophosphate anion consists of

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

at the center of a tetrahedron defined by three

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

atoms and one fluorine. Formal representations depict a double bond between one oxygen atom and phosphorus, with single bonds for the other two oxygen atoms and the fluorine. In this very formal depiction, negative charge is localized on the O atoms of the single P-O bonds. MFP is similar to and

isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in th ...

with Na₂ SO₄. The anion has C_3v symmetry.

Discovery and development

Sodium monofluorophosphate was first described in 1929 by the German chemist

Willy Lange Willy or Willie is a masculine, male given name, often a diminutive form of William (given name), William or Wilhelm (name), Wilhelm, and occasionally a nickname. It may refer to: People Given name or nickname * Willie Aames (born 1960), American ...

, who was then with the University of Berlin. His fruitless attempts to prepare the free monofluorophosphoric acid led him to check the stability of its esters. Together with

Gerda von Krüger Gerda is a feminine given name. Notable people with the name include: A *Gerda Ahlm (1869–1956), Swedish-born American painter and art conservator * Gerda Alexander (1908–1994), Danish teacher and therapist *Gerda Antti (born 1929), Swedish ...

, one of his students, Lange thus synthesized

diethyl fluorophosphate In organic chemistry, an ethyl group (abbr. Et) is an alkyl substituent with the formula , derived from ethane (). ''Ethyl'' is used in the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry for a saturated t ...

and some analogs, which proved to be quite toxic, being related to

nerve agent Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...

s. In the 1930s,

Gerhard Schrader Gerhard Schrader (25 February 1903 – 10 April 1990) was a German chemist specializing in the discovery of new insecticides, hoping to make progress in the fight against hunger in the world. Schrader is best known for his accidental discovery of ...

, working for the German company

IG Farben Interessengemeinschaft Farbenindustrie AG (), commonly known as IG Farben (German for 'IG Dyestuffs'), was a German chemical and pharmaceutical conglomerate. Formed in 1925 from a merger of six chemical companies— BASF, Bayer, Hoechst, Agfa ...

, tried to develop synthetic insecticide. His work focused on esters of phosphoric acid and resulted in an accidental discovery of some other nerve agents such as DFP ( diisopropyl fluorophosphate), Tabun,

Soman Soman (or GD, EA 1210, Zoman, PFMP, A-255, systematic name: ''O''-pinacolyl methylphosphonofluoridate) is an extremely toxic chemical substance. It is a nerve agent, interfering with normal functioning of the mammalian nervous system by inhibiti ...

, and

Sarin Sarin (NATO designation GB G-series, "B"">Nerve_agent#G-series.html" ;"title="hort for Nerve agent#G-series">G-series, "B" is an extremely toxic synthetic organophosphorus compound.Procter and Gamble Company. In 1947, he and Ralph Livingston of

Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best known product is Roundup, a glyphosate-based herbicide, developed in the ...

published the preparation of the free fluorophosphoric acids and mentioned the use of some toxic esters of monofluorophosphoric acid (like DFP) in the treatment of

glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye re ...

and

myasthenia gravis Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, ...

. The well known toxicity of these esters led to fears that the simple salts might also be toxic, and such fears precluded any large scale commercial use of the salts. In 1950, under sponsorship of the manufacturer of the compounds, Ozark Chemical Company, the toxicity of sodium monofluorophosphate was studied by

Harold Hodge Harold Carpenter Hodge (1904–1990) was a well-known toxicologist who published close to 300 papers and 5 books. He was the first president of the Society of Toxicology in 1960. He received a BS from Illinois Wesleyan University and a PhD in 1930 ...

at the

University of Rochester The University of Rochester (U of R, UR, or U of Rochester) is a private university, private research university in Rochester, New York. The university grants Undergraduate education, undergraduate and graduate degrees, including Doctorate, do ...

who included anti-cavity testing. In 1967

filed several patents on the use of sodium monofluorophosphate in toothpaste.

Safety

The usual content of MFP in toothpaste is 0.76%. The compound is used in place of sodium fluoride, particularly in children's toothpastes, because it is less acutely toxic, although both have modest toxicities. The in rats is 0.9 g/kg.

References

{{DEFAULTSORT:Sodium Monofluorophosphate Phosphates Fluoro complexes Sodium compounds