Sodium monofluorophosphate

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Sodium monofluorophosphate

Sodium monofluorophosphate (also disodium monofluorophosphate or MFP) is a chemical with the formula Na₂FPO₃. Its molecular weight is 143.95 g/mol. Typical for a salt, MFP is odorless, colourless, and water-soluble. It melts at 625 °C.

Uses of MFP
MFP is best known as an ingredient in toothpaste

Toothpaste

Toothpaste is a paste or gel dentifrice used to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it can aid in the removal of dental plaque and food from the teeth, aid in the elimination and/or masking of halitosis and deliver active ingredients such as fluoride or xylitol to prevent tooth...
s for both humans and animals. It is claimed to protect tooth enamel from attack by bacteria that cause dental caries

Dental caries

Dental caries, also known as tooth decay, is a disease where bacterial processes damage hard tooth structure . These tissues progressively break down, producing dental cavities ....
(cavities).

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Uses of MFP

MFP is best known as an ingredient in toothpaste

Toothpaste

Dental caries

Dental caries, also known as tooth decay, is a disease where bacterial processes damage hard tooth structure . These tissues progressively break down, producing dental cavities ....
(cavities). Though developed by a chemist at Procter and Gamble, its use in toothpaste (Colgate toothpaste

Colgate

Colgate may refer to:...
) was patented by Colgate-Palmolive

Colgate-Palmolive

Colgate-Palmolive Company is an United States diversified multinational corporation focused on the production, distribution and provision of household, health care and personal products, such as soaps, detergents, and oral hygiene products ....
, as Procter and Gamble was engaged in the marketing of Crest toothpaste (containing stannous fluoride

Stannous fluoride

Tin fluoride, also known as stannous fluoride, is the chemical compound with the formula TinFluorine2. This colourless solid is a common ingredient in toothpaste....
, marketed as "Fluoristan"). In the early 1980s, Crest was reformulated to use MFP, under the trademark "Fluoristat."

MFP is also used in some medications for the treatment of osteoporosis

Osteoporosis

Osteoporosis is a disease of bone that leads to an increased risk of bone fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of collagen proteins in bone is altered....
.

In 1991, sodium monofluorophosphate was found by Calgon

Calgon

Calgon is a brand registered trademark of different corporations. The original product consisted of powdered sodium hexametaphosphate , which in water would complex with ambient calcium ion and certain other cations, preventing formation of unwanted salts and interference by those cations with the actions of soap or other detergents....
to inhibit the solubility of lead

Lead

Lead is a main-group Chemical element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metal ....
in drinking water when used in concentrations between 0.1 mg/L and 500 mg/L.

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

Dental plaque

Dental plaque is biofilm that builds up on the teeth. If not removed regularly, it can lead to dental cavities or periodontal problems .The microorganisms that form the biofilm are almost entirely bacteria , with the composition varying by location in the mouth....
. When foods containing carbohydrate

Carbohydrate

Carbohydrates or saccharides are the most abundant of the four major classes of biomolecules. They fill numerous roles in living things, such as the storage and transport of energy and structural components ....
s, (starch

Starch

File:Amylose2.svgFile:Amylopektin Sessel.svgStarch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds....
es, and sugar

Sugar

Sugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many other sources....
s) 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

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
, which attacks the enamel

Tooth enamel

Tooth enamel is the hardest and most highly mineralized substance of the body, and with dentin, cementum, and Pulp is one of the four major tissues which make up the tooth in vertebrates....
.

Chemistry of decay

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

Apatite

Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of Hydroxyl−, Fluorine−, or Chlorine− ions, respectively, in the crystal....
. Apatite is a hard, insoluble compound. Acid (H⁺), produced especially after a high-sugar meal, attack 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

Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca53F . Fluorapatite is a hard crystalline solid....
, 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

MFP is prepared by heating a difluorophosphate solution in dilute sodium hydroxide

Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
.

PO₂F₂^2-_(aq) + 2 NaOH_(aq) ? Na₂PO₃F_(aq) + 2 HF_(aq)

Discovery and development

Sodium monofluorophosphate was first described in 1929 by the German chemist Dr. Willy Lange, 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 Krueger, one of his students, Lange thus synthesized diethyl fluorophosphate and some analogs, which proved to be quite toxic; the first nerve agents were discovered. In the 1930s, Gerhard Schrader

Gerhard Schrader

Dr. Gerhard Schrader was a Germany chemist specializing in the discovery of new insecticides, hoping to make progress in the fight against hunger in the world....
, working for the German company IG Farben

IG Farben

I.G. Farbenindustrie AG was a Germany chemical industry Conglomerate . Its name is taken from Interessen-Gemeinschaft Farbenindustrie AG . The company was formed in 1925 from a number of major companies that had been working together closely since World War I....
, 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 (= di-isopropyl fluorophosphate), Tabun

Tabun (nerve agent)

Tabun or GA is an extremely toxic chemical substance. It is a clear, colorless, and tasteless liquid with a faint fruity odor. It is classified as a nerve agent because it fatally interferes with normal functioning of the mammalian nervous system....
, Soman, and Sarin. In the meantime, Lange, who was married to a Jewish woman, emigrated from Germany to the United States and started work for Procter and Gamble Company. In 1947, he and Ralph Livingston of Monsanto Company published reports on 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

Glaucoma is a group of diseases of the optic nerve involving loss of ganglion cell in a characteristic pattern of optic atrophy. Raised intraocular pressure is a significant risk factor for developing glaucoma ....
and myasthenia gravis

Myasthenia gravis

Myasthenia gravis is a neuromuscular disease leading to fluctuating muscle weakness and fatigue . It is an autoimmunity, in which weakness is caused by circulating antibody that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine....
. 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 C. Hodge at the University of Rochester

University of Rochester

The University of Rochester is a private university, nonsectarian, research university located in Rochester, New York. The university grants undergraduate, graduate, doctoral, and professional degrees through six schools and various interdisciplinary programs....
who included anti-cavity testing. In 1967 Colgate-Palmolive

Colgate-Palmolive

Colgate-Palmolive Company is an United States diversified multinational corporation focused on the production, distribution and provision of household, health care and personal products, such as soaps, detergents, and oral hygiene products ....
filed several patents on the use of sodium monofluorophosphate in toothpaste..

Content and toxicity

The usual content of MFP in toothpaste is 0.76%. It is not used for water fluoridation. Currently accepted research indicates that by using such toothpaste, cavities may be reduced 17-38%. According to a 2005 World Health Organization study the rate of dental decay in Fluoridated vs. Non-Fluoridated countries is "comparable." The does not lend to Fluoridation as a cause of decreased tooth decay.

The compound is not very toxic. (LD₅₀

LD50

In toxicology, the median lethal dose, LD50 , or LCt50 of a toxic substance or radiation is the Dose required to kill half the members of a tested population....
in rats = 0.9 g/kg).

Structure of fluorophosphate

The structure of the fluorophosphate anion consists of phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. The name comes from the and . A Valency nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate minerals....
at the center of a tetrahedron defined by three oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
atoms and one fluorine

Fluorine

Fluorine is the chemical element with the symbol F and atomic number 9. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F2 molecule....
. 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 with Na₂SO₄

Sulfate

In inorganic chemistry, a sulfate is a salt of sulfuric acid....
.