Fluoride mobility

Acetone is the only solvent in which the conductance of a fluoride salt has been reported ( 0 = 85.0, XqT = 0.27, l/rF- = 0.74). The low mobility is as expected for a small, highly solvated ion. Data on fluoride mobilities in other solvents would be very useful. 

AEA. 2001k. Fluoride Mobility Report, Report Number 20/3034/13/011 (draft), November 14. Pittsburgh, Pa. AEA Technology Engineering Services, Inc. 

In practice, a single crystal of europium-doped lanthanum fluoride (K,p = 2 X 10" ) responds in a matter of seconds according to (13-4) to fluoride ion activity in solutions containing fluoride from about 1 Af to 10" M. Europium doping increases fluoride mobility by introducing lattice disorder. Hydroxide ion, beginning at about 10" Af, is the principal interference, probably the result of competition due to the low solubility of lanthanum hydroxide. 

Olsen et al. [279] considered the effect of pressure on the relative concentrations of different Eu + sites in CaF2. Their strategy was to use pressure as a thermodynamic variable to alter the equilibrium between the different Eu + defect complexes. In their experiments, they first fixed the pressure on Eu + CaF2 to a value between 0 kbar and 20 kbar and then varied temperature (up to 420°C) in order to dissociate existing defect complexes, induce fluoride mobility, and form a new, pressure dependent equilibrium distribution of defects. In samples treated at 420°C and 11 kbar, they observed an increase in A site concentration, a comparable decrease in 0 site concentration, and decreases in concentration of... 

Electrical Conduction by Proton Jumps. As mentioned in Sec. 24, a hydroxyl ion may be regarded as a doubly charged oxygen ion 0 , containing a proton inside the electronic cloud of the ion, which has the same number of electrons as a fluoride ion. The radius of the hydroxyl ion cannot be very different from that of the fluoride ion. But it will be seen from Table 2 that the mobility of the hydroxyl ion is about four times as great. This arises from the fact that a large part of the mobility is undoubtedly due to proton transfers.1 Consider a water molecule in contact with a hydroxyl ion. If a proton jumps from the molecule to the ion,... 

Infrared spectra and F-NMR spectroscopy showed the presence of IF5 and covalently bonded fluorine. Grafoil turns white upon intercalation with IF, this is reminiscent of graphite fluoride, CFi.ij (1,6). The IF, intercalate also evolves IF5 upon heating, but at much higher temperatures than C/IF5 this has been attributed to the lowered mobility of IF5 in the fluorinated matrix, which may no longer be planar. At 450°C, considerable amounts of fluorocarbons are evolved. 

Since hydrogen ions are six to twelve times more mobile than other cations, there will be a delay between loss of hydrogen ions from solution and migration of glass cations into the aqueous phase. Presumably, this electrical imbalance results in an electric field which acts as a driving force for the migration of cations. Aluminium and fluoride are almost certainly transported as cationic aluminofluoride complexes, AIF and AIFJ, mentioned above. 

Alkad A process for improving the safety of alkylation processes using hydrofluoric acid as the catalyst. A proprietary additive curtails the emission of the acid aerosol that forms in the event of a leak. Based on observation of G. Olah in the early 1990s that liquid polyhydrogen fluoride complexes (of amines such as pyridine) depress the vapor pressure of HF above alkylation mixtures. Developed by UOP and Texaco and operated at Texaco s refinery at El Dorado, TX, since 1994. A competing process is ReVAP, developed by Phillips and Mobil. 

In the pentose series, attack has also been observed to occur mainly from the less-hindered side of the double bond, as in the addition of trifluoro(fluoroxy)methane to di-O-acetyl-D-arabinal. Trifluoromethyl 3,4-di-0-acetyl-2-deoxy-2-fluoro-/3-D-arabinopyranoside and 3,4-di-0-acetyl-2-deoxy-2-fluoro-/J-D-arabinopyranosyl fluoride were obtained,72,74 together with a very small proportion of 3,4-di-0-acetyl-2-deoxy-2-fluoro-a-D-ribopyranosyl fluoride.74 With di-O-acetyl-D-xylal, however, the lyxose derivatives were mainly obtained.72,73 The suggestion has been made73 that the greater conformational mobility of pentopyranoses results in a preponderance of the C d) conformer of the D-lyxose derivatives,72,73 such that F-l and CFsO-l are axially disposed. For further reactions of unsaturated carbohydrates with tri-fluoro(fluoroxy)methane, see Section 11,9. 

The aldol condensation of benzaldehyde with the thioacetamide carbanion (RCHCSNRV), derived from the desilylation of the silyl-thioether with tetra-/i-buty-lammonium fluoride, is stereoselective at—80°C producing the erythro isomer of the p-hydroxy thioamide preferentially (Scheme 6.18, R = Me, erythro threo 95 5) via a conformationally mobile intermediate. However, when R is bulky, a greater amount of the threo isomer is formed. Predictably, as the reaction temperature is raised, so the stereoselectively decreases. This procedure contrasts with the corresponding condensation catalysed by titanium salts, where the complexed intermediate produces the threo isomer [47, 48],... 

FIGURE 19 Analysis of a testmix composed of chloride, nitrate, sulfate, fluoride, phosphate, and propionate with a 30 mM PDC buffer at pH 5.4 (trace A) and with a 30 mM PDC buffer at pH 8.2. At pH 8.2, the mobilities of phosphate and propionate increase and the corrected area for phosphate is twice as high due to the presence of two negative charges compared with one negative charge at pH 5.4 (trace B). 

Fluoride concentration in the urine has been used as a biological indicator of fluoride." Most absorbed fluoride is excreted rapidly in the urine. A portion is stored in bone, but a nearly equal amount is mobilized from bone and excreted. Some storage of fluoride occurs from the ingestion of as little as 3 mg/ day. Evidence from several sources indicates that urinary fluoride concentrations not exceeding 5 mg/1 in preshift samples taken after 2 days off work are not associated with detectable osteosclerosis and that such changes are unlikely at urinary levels of 5-8 mg/1." Preshift urinary fluoride concentration is considered to be a measure of the worker s body (skeletal) burden of fluoride, whereas the postshift sample is taken to be representative of exposure conditions during that work shift. 

Several studies have shown that the fluoride balance can be negative [8]. This occurs when the chronic intake is reduced to the extent that concentrations of fluoride in plasma fall and mobilization of fluoride from calcified tissues proceeds. However, there is no evidence so far from human studies that clinical signs of fluoride deficiency exist no specific clinical or biochemical diagnostic parameters have been related to fluoride deficiency [8,39]. In the present state of knowledge, therefore, negative fluoride balance cannot be used for establishing an Al of fluoride. 

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