Fluoride and Fluorine, it's the stuff in toothpaste, right? Almost.
For me, fluoride, conjures up images of dozens of little plastic cups with some awful tasting green liquid inside being handed out to seven-year-old children. Back a few decades ago, when I was in grammar school, we were given a fluoride rinse after lunch that tasted as good as fluoride should. As horrible as it was to taste, perhaps it prevented me from getting cavities. I would then and most definitely now rather rinse with a foul tasting fluoride rinse than have to endure a dentist's drill. Fluoride exists as a negative ion (F-)(anion) that can combine with a positive ion (cation) to form stable compounds. This is what you will find it toothpaste and drinking water.
The other one is elemental fluorine, a highly reactive, poisonous, pale yellow gas. It is so reactive that it hardly ever appears in its elemental form in nature. Researchers have been mulling over how to use this element effectively in chemical reactions. Since it is so toxic, ideas about how best to use this element without disturbing the environment is important to practitioners of green chemistry.
Fluoride's derivatives have many other uses than as a mouthwash. Researchers have been making compounds with this element for a long time. The fluoride ion can form various inorganic compounds such as calcium fluoride, magnesium fluoride, and sodium fluoride. All of these are not poisonous to humans or animals, depending on their concentration. There are some significant problems that go along with the production of fluoride compounds but there is also promising research. This may help reduce the negative stigma fluoride compounds carry on its back. Benefits and drawbacks of fluoride have been touted by researchers, environmental activists, and people like me who had to rinse with the stuff.
Named from the Latin word meaning "to flow", fluorine was discovered in 1886. A yellow gas at room temperature, it is the most reactive and electronegative of all the elements. Electronegativity is the tendency of an atom to attract a bonding pair of electrons. It reacts explosively with hydrogen and is reactive with all other elements as well except for nitrogen and oxygen. Fluorine has a tendency to form ions with heavy metals such as iron, aluminum, and manganese. Since it does have an unstable property, fluorine is hardly ever found in its simplest elemental form, but rather as the fluoride ion (F-).
The atom bomb and nuclear projects kick-started the commercial production of fluorine compounds. A large atmospheric source of fluoride is hydrogen fluoride, which is used as a dehydrating agent. Organic fluorides are important in for the drug and agriculture industries representing 30-40% of all agrochemicals and 20% of pharmaceuticals on the market. This 20% include such drugs as Prozac, Paxil, Cipro, and Propulsid. The carbon fluoride bond is the most inert of bonds in organic chemistry and therefore most resistant to degradation. It is this unique property that the element has found its way into refrigerants, plastics, pharmaceuticals, oils, pesticides, etc. Teflon and Gore-Tex are two examples of fluorine atoms at work.
Adding fluorine onto a molecule can literally turn the molecule into a fat loving compound. What does that mean? Well, for drugs such as Prozac and several anti-bacterial agents, that means the drug can stay around longer before the body's metabolism breaks it down.
Researchers have discovered a way to incorporate fluorine as a building block in many of today's medicines. One of the big reasons for this movement is that water would be the only by-product of these reactions. In the past, acids and other toxic wastes would have been generated and would need to be disposed of costing companies time and money and polluting the environment. These fluoroaromatics, as they are called, were born by replacing one of the hydrogen atoms with a fluorine atom. The free hydrogen can now easily bond with oxygen to form water.
Fluorine is poisonous to humans but fluoride is not. It was a discovery of a South African plant in 1943 that would unlock the doors to fluoride research. In trace amounts, it is essential to mammals, strengthening the structure of bones and teeth. Fluoride is also added to water systems for the same purpose. In areas where fluoride is added to drinking water, children are reported to have 70% fewer cavities than non-fluorinated areas. For bone growth, fluoride is the single most important element known today. However, just like anything else, too much of a good thing can become a problem. An excess amount of fluoride can lead to spots on teeth.
Fluorine does have its problems, as environmentalists are quick to point out. Chlorofluorocarbons (CFCs) were identified as being a significant contributor to ozone depletion. Through a process called photolysis, a breakage of one or more covalent bonds occurs (Cl2 ? 2Cl). As CFCs absorb light in the atmosphere, they liberate chlorine radicals (Cl?). These radicals poke holes in the ozone layer allowing harmful ultra-violet rays through the once protective barrier. In 1987, as part of the Montreal Protocol, CFCs were eventually phased out and replaced by hydrofluorocarbons (HCFCs) HCFCs. Used in refrigeration, they are thought to have no significant impact on ozone destruction but are still considered a greenhouse gas.
There is evidence that fluoride compounds can also cause long-term ecological damage. Due to their chemical inertness, resulting from a strong carbon-fluorine bond, these compounds can remain in the environment for a long time. High levels can accumulate in plants, which leads to high levels in the insects, birds, and mammals that eat those plants. In some cases, the levels of fluoride have become toxic. Water pollution from industrial sources and municipal sewage could be one of the causes and remains a concern. This problem has the potential to magnify as it moves up the food chain. Sources of pollution include aluminum smelting and phosphate processing plants. The manufacturing of steel, brick, tile, clay, and glass all contribute to the problem as well as the combustion of coal. On the other hand, the synthesis of fluorinated compounds for agricultural uses has eliminated intermediate reaction pollutants that could find their way to the water supply. High yield fluorinated reactions have allowed researchers to by-pass many of the intermediate steps that were once needed to arrive at a final product.
According to the FDA, fluorine has done more damage to livestock than any other air pollutant. Since some plants can readily uptake fluorine in their tissues, cattle that consume these plants have been affected. Some forage grasses can accumulate 200,000 times the amount of fluorine found in the air. Prolonged ingestion of these contaminated plants can lead to skeletal problems.
It may be possible that a large number of water bodies have become contaminated by fluoride. Water-soluble fluorine can dissolve away from mineral rocks ending up in ground water. In the battle against air pollution, factory scrubbers produce a liquid by-product that contains fluoride and must be disposed of possibly ending up in water supplies. Domestic sewage also plays a role in water pollution due to added fluorine in drinking water. Even with secondary sewage treatments, a significant amount of fluoride still finds its way to streams, lakes, and rivers. What sort of effects do these fluoride levels have on aquatic organisms? Researchers suggest that since oceanic creatures have been exposed to a certain amount of fluorine naturally, they are less likely to be effected than their freshwater counterparts. Freshwater organisms have not been exposed to elevated levels of fluorine (due to the lack of salt water which dissolves mineral rocks containing fluorine) and so they may experience negative physiological effects. Studies have not been conducted to determine what the sub-lethal long-term effects of fluoride are.
The notion of green chemistry is based on highly efficient chemical reactions where little or no waste is produced. This means most of the substrate and reagents should find their way to the final product. The usage of solvents and other compounds found in fluorine reactions should be eliminated or greatly reduced under the green chemistry banner. This minimizes waste disposal issues and environmental concerns. Fluorine is an important player in green chemistry due to it being a very light element, which provides for high efficiency chemical reactions. Fluorine chemists often tote a "less is more" attitude when dealing with fluorine. Fluorine certainly gets a bad rap from many sources but it has also been beneficial to many of us who consume products that were a direct result of fluorine. Clearly, the solution lies somewhere in the middle and the advancements of green chemistry may just provide that solution.
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Tim Fitzpatrick. What You Do and Don't Know About Fluorine and Fluoride. EnvironmentalChemistry.com. Sept. 27, 2006. Accessed on-line: 11/24/2024
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