1.1- Chlorofluorides

Addition of calcium nitrate solution to a fluoride gives a white precipitate of calcium fluoride, CaFj. If the latter is precipitated slowly, it can be filtered off and weighed to estimate the fluoride. Fluoride can also be determined by the addition of sodium chloride and lead nitrate which precipitate lead chlorofluoride, PbClF. This is filtered off and weighed. 

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. 

Fluoride may be determined by precipitation as lead chlorofluoride, the precipitate being dissolved in dilute nitric acid and, after adjusting the pH to 5-6, the lead is titrated with EDTA using xylenol orange indicator.10... 

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. 

Meanwhile, a washing solution of lead chlorofluoride is prepared as follows. Add a solution of 10 g of lead nitrate in 200 mL of water to 100 mL of a solution containing 1.0 g of sodium fluoride and 2 mL of concentrated hydrochloric acid, mix it thoroughly, and allow the precipitate to settle. Decant the supernatant liquid, wash the precipitate by decantation with five portions of water, each of about 200 mL. Finally add 1 L of water to the precipitate, shake the mixture... 

The concentration of F ions can be measured by adding an excess of lead(II) chloride solution and weighing the lead(II) chlorofluoride (PbCIF) precipitate. Calculate the molarity of F ions in 25.00 mL of a solution that gave a lead chlorofluoride precipitate of mass 0.765 g. 

Figure 9.13 The geometry of some phosphorus chlorofluorides and some phosphorus methyl fluorides in which the larger and less electronegative ligands occupy the equatorial sites.

Tables 3.28-3.30 summarize the geometry, binding energies, and NBO/NRT descriptors for a variety of linear triatomic XYZ- species. These include representatives of the p-p-p orbital motif (such as symmetric trihalides [X3-, X = F, Cl, Br] and the mixed chlorofluorides [FFCl-, C1FC1-, FC1F-, I CICI-]) as well as the p-s-p (FHF-) and s-s-s (HLiH-, HJ) orbital motifs. (Examples of transition metal species manifesting the s-d-s and p-d-p motifs will be considered in Section 4.10.)...

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. 

The estimation of fluoride as lead chlorofluoride, PbClF, was first described by Stark1 and developed by Hoffman and Lundell,2 Hawley, Fischer and Peisker4 and Kapfenberger.5 Hoffman and Lundell determined the correct pH and chloride-ion concentration for the precipitation. The time for complete precipitation and the effect of varying amounts of fluoride on the composition of the precipitate were examined by Hawley, and these factors were reexamined by us in greater detail. 

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... 

Propensity for free-radical polymerization is most marked for thiocarbonyl chlorofluoride (39). Exposure of the monomer to a sunlamp, especially if benzoin methyl ether is present, leads to rather rapid formation of polymer. Monomer... 

In the reaction of bis(trifluoromethyl) telluride with chlorine monofluoridc, the primary chlorofluoride is converted to bis(trifluoromethyl)tellurium(IV) fluoride by interaction with excess chlorine monofluoride.103... 

Trichloro-l,3.5-triazine (cyanuric chloride, 5) can be converted using a sixfold excess of sulfur tetrafluoride at 250 C into 2,4,6-trifluoro-l,3,5-triazine (cyanuric fluoride, 6) with lower proportions of sulfur tetrafluoride, cyanuric chlorofluorides are formed.191... 

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