Fluorine preparative methods

The variety of fluoride compounds that exist and the wide spectrum of their preparation methods are related to the properties of fluorine, and above all to fluorine s high electronegativity. Low dissociation energy of the fluorine molecule, F2, relatively high energies of bond formation found in most fluoride compounds, as well as fluorine s strong oxidizing ability lead, in some cases, to spontaneous fluorination. 

One preparative method involves heating triuranium octaoxide, UsOs, with hydrogen fluoride and fluorine. The product hexafluoride is separated and purified by fractional distillation. 

Another preparative method involves converting triuranium octaoxide to uranyl nitrate, U02(N0s)2, by treatment with nitric acid. Uranyl nitrate then is decomposed to uranium trioxide, UO3, which is reduced to the dioxide, UO2, with hydrogen. A fluidized bed of uranium dioxide is treated with hydrogen fluoride to produce uranium tetrafluoride, UF4, which then is treated with fluorine to form hexafluoride. The preparation should be done in copper apparatus. 

The mixed dimerization of polyhalogenated alkenes with both activated and nonactivated alkcncs has been well documented (see Houben-Weyl, Vol. 4/4, p 206) and continues to represent a convenient preparative method for polyhalogenated cyclobutanes. Of the polyhalogenated alkenes, the fluorinated ethenes are the most reactive towards [2 + 2] cycloadditions. The method is, however, limited by the nonstereoselectivity due largely to the formation of 1,4-diradical intermediates and the requirement of high temperatures. The observation of stereochemical equilibration is seen in the cycloaddition products of tetrafluoroethene (1) with (island (Z)-but-2-ene and (Z)-l,2-[2H2]ethene where mixtures of stereoisomeric cyclobutanes are obtained.19-20... 

The production of industrially important perfluoroalkane sulfonic acids is generally accomplished by electrochemical fluorination. This method of preparation remains expensive and proceeds in good yields only for short hydrocarbon chains.30 Recently however, Wakselman and Tordeux have described a chemical method for the preparation of trifluoromethane sulfonic acid.31 The procedure involves reaction of a metal selected from zinc, cadmium, manganese, and aluminum with sulfur dioxide in DMF, followed by the introduction of trifluoromethyl bromide under slight pressure. The intermediate sulfinate is subsequently oxidized by hydrogen peroxide, and then hydrolyzed which leads to formation of the trifluoromethane sulfonic acid. Successful extension of the sulfination process to the modification of PCTFE should result in the formation of a sulfinated polymer which can ultimately be oxidized to give a sulfonic-acid modified polymer. 

Fluorinating Agent Method of Preparation Yield (%) Properties Ref... 

To conclude with the primary electrode characteristics, we describe briefly the DLC electrodes. The data are scarce and partly contradictory, probably due to the differences in film preparation methods. According to Howe [60], even films as thin as 50 nm are quite stable against corrosion. However, in later works [61, 62] such thin films turned permeable for electrolytes. The penetration of the electrolyte to a substrate metal resulted in its corrosion and, ultimately, in film peeling. Thicker films (0.1 to 1 pm) were less subjected to damage. The current-potential curves in supporting electrolytes resemble those for crystalline diamond electrodes (see Figs. 7, 8) the potential window is narrower, however [63], Fluorination of a-C H enhances corrosion resistance of the films significantly [64],... 

The reader is referred to the second chapter Preparative Methods by J. Grannec and L. Lozano in Inorganic Solid Fluorides , edited by P. Hagenmuller [3], for information on chemical syntheses and crystal growth techniques anterior to 1985, and for general instructions in major preparative techniques in the field of inorganic fluorine chemistry. Some excellent reviews of different topics in the field have been published past 1985 [4-9]. The wide synthetic possibilities of super-acidic media are described in T.A. O Donnell s book [10]. Synthetic and characterization methods with emphasis on solid compounds have been summarized in a book edited by A.K. Cheetham and P. Day [11],... 

