Fluorination chlorofluorides

At 225—275°C, bromination of the vapor yields bromochloromethanes CCl Br, CCl2Br2, and CClBr. Chloroform reacts with aluminum bromide to form bromoform, CHBr. Chloroform cannot be direcdy fluorinated with elementary flourine fluoroform, CHF, is produced from chloroform by reaction with hydrogen fluoride in the presence of a metallic fluoride catalyst (8). It is also a coproduct of monochlorodifluoromethane from the HF—CHCl reaction over antimony chlorofluoride. Iodine gives a characteristic purple solution in chloroform but does not react even at the boiling point. Iodoform, CHI, may be produced from chloroform by reaction with ethyl iodide in the presence of aluminum chloride however, this is not the route normally used for its preparation. 

Discussion. This method is based upon the precipitation of lead chlorofluoride, in which the chlorine is determined by Volhard s method, and from this result the fluorine content can be calculated. The advantages of the method are, the precipitate is granular, settles readily, and is easily filtered the factor for conversion to fluorine is low the procedure is carried out at pH 3.6-5.6, so that substances which might be co-predpitated, such as phosphates, sulphates, chromates, and carbonates, do not interfere. Aluminium must be entirely absent, since even very small quantities cause low results a similar effect is produced by boron ( >0.05 g), ammonium (>0.5 g), and sodium or potassium ( > 10g) in the presence of about 0.1 g of fluoride. Iron must be removed, but zinc is without effect. Silica does not vitiate the method, but causes difficulties in filtration. 

As previously stated (p. 53) di-(2-chloroethyl) phosphoro-fluoridate can be prepared by the action of phosphorus oxydi-chlorofluoride on ethylene chlorohydrin. The compound can also be prepared by the fluorination of di (2-chloroethyl) phos-phorochloridate, prepared from di-(2-chloroethyl) hydrogen phosphite (XVIII), obtained by the action of phosphorus trichloride on ethylene chlorohydrin. This partial fluorination was effected by means of sodium fluoride, although the yield was not high. The chlorine atoms of the 2-chloroethyl groups were not affected by this procedure, a fact which falls into line with the observations of Saunders and Stacey (p. 12) that ethylene chlorohydrin is not readily fluorinated by sodium fluoride, but only by potassium fluoride under pressure in a rotating autoclave.1... 

In each class the problem may be resolved into two essential parts (i) the breakdown of the organic compound under appropriate conditions to give a quantitative yield of fluoride ions in aqueous solution, and (ii) the determination of the concentration of these fluoride ions. Methods of breaking down the organic compounds were examined and the procedure adopted for the phosphorofluoridate was different from that used for the fluoroacetate series. From both, however, sodium fluoride was obtained as the breakdown product containing all the fluorine present. After numerous preliminary experiments we came to the conclusion that on the macro-scale a very convenient method of determining the quantity of fluoride ions in the products was by precipitation as lead chlorofluoride,2 PbCIF, which was then dissolved in dilute nitric acid and the chloride was determined by the Volhard method and calculated to the equivalent amount of fluorine. We determined carefully the conditions for the quantitative precipitation of lead chlorofluoride. 

Here again the fluorine was determined ultimately by precipitation as lead chlorofluoride, but the breakdown of the organic compound is more difficult than with the phosphorofluoridates. The two2 methods recommended are... 

The desired extent of fluorination of the starting material may dictate the fluorinating agent to be used. For example, fluorine converts silicon tetrachloride to silicon tetra-fluoride, whereas antimony(III) fluoride promotes the reactions which produce the chlorofluorides, SiCl3F, SiCl2F2, and SiCIFs. 

Calcium fluoride has also been used in metathetical reactions. Usually, heat is required to promote reactions of this type. Booth and Dutton4 passed vapors of a volatile halide [phosphorus(V) oxychloride] over a bed of heated calcium fluoride to produce the chlorofluoride and fluoride derivatives. Sodium fluoride, potassium fluoride, titanium (IV) fluoride, and zinc fluoride have been used in similar metathetical fluorination reactions. 

