S C I E N T I F I C COMMUNICATION
Soh bilities of Tetraphenylstibonium Salts of Inorganic Anions Procedure for Solvent Extraction of Fluoride Ion from Aqueous Medium SIR: Studies on tetraphenylstibonium salts (2-4) reveal -0lubility behavior which indicates possible usefulne-s of these compounds as reagents for inorganic analysis, partic8,ilarly for the determination of fluoride. The starting materid for the preparation of the salts was tetraphenylstibonium hydroxide ( 4 ) , a compound which precipitates when ammonium hydrouide is added to a saturated aqueous tetraphenylstiboniurn bromide ( I , 6) solution. Most of the salts were readily obtained from the hydroxide by treating it with the appropriate arid-. The lesP soluble salts were also prepared by precipitation from a roncentrated tetraphenylstibonium sulfate solution. Composition of the compounds listed in Table I was established bv chemical analysis ( 2 , 4 ) . Solubilities were determined by shaking the compounds with pure solvent a t constant temper :tture rintil saturation as achieved (8, 4 ) . As can be seen by reference to Table I, tetrapheiiy1~tiI)oniiitii sulfate i- highly soluble in water. Kitrate, chloride, broiiiidt., iodide, fluoride, and perchlorate ions, however, form rc,l:ttively inqoluble tetraphenylstibonium salts and may on this account be more or less quantitatively precipitated from aqiicoiin solution by addition of tetraphenylstibonium sulfate. Tetraphenvlstibonium ion thus offers a possible advantage over some other reagents commonly w e d for precipitation of fluoride, in t h a t it may he used in solutions containing sulfate ion The solubility of tetraphenylstibonium fluoride in water, however, is still too high to allow good quantitative recovery of fluoride t)v precipitation
Table I.
Solubilities of Tetraphenj-lstibonium Compounds
The possibility of separating fluoride from sulfate by solvent partition was accordingly investigated. A saturated, aqueous tetraphenylstibonium fluoride solution Tyas shaken with carbori tetrachloride ( a t 31’ C.) until eqriilibrium n-as attained. The ratio of coiii-entratioii of tetraphenylstibonium fluoride in the carbon tetrachloride 1)hatFe to concentration of tetraphenylstibonium fluoride in the water phase, under the conditions specified, was found to I)e 16.5. T h a t sulfate is not extracted to any appreciable rxtent iinder these conditions \vas demonst,rat,ed by experimentp in which sodium siilfate alone and sodium sulfatesodium fliioride mixtiires containing up to 500 times as much dfate as fluoride \r-eIe carried through the extraction procedure. I n these expcrimrntc: the eodium sulfate was dissolved in n-ater. A f e w drops of dilute Piilfiiric acid, 0 to 0.200 mmole of fluoride (as XaF) and 0.29 minole of (CsH;),Sb+(as tetraphenyMibonium sulfate) were added. The final volume in each case was 19 ml. Extraction \vas nindr hy shaking t’he aqueous solution with three 5-ml. portions of carbon tetrachloride. The combined ext,racts were evaporated. The residue \vas weighed, and the fluoride equivalent was calciilated on the assumption that the residue was (CtiH5),St)F. Fluoride recoveries ranged from 97 to 987;. The blank on 1000 mg. of sodium sulfate, treated as above but with no fluoride added, was 0.02 mg. of fluoride. The effect of a niimher of foreign ions on the fluoride extrartion was investigated. Iron( 111) and aluminum(II1) when present in excessive amount inhibited the extraction. Chloride and bromide, which are themselves extracted to some extent, led to high results. I t was shown, however, t h a t 99.27, recovery of fluoride could be obtained if chloride was first removed by precipitation n ith excess silver. LITERATURE CITED
(Grams of solute per 100 grams of solvent) Solvent Compound
HzO (29’) 0.064 1.68 1.20 0.008
1.10 0.005
...
> 60 I‘
Prepared by heating hydroxide a t 110’.
cc14 (31”) 10 3 2 4 1 os 001 0.14