Other preparative methods include the photochemical reaction between xenon and excess of fluorine in the presence of Nip2 as catalyst, thermal decomposition of XePe in the presence of NaP (this method is also convenient for the preparation of pure fluorine) and the pyrolysis of some XeP+ salts suchasXeP+PtPe orXeP+Pd2p9 at 423 K (equations 3 and 4). 

Before describing the preparation and properties of trifluoroacetate compounds in general, particular consideration will be given to the parent acid. The normal commercial preparation of trifluoroacetic acid is the electrolytic fluorination of acetyl fluoride or chloride 210). Other preparative methods include the oxidation of trifluorotoluidine or other trifluoromethyl aryl derivatives 247) and the hydrolysis of trifluoro-acetylchloride (6). 

The photolysis of fluorinated compounds is not a very common preparative method because of the formation of mixtures of products nevertheless, front a theoretical viewpoint it is an interesting reaction. The photoelimination of ketones has frequently been examined. 

Preparative Methods the title reagent 1 can be prepared by fluorination of the corresponding (+)-2,10-(3,3-dichlorocamphorsultam) using 10% F2/N2 in dry chloroform in the presence of sodium fluoride. ... 

The world s production of elemental fluorine amounted to around 1990 to 17 000 tons per year it is concentrated in North America, Europe, and Japan. This production is exclusively electrochemical, because F2 is the most highly oxidizing stable species known and so it cannot be industrially obtained by the action of another oxidant. To be exact there are chemical reactions, which produce elemental fluorine, like K NiFg + KF —> K3NiF6 + 1/2F2 (at 673 K, [44]). But then it has to be taken into account that elemental fluorine was needed to prepare the fluorine complex of Ni(IV). And the preparation method described in [45] is only of laboratory scale. 

Depending in part on the preparation method, humic substances may be subject to these problems. However, since oxygen is a major constituent of humic substances, it is important to know its true value. As discussed above, careful accounting of the moisture content of the sample is critical. One should also have information on the composition of the ash so that its effect on the oxygen analysis can be considered. If HF has been used to remove ash constituents, the sample should be analyzed for fluorine residues. 

In recent years devices based on liquid crystal displays have become an inseparable part of our daily life. Flat panel LCD-TV, PC monitors, notebook computers, cellular phones, and PDA would not exist without fluorine-containing liquid crystals. The use of fluorinated substructures, supported by computational methods and the development of novel preparative methods, enables targeted design and synthesis of new materials vith a broad range of custom-tailored properties. 

HFC-134a has been found to be especially useful as a substitute for CFC-12 in automobile air conditioners. A fairly direct preparation method is shown in eqs (7) and (8) TCE = trichloroethylene. The reactions shown are typically done separately in several reaction zones. HCFC-133a can be prepared using catalysts such as Cr/Mg [34], Cr203/A1F3 [35], AlCUF [36], Zn/fluorinated alumina [37], and Zn/Cr [38, 39]. 

The best source of information on techniques for the introduction of fluorine into organic compounds and for information on preparative methods is the excellent treatise by Hudlicky (25), Houben-Weyl s Methoden der Organischen Chemie(65), as well as the books of Shephard and Sharts (25) and Chambers (24). More recently, methods for the fluorination of organic molecules have been reviewed by several authors (15,69-75). More... 

W.G. Grot, C.J. Molnar and P.R. Resnick, Preparation method of fluorinated ion exchangeable polymer, Jpn. Pat. JP 61-47843 (examined application). 

Although the fluorination of PuF4 is the most useful preparative method, plutonium hexafluoride can be prepared by a variety of alternative reactions (58) ... 

Modification of this reaction by the addition of hydrocarbon olefin has been found to be a general preparative method for synthesis of partially fluorinated tetrahy-drothiophenes. " ... 

A. Yu. Shagalov and T. I. Belyakov, Preparation Methods, Properties and Use of Fluorine and its Inorganic Compounds , Bibliographic index of Soviet and foreign literature. No. 1, Part 2, Gos. Inst. Prikl. Khim., Leningrad, U.S.S.R., 1975. 

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