APPLICATIONS T h e high-molecular weight amines are excellent extractants for cadmium from iodide solutions. Because they can be diluted with relatively inert solvents, they are safer than the ethers and alcohols currently used. The quaternary amine, Aliquat 336-S, is especially attractive for the extraction of cadmium from alkaline as well as acidic solution. The amine-iodide system is of particular value to the environmental analyst because it offers a simple, rapid cadmium concentration method from aqueous solutions containing very small amounts of the element. This suggests that the organic solution can be used directly in flame photometric determinations, in which one can ben-
efit from both the solvent concentration effect and solvent enhanced sensitivity for cadmium. By taking advantage of the selective stripping technique described, the analytical chemist can separate cadmium from mercury in a simple, rapid manner.
ACKNOWLEDGMENT The authors gratefully acknowledge the assistance of H. A. Parker and W. R. Laing for some of the analyses. Received for review October 2, 1972. Accepted November 22, 1972. Research sponsored by the U. S. Atomic Energy Commission under contract with Southern University and Union Carbide Corporation.
2,4,6-Triphenylpyrylium Chloride. A New Organic Analytical Reagent for the Determination of Certain Anions Thomas C. Chadwick Union Sugar Division/Consolidated Foods Corp., Santa Maria, Calif. 93454
Nitron ( I ) , tetraphenylarsonium (2, 3 ) , -phosphonium, and -stibonium chlorides, methylene blue ( 4 ) , and tetran-pentylammonium bromide ( 5 ) have all been used as precipitants for gravimetric or volumetric determinations of various anions. More specifically, nitron and tetraphenylarsonium chloride have been used to determine tetrafluoroborate (6, 7 ) , perchlorate (8, 9 ) , and hexafluorophosphate (10, 11) gravimetrically and volumetrically, and tetraphenylarsonium, -phosphonium, and -stibonium chlorides have been used for the volumetric determination of chloro complexes of mercury, tin, cadmium, and zinc (12, 13). A brief survey of the literature disclosed a wealth of information regarding water-insoluble salts of pyrylium cations and anions of the type listed above ( 1 4 ) . In spite of this extensive body of information, little use has been made of water-soluble pyrylium salts as precipitants for anion analysis (15). It appeared likely that some readily synthesized, water-soluble pyrylium salt would be useful as a n organic precipitant for anions. During the course of this work, a simple synthesis 3f water-soluble 2,4,6-triphenylpyrylium chloride ( T P C ) was ( 1 ) F. J . Welcher, "Organic Analytical Reagents," Vol. I l l , D. Van Nostrand Company, Inc., New York, N.Y., 1947, p 138.
(2) F. J . Welcher. "Organic Analytical Reagents." Vol. i V , D. Van Nostrand Company, Inc., New York, N . Y . . 1948, p 326. (3) P. W . Carr and J . Jordan, Anal. Chem., 44, 1278 (1972). (4) G . M . Nabar and C. R. Ramachandran, Anal. Chem., 31, 263 (1959). (51 R . G . Dosch,Anal. Chem., 40,829 (1968). H . E. Affsprung and V. S. Archer, Anal. Chem., 36, 2512 (1964). C. A. Lucchesi and D. D. DeFord,Anal. Chem., 29, 1169 (1957). (8) D. J . Glover and J . M. Rosen. Anal. Chem., 37,306 (1965). ( 9 ) K . Kodama, "Methods of Quantitative Inorganic Analysis," Interscience, New York, N . Y . , 1963, pp 122, 456. (10) H . E. Affsprung and V. S. Archer,AnaL Chem., 35,976 (1963). (11) H . E . Affsprungand V . S. Archer, Anal. Chem., 35, 1912 (1963). (12) H. H . Willard and G . M . Smith, Ind. Eng. Chern., Anal. Ed., 11, 269 (1939). (13) H . H . Willard and L. R . Perkins, Anal. Chem., 25, 1634 (1953). (14) K . Dimroth and K. H. Wolf in "Newer Methods of Preparative Organic Chemistry," Vol. I l l , W . Foerst, E d . . Academic Press, New York, N . Y . , 1964, p 3 5 7 . (15) H. A . Potratzand J . M . Rosen.AnaL Chem.. 21, 1276 (1949).
devised, and its behavior with a number of anions was studied. In addition, two representative gravimetric procedures were devised. The first, a direct precipitation of perchlorate ion, and the second, a determination of boric acid by conversion to tetrafluoroboric acid and subsequent precipitation, serve to illustrate the utility of the new reagent.
