Fluoride

Fluoride - What is Fluoride?

Fluoride is the reduced form of fluorine. Both organic and inorganic compounds containing the element fluorine are sometimes called fluorides. Fluoride, like other halides, is a monovalent ion (−1 charge).

Its compounds often have properties that are distinct relative to other halides. Structurally, and to some extent chemically, the fluoride ion resembles the hydroxide ion.

Fluorine-containing compounds range from potent toxins such as sarin to life-saving pharmaceuticals such as efavirenz, and from inert materials such as calcium fluoride to the highly reactive sulfur tetrafluoride.

The range of fluorine-containing compounds is considerable as fluorine is capable of forming compounds with all the elements except helium and neon.

Compounds containing fluoride anions and in many cases those containing covalent bonds to fluorine are called fluorides.

Few inorganic fluorides are soluble in water without undergoing significant hydrolysis. Examples of inorganic fluorides include hydrofluoric acid (HF), sodium fluoride (NaF), and uranium hexafluoride (UF6).

In terms of its reactivity, fluoride differs significantly from chloride and other halides, and is more strongly solvated due to its smaller radius/charge ratio.

Its closest chemical relative is hydroxide. The Si-F linkage is one of the strongest single bonds. In contrast, other silyl halides are easily hydrolyzed.

Many fluoride minerals are known, but paramount in commercial importance are fluorite and fluorapatite. Fluoride is found naturally in low concentration in drinking water and foods.

Water with underground sources is more likely to have higher levels of fluoride, whereas the concentration in seawater averages 1.3 parts per million (ppm).

Fresh water supplies generally contain between 0.01–0.3 ppm, while the ocean contains between 1.2 and 1.5 ppm.

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Fluoride Toxicology

Fluoride-containing compounds are so diverse that it is not possible to generalize on their toxicity, which depends on their reactivity and structure, and in the case of salts, their solubility and ability to release fluoride ions.

Soluble fluoride salts, of which NaF is the most common, are mildly toxic but have resulted in both accidental and suicidal deaths from acute poisoning.

The fatal period ranges from 5 min to 12 hours. Hydrogen fluoride is more dangerous than salts such as NaF because it is corrosive and volatile, and can result in fatal exposure through inhalation or upon contact with the skin; calcium gluconate gel is the usual antidote.

In the higher doses used to treat osteoporosis, 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.

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.

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Fluoride Uses

Fluorides are pervasive in modern technology. Hydrofluoric acid is the most important fluoride synthesized. It is principally used in the production of fluorocarbons and aluminium fluorides.

Hydrofluoric acid has a variety of specialized applications, including its ability to dissolve glass.

Organic synthesis

Fluoride reagents are significant in synthetic organic chemistry. Due to the affinity of silicon for fluoride, and the ability of silicon to expand its coordination number, silyl ether protecting groups can be easily removed by the fluoride sources such as sodium fluoride and tetra-n-butylammonium fluoride (TBAF).

Enzyme inhibitors

In biochemistry, fluoride salts are commonly used to inhibit the activity of phosphatases, such as serine/threonine phosphatases.

It may do this by replacing the nucleophilic hydroxyl ion in these enzymes' active sites.

Beryllium fluoride and aluminium fluoride are also used as phosphatase inhibitors, since these compounds are structural mimics of the phosphate group and can act as analogues of the transition state of the reaction.

Inorganic fluorides

Sulfur hexafluoride is an inert, nontoxic insulator that is used in electrical transformers.

Uranium hexafluoride is used in the separation of isotopes of uranium between the fissile isotope U-235 and the non-fissile isotope U-238 in preparation of nuclear reactor fuel and atomic bombs.

The volatility of fluorides of uranium and other elements may also be used for nuclear fuel reprocessing.

Fluoropolymers

Fluoropolymers such as polytetrafluoroethylene, Teflon, are used as chemically inert and biocompatible materials for a variety of applications, including as surgical implants such as coronary bypass grafts, and a replacement for soft tissue in cosmetic and reconstructive surgery.

These compounds are also commonly used as non-stick surfaces in cookware and bakeware, and the fluoropolymer fabric Gore-Tex used in breathable garments for outdoor use.

Cavity prevention

Fluoride-containing compounds are used in topical and systemic fluoride therapy for preventing tooth decay. They are used for water fluoridation and in many products associated with oral hygiene.

Originally, sodium fluoride was used to fluoridate water; however, hexafluorosilicic acid (H2SiF6) and its salt sodium hexafluorosilicate (Na2SiF6) are more commonly used additives, especially in the United States.

The fluoridation of water is known to prevent tooth decay and is considered by the U.S. Centers for Disease Control and Prevention as "one of 10 great public health achievements of the 20th century".

In some countries where large, centralized water systems are uncommon, fluoride is delivered to the populace by fluoridating table salt. Fluoridation of water is not without critics, however.

Biomedical applications

Positron emission tomography is commonly carried out using fluoride-containing pharmaceuticals such as fluorodeoxyglucose, which is labelled with the radioactive isotope fluorine-18 that emits positrons when it decays into 18O.

Numerous drugs contain fluorine including antipsychotics such as fluphenazine, HIV protease inhibitors such as tipranavir, antibiotics such as ofloxacin and trovafloxacin, and anesthetics such as halothane.

Fluorine is incorporated in the drug structures to reduce drug metabolism, as the strong C-F bond resists deactivation in the liver by cytochrome P450 oxidases.

This article is licensed under the Creative Commons Attribution-ShareAlike License. It uses material from the Wikipedia article on "Fluoride" All material adapted used from Wikipedia is available under the terms of the Creative Commons Attribution-ShareAlike License. Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.