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RECEIVEDfor review December 15,1975. Accepted April 5, 1976. FerroZine is a registered trademark of Hach Chemical Company. It is manufactured under one or more of the following U.S. Patents: 3,709,662; 3,770,735; 3,836,331.
1,2,4,6=Tetraphenylpyridinium Acetate as a New Anion Precipitant Thomas C. Chadwick Union Sugar Division/Consolidated Foods Corporation, Santa Maria, Calif. 93454
lI2,4,6-Tetraphenylpyridinium acetate, a new gravimetric reagent for large Ions such as perrhenate and perchlorate, is prepared in >95 YO yield by reacting lI3,5-triphenyl-2-penten-lI5-dione with aniline in glacial acetic acid. The compound quantitativelyprecipitatesC104- from aqueous solution. In 1.0 M aqueous ammonia, the reagent quantitatively preclpltates Reo4- in the presence of -16-fold excess of MOO^^- or -26-fold excess of W042-. At each concentration for the C104- determination, the relative error of the mean was 99.9% pure) and potassium molybdate were generous gifts of The S.W. Shattuck Chemical Co., Inc., Denver, Colo. Elemental analyses were performed by Galbraith Laboratories, Inc., Knoxville, Tenn. Preparation of 2,4,6-Triphenylpyrylium Bisulfate. The salt was prepared from sulfuric acid, acetophenone, and benzaldehyde (5). Preparation of 1,3,5-Triphenyl-2-penten-l,5-dione. This diketone was prepared from 2,4,6-triphenylpyrylium bisulfate (5). Preparation of 1,2,4,6-TetraphenylpyridiniumAcetate. In a typical preparation, 1,3,5-triphenyl-2-penten-1,5-dione (5.91 g, 18.1 mmol) was mixed with aniline (1.76 g, 18.7 mmol) to form a paste. The paste was then moistened with 120.7 mmol of glacial acetic acid and
heated on a steam bath for 1h. After heating, 20 ml of distilled water were added and the mixture was stirred rapidly while 2 N NaOH was added dropwise. Addition of the NaOH was discontinued after the indicated pH (glass electrode) reached 7.0. The solution was then diluted with water to 181ml. Decolorization with 0.5 g of activated carbon and filtration through Whatman 42 filter paper completed the procedure. Yields, measured by precipitation and weighing of the perchlorate salt, generally were >95%. The shelf life of the reagent, stored in a brown bottle at room temperature, exceeds 14 months. Preparation of 1,2,4,6-TetraphenylpyridiniumPerchlorate. The salt was prepared by the procedure for the determination of uerchlorate: mp 276277 OC, lit. 260 OC (7). Anal. Calcd for C29H22NelO4: C, 71.97; H, 4.58. Found: C. 71.71: H. 4.56. Preparation of 1,2,4,6- Tetraphenylpyridinium Perrhenate. The salt was prepared by the procedure used for the determination of perrhenate: mp 301-303.5 OC. Anal. Calcd for CzgH22NRe04: C, 54.87; H, 3.49. Found: C, 54.65; H, 3.60. Procedure. Gravimetric Determination of Perchlorate. For a typical determination, a 5-10 ml aliquot of c104- solution was transferred to a 150-ml beaker along with 80 ml of distilled water and 0.59 g of NaCl. TPPA solution (0.1 M) was added, with constant stirring, to provide a 10%excess of precipitant. The mixture was allowed to stand for 5 h prior to collection of the precipitate on a fritted glass crucible. The precipitate was washed with a saturated solution perchlorate and dried at 110 "C for of 1,2,4,6-tetraphenylpyridinium 1h prior to weighing. The gravimetric factor for perchlorate anion weighed as 1,2,4,6-tetraphenylpyridiniumperchlorate is 0.2055. Gravimetric Determination of Perrhenate in the Presence of Excess Molybdate or Tungstate. In a typical determination, an aliquot of solution containing 20 mg of Re@- was mixed with an aliquot of solution containing up to 338 mg of Mood2- or 546 mg of W0d2- in a beaker with 6.0 ml of concentrated aqueous ammonia and sufficient water to bring the total volume to 97 ml. Sodium chloride (600 mg) was then added and the Re&- precipitated by addition of 3.5 ml of 0.05 M TPPA solution. After 5 h, the precipitate was collected on a fritted glass crucible, washed with 25 ml of saturated 1,2,4,6-tetraphenylpyridinium perrhenate solution or a dilute solution of TPPA, three 25-ml portions of ice water, and dried at 110 "C for 1 h. The gravimetric factor for perrhenate anion weighed as 1,2,4,6-tetraphenylpyridinium perrhenate is 0.3942. Estimation of Solubilities of Various Pyridinium Salts. The solubility products for the perchlorate, tetrafluoroborate, tetrachloroaurate(III), and hexachloroplatinate(1V) salts were estimated by the method of Loach (8). The solubility of the perrhenate salt was determined by equilibrating the solid perrhenate salt for 191 h with aqueous solutions containing 1.00 M NH3 and either 0.00,0.05, or 0.10 M NaCl and then measuring the perrhenate concentration in the aqueous phase spectrophotometrically. The spectrophotometric method was modified from the one described by Kenna (9). ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
1201
Table I. Analytical Results-Perchlorate No. of runs 6 6
6 6
Taken” (mg) 78.45 39.39 23.52 7.83
Determination
Found (mg, mean)
Re1 std dev, %
78.43 39.37 23.53 7.84
0.06 0.20 0.15 0.27
Weights refer to calculated anions weights, not whole-salt weights. a
Table 11. Analytical Results-Perrhenate
Temp, OC
Salt c104BF4-
Ad&PtCl62Reo4- in 1.00 M
20 20 20 20
KSP
x 10-8