There appears to be only one really satisfactory method for preparing pure germanium(IV) fluoride. This method involves the thermal decomposition of barium hexafluoro-germanate1 in a quartz or Vycor tube, a method analogous to that described for the preparation of silicon tetrafluoride (synthesis 47). Germanium(IV) fluoride has also been produced by the fluorination of germanium(IV) chloride with antimony (III) fluoride 2 however, it is necessary to distill fractionally the mixture of chlorofluorides resulting from the reaction. 

Fluorination of the trimeric chloride with lead fluoride yields mixed derivatives of the tetramer, p4N4F6Cl2 (74) and P4N4F4CI4 (73). Both compounds polymerize under pressure at 300° to rubbers pyrolysis of the high polymer at atmospheric pressure gives the mixed chlorofluorides PaNaF2Cl4 and P3NSF4CI2 (73). 

Another interesting electrogenerated species particularly important for indirect fluorination reaction is the formation [141] of hypervalent iodobenzene chlorofluoride derivatives. The reaction is performed in the presence of F and Cl ions in anhydrous methylene chloride (Scheme 22). With such reagents, the easy (ex-cell) fluorination oigem-dithioethers was achieved in good yield. 

Moissan and Lebeau (1901) produced sulfuryl fluoride by the combination of sulfur dioxide with fluorine (217). Other processes which have been used to produce the gas are (a) the thermal decomposition of barium fluorosulfonate or certain other fluorosulfonates (188, 221, 808), (b) the reaction of sulfur dioxide with chlorine and hydrogen fluoride in the presence of activated charcoal at 400° (11), (c) the reaction of sulfur dioxide and chlorine with potassium or sodium fluoride at 400° (328), (d) the disproportionation of sulfuryl chlorofluoride at 300-400° (328), (e) the reaction of sulfuryl chloride with a mixture of antimony trifluoride and antimony pentachloride at about 250° (86), (f) the reaction of sulfur dioxide with silver difluoride (86), (g) the reaction of thionyl fluoride with oxygen in an electrical discharge (314), (h) electrolysis of a solution of fluorosulfonic acid in hydrogen fluoride (264), ( ) the reaction of fluorine with sodium sulfate, sodium sulfite or sodium thiosulfate (229, 239), (j) the reaction of hydrogen fluoride with sulfuryl chloride (820). 

Petrov, V.A. Krespan, C.G. Smart, B.E. Electrophihc reactions of fluorocarbons under the action of aluminum chlorofluoride, a potent Lewis acid. J. Fluorine Chem. 1996, 77(2), 139-142. 

A sample placed behind a 25 jum copper beam intensity monitor is irradiated for 15-20 min with a 2 mA beam of 25 MeV He. By chemical etching in 6 M nitric acid a 25-50 Asurface layer is removed. The sample is dissolved in 14 M nitric acid to which some sodium fluoride, zinc nitrate and gallium oxide carrier are added. After addition of phosphoric acid, the temperature is raised to 125° and 150 ml of distillate are collected. Gallium oxide is added to the distillate and gallium hydroxide is precipitated and filtered off. Finally, fluorine is precipitated as lead chlorofluoride The precipitate is repeatedly measured with a Ge(Li) detector during a 10 h period to allow the control of the half-life. Afterwards the yield of the chemical separation is determined by activation with an Ac-Be isotopic neutron source using the F(n,a) N reaction. 

Figure 4.11 Sequential exposures of H CI aliquots (2.0 kPa) to aluminium chlorofluoride (ACF). (a) C counts surface + the volume of gas directly above C2 counts an equivalent gas volume (b) is the intercalibrated count from 2- (c) The derived surface count, obtained from Cl - C2(ic). (Reprinted with permission from M. Nickkho-Amiry and J. M. Winfield, J. Fluorine Chem., 128, 344-352 Copyright (2007) Elsevier Ltd.)...

The halocarbon gases such as pentafluoroethane (HFC-125), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) and 2H-heptafluoropropane (HFC-227ea) are manufactured by either vapor phase or liquid phase catalytic fluorination pathways in continuous mode of operation. The successful catalysts for vapor phase fluorination processes are usually chromium (111) oxide (preactivated with HF) and/or aluminum compoimds doped with Lewis acids such as Co, Ni or Zn. Similarly, antimony (V) chlorofluoride (SbCl Fp/HF is preferred as catalyst in liquid phase fluorination of chlorinated starting compounds. Some of the methods practiced for obtaining individual halocarbons are listed here. 

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