Fluorinated containers

Florisil Trade name of a magnesium silicate used for chromatography, especially of fluorine-containing compounds. 

PTFE Polyietrafluoroethene. See also fluorine-containing polymers. 

Most fluorine-containing compounds can be reduced to the fluoride ion, F , which can be detected by the tests given below. 

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-alkylated alkyl iodides 931. Q.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779-781]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl aicohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783]. 

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). 

Hydrogen fluoride or compounds that can produce it and fluorine-containing oxidizers should be handled with adequate safety equipment and extreme care by weU-trained personnel. Often the effect of skin exposure is not immediately evident, especially when dilute solutions are handled. Pain may develop several hours later. 

Significant amounts of cryoHte are also recovered from waste material ia the manufacture of aluminum. The carbon lining of the electrolysis ceUs, which may contain 10—30% by weight of cryoHte, is extracted with sodium hydroxide or sodium carbonate solution and the cryoHte precipitated with carbon dioxide (28). Gases from operating ceUs containing HF, CO2, and fluorine-containing dusts may be used for the carbonation (29). 

Manufacture. Boron trifluoride is prepared by the reaction of a boron-containing material and a fluorine-containing substance in the presence of an acid. The traditional method used borax, fluorspar, and sulfuric acid. 

The large amount of fluorine values released from phosphate rock in the manufacture of fertilisers (qv) gives a strong impetus to develop fluorine chemicals production from this source (see Phosphoric acid and the phosphates). Additional incentive comes from the need to control the emission of fluorine-containing gases. Most of the fluorine values are scmbbed out as fluorosiUcic acid, H2SiPg, which has limited useflilness. A procedure to convert fluorosihcic acid to calcium fluoride is available (61). 

Fluorspar occurs in two distinct types of formation in the fluorspar district of southern Illinois and Kentucky in vertical fissure veins and in horizontal bedded replacement deposits. A 61-m bed of sandstone and shale serves as a cap rock for ascending fluorine-containing solutions and gases. Mineralizing solutions come up the faults and form vein ore bodies where the larger faults are plugged by shale. Bedded deposits occur under the thick sandstone and shale roofs. Other elements of value associated with fluorspar ore bodies are zinc, lead, cadmium, silver, germanium, iron, and thorium. Ore has been mined as deep as 300 m in this district. 

Analytical Methods. Fluorite is readily identified by its crystal shape, usually simple cubes or interpenetrating twins, by its prominent octahedral cleavage, its relative softness, and the production of hydrogen fluoride when treated with sulfuric acid, evidenced by etching of glass. The presence of fluorite in ore specimens, or when associated with other fluorine-containing minerals, may be deterrnined by x-ray diffraction. 

Chemicals. Both organic and inorganic fluorine-containing compounds, most of which have highly speciali2ed and valuable properties, are produced from HF. Typically these fluorinated chemicals are relatively complex, sometimes difficult to manufacture, and of high value. These materials include products used as fabric and fiber treatments, herbicide and pharmaceutical intermediates, fluoroelastomers, and fluorinated inert Hquids. Other products include BF, SF, and fluoborates. 

Magnesium is not attacked seriously by dry chlorine [7782-50-5] iodine [7553-56-2] bromine, or fluorine [7782-41 ] gas. However, the presence of water promotes attack. Similarly, sulfur dioxide, ammonia, and fluorine-containing refrigerants do not attack in the absence of water. 

Polyimides containing C—F bonds have been receiving strong attention (96—98). Fluorine-containing polyimides possess lower dielectric constant and dielectric loss because of reduced water absorption and lower electronic polarization of C—F bonds vs the corresponding C—H bonds. Fluorine-containing polyimides are often more soluble and readily processible without sacrificing thermal stabilities. The materials are appHed primarily iu... 

A/-Chloro fatty acid amides have been synthesized from the direct halogenation of the amide in boiling water (28). They are useful as reactive intermediates for further synthesis. Fluorination has also been reported by treating the fatty amide with fluorine-containing acid reagents at 200 °C to reach a fluorinated amide with less reactivity toward fluorocarbon polymers (29). 

Fluorocarbon soHds are rare in defoamer compositions, presumably on account of their cost. SoHd fluorine-containing fatty alcohols and amides are known. The most familiar fluorocarbon soHd is polytetrafluoroethylene [9002-84-0]. Because it is more hydrophobic than siHcone-treated siHca, it might be expected to perform impressively as a defoamer component (14). However, in conventional hydrocarbon oil formulations it works poorly because the particles aggregate strongly together. In lower surface tension fluids such as siHcone and fluorocarbon oils, the powdered polytetrafluoroethylene particles are much better dispersed and the formulation performs weU as a defoamer. 

Two other fluorine-containing diazirines give similar results. Cyanofluorodiazirine (223) and fluoromethoxydiazirine (224) release nitrogen at 100 °C the carbenes formed can be trapped by tetrafluoroethylene to give cyclopropanes (65JHC371). Without a carbene trap alkenes are obtained. 

Polytetrafluoroethylene contains only C—C and C—F bonds. These are both very stable and the polymer is exceptionally inert. A number of other fluorine-containing polymers cU e available which may contain in addition C—H and C—Cl bonds. These are somewhat more reactive and those containing C—H bonds may be cross-linked by peroxides and certain diamines and di-isocyanates. 

The high thermal stability of the carbon-fluorine bond has led to considerable interest in fluorine-containing polymers as heat-resistant plastics and rubbers. The first patents, taken out by IG Farben in 1934, related to polychlorotri-fluoroethylene (PCTFE) (Figure 13.1 (a)), these materials being subsequently manufactured in Germany and the United States. PCTFE has been of limited application and it was the discovery of polytetrafluoroethylene (PTFE) (Figure... 

The inability to process PTFE by conventional thermoplastics techniques has nevertheless led to an extensive search for a melt-processable polymer but with similar chemical, electrical, non-stick and low-friction properties. This has resulted in several useful materials being marketed, including tetrafluoro-ethylene-hexafluoropropylene copolymer, poly(vinylidene fluoride) (Figure 13.1(d)), and, most promisingly, the copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether. Other fluorine-containing plastics include poly(vinyl fluoride) and polymers and copolymers based on CTFE. 

Table 13.1 lists some typical values of PTFE mouldings compared with other fluorine-containing thermoplastics. 

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