EXPERIMENTAL R e a g e n t s . All melting points are corrected. All inorganic c h e m icals used were reagent grade. Acetophenone (Aldrich Chemical Company, 1nc.j a n d benzaldehyde (J. T. Baker Chemical Company) were used a s received. Distilled, deionized water was used exclusively. Chalcone (1,3-diphenyl-2-propen-l-onej was synthesized by t h e procedure of H e l m k a m p a n d Johnson ( 1 6 ) . 2,4,6-Triphenylpyrylium perchlorate was synthesized from chalcone a n d acetophenone by t h e procedure of Balaban ( I 7). 1,3,5-Triphenyl-2-penten-l,5-dione ( P s e u d o b a s e ) . 2,4,6-Triphenylpyrylium perchlorate (3.96 grams, 9.7 m m o l ) was mixed with 125 ml of boiling 95% ethanol. T h e mixture was stirred vigorously, a n d a solution of anhydrous sodium acetate (3.21 grams, 39.1 mmol) in 50 ml of boiling distilled water was a d d e d in one portion. T h e solution cleared momentarily b u t after a short t i m e t h e product started t o crystallize. T h e reaction mixture was refrigerated overnight a n d t h e crude product (3.21 grams, 100% yield) was collected. Recrystallization from ethanol gave 2.48 grams (79% yield) of white needles: m p 119-122 "C; lit. 115-1163 C ' (18), 119°C (19). 2,i,&Triphenylpyryliurn Chloride ( T P C ) . I n a typical preparation pseudobase (3.26 grams, 10 mmol) was dissolved in 40 ml of boiling 95% ethanol. After dissolution was complete, 1.6 ml of 37% hydrochloric acid were added with vigorous stirring a n d t h e ethanol was evaporated to give t h e crude chloride in quantitative yield. T h e yellow solid was recrystallized from 30 mi of water to which 11 ml of 37% hydrochloric acid h a d been added. Drying to constant weight at 110 "C yielded 3.28 grams (96%) of pure 2,4,6triphenylpyrylium chloride: m p 217-220 "C; lit. 217-219 "C ( 2 0 ) . (16) G . K. Heimkamp and H. W. Johnson, "Selected Experiments in Organic Chemistry," W. H. Freeman, San Francisco, Calif., 1964, p 81. (17) A. T. Balaban, C. R. Acad. Sci., Ser. C., 256, 4239 (1963). (18) A . Williams, J . Amer. Chem. SOC.,93, 2733 (1971). (19) J . A. Berson, J. Arner. Chem. SOC.,74, 358 (1952). (20) K . Kanai, M . Umehara, H . Kitane. and K . F u k u i , Nippon Kagaku Zasshi. 84, 432 (1963);Chem. Abstr., 59, 139349 (1963). ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, M A Y 1973
985
Table I. Results of Typical Perchlorate Analyses
Perchlorate ion rng Taken
Found
40.1
39.9 40.4 40.0 79.8 79.8 79.6 120.8 120.6 120.2 160.7 160.8 160.4
80.1
120.2
160.2
Table 11. Results of Typical Boric Acid Analyses
Error rng
-0.5 +0.8 -0.2 -0.4 -0.4 -0.6 +0.5 4-0.3 0.0 +0.3 +0.4 +0.1 Relative error 0.4% -0.2 4-0.3 -0.1 -0.3 -0.3 -0.5 +0.6 +0.4 0.0 +0.5 4-0.6 +0.2
a
The general reaction responsible for precipitate formation is shown below. (1)
X- = C l o d - or BF4Preliminary precipitation tests were performed using 1% solutