Source of fluorine

Fluorine, which does not occur freely in nature except for trace amounts in radioactive materials, is widely found in combination with other elements, accounting for ca 0.065 wt % of the earth s cmst (4). The most important natural source of fluorine for industrial purposes is the mineral fluorspar [14542-23-5] CaF2, which contains about 49% fluorine. Detailed annual reports regarding the worldwide production and reserves of this mineral are available (5). A more complete discussion of the various sources of fluorine-containing minerals is given elsewhere (see Fluorine compounds, inorganic). 

On average, fluorine is about as abundant as chlorine in the accessible surface of the earth including oceans. The continental cmst averages about 650 ppm fluorine. Igneous, metamorphic, and sedimentary rocks all show abundances in the range of 200 to 1000 ppm. As of 1993, fluorspar was still the principal source of fluorine for industry. 

Iodine pentafluoride is an easily storable Hquid source of fluorine having Httie of the hazards associated with other fluorine sources. It is used as a selective fluorinating agent for organic compounds. For example, it adds iodine and fluorine to tetrafluoroethylene in a commercial process to produce a usefiil telomer (124). 

HF is used as a source of fluorine for production of all the various fluorocarbon products. HF reacts in the presence of a suitable catalyst and under the appropriate temperature and pressure conditions with various organic chemicals to yield a family of products. A by-product stream of hydrochloric acid may be co-produced. 

Many different processes using HF as a reactant or source of fluorine are employed in the manufacture of fluorinated chemical derivatives. In many cases the chemistry employed is complex and in some cases proprietary. Electrochemical fluorination techniques and gaseous fluorine derived from HF are used in some of these appHcations. 

There are many known ways to introduce fluorine into organic compounds, but hydrogen fluoride [7664-39-3] HF, is considered to be the most economical source of fluorine for many commercial appHcations. 

Other Sources of Fluorine. M. H. Klaproth discovered that cryolite, the mineral which later came to be used as a flux in the industrial electrolytic production of aluminum, is a fluoride of sodium and aluminum (76). In 1878 S. L. Penfield, in a research consisting of eight analyses of amblygonite, proved that, contrary to the views of Carl Friedrich Rammelsberg, fluorine and hydroxyl can replace each other in the same mineral (155). Traces of fluorine are found in all types of natural water in oceans, lakes, rivers, and springs (156). 

This, of course, may well be the case, however, even with a radical mechanism in which the adsorbed species took up these same orientations one would expect the hydrogen atoms furthest away from the nitrogen, and therefore closest to the electrode, to be replaced first simply by virtue of their proximity to the source of fluorination. 

An amine with labile fluorine atoms, A -(l,l,2,3,3,3-hexafluoropropyl)diethylamine, generated in situ by the interaction of perfluoroprop-l-ene and diethylamine, was found to work well as a source of fluorine in the reactions of 1,3-dithiolanes with 1,3-dibromo-5,5-dimethylhydan-toin or A -iodosuccinimide. The reactions run in dichloromethane at — 78 to — 20 C give gem-difluorides in 50-70% yield.76... 

The fluorination of a suitable precursor by a fluorinating agent of specific activity is a method used to synthesize selectively fluorinated molecules. This has been accomplished by various reagents where the source of fluorine is a carbon-fluorine bond (C —F reagents). 

Halogen exchange reactions, too, are valuable sources of fluorinated pyrimidines, especially 2-, 4-, and 6-fluoro derivatives. Sources of fluoride ion have included hydrogen, sodium, potassium, cesium, antimony, silver fluorides, and sulfur tetrafluoride. All of the reactions required heating. Prepared from nucleophilic fluorination processes have been... 

As indicated in Chapter 1, this book has been designed to be an introduction to fluorine NMR and to serve as a practical handbook for use by organic chemists involved in the synthesis of fluorinated organic compounds, with an emphasis on characterization of lightly fluorinated organic compounds. It is meant to serve as a primary source of fluorine, proton, carbon, and to a more limited extent phosphorous and nitrogen... 

Silica is present in the mineral as an impurity, and it reacts with hydrofluoric acid to yield silicon tetrafluoride, which can be converted to fluorosifi-cic acid, an important source of fluorine. More than half of the phosphoric acid that is produced by the reaction of phosphates with sulfuric acid is converted directly to sodium or ammonium phosphates to be used as fertilizer thus, purity is not a concern. 

Xenon difluoride is able to transfer a fluorine atom to organic molecules without any catalyst, with very reactive organic molecules or at higher temperatures or under photochemical conditions. However, reactions are usually performed in the presence of various types of catalysts, but in some cases a new xenon compound FXeYL is formed (Scheme 1), which can be a source of fluorine atoms, or of a YL or Y group for transfer to an organic molecule. On the other hand, decomposition of the FXeYL molecule results in the desired fluorinated products (FYL, FL or FY). Fluoro-substituted xenon derivatives (FXeYL) can also be further transformed to disubstituted derivatives, which are usually less stable at room temperature, but can also be excellent sources of YL, Y or L groups for transfer to various organic molecules. The next possibility is that xenon difluoride converts an... 

Xenon difluoride appears to be a convenient source of fluorine for the fluorination of diorganyl telluriums3,4. 

Fluorine occurs in nature in the form of the minerals fluorite, CaF2, cryolite, Na3AlF6, and fluoroapatite, Ca5(P04)3F, and one commercial source of natural cryolite is Greenland. Both of the other minerals are widespread in nature, although the major use of fluoroapatite is in the production of fertilizers, not as a primary source of fluorine. Extensive fluorite deposits are found in Southeastern Illinois and Northwestern Kentucky. From the standpoint of fluorine utilization, both cryolite and fluorite are extremely important minerals. Cryolite is used as the electrolyte in the electrochemical production of aluminum from bauxite, and fluorite is used as a flux in making steel. Today, most of the cryolite used is synthetic rather than the naturally occurring mineral. 

The reported solubility product of CaF2 is 10 (Allison and Brown, 1992). The model predicted values for TP and PL 0- to 15-cm soil water extracts between 10 s 29 and 10" 52 with a mean of 10-1046. For the 15- to 30-cm depth, predicted ion-activity product values ranged from 10-8 31 and 10 1311,1 with a mean value of 10 n 02 These results indicate that near the source of fluorine, as soil depth increases, the F precipitates as CaF2 mineral. The soils in the study area are alkaline and also contain sufficient amounts of dissolved Ca2+ (see Tables 13.1 to 13.3). Both alkaline... 

It is clear that Ag(III) in any fluoro ligand environment has a high enough electron affinity to take an electron from Xe and to be an effective source of fluorine atom ligands. 

Falandysz, J., Taniyasu, S., Gulkowska, A., Yamashita, N. Is fish a major source of fluorinated surfactants and repellents in humans living on the Baltic Coast Environ. Sci. TechnoL, 40 748-751 (2006). 

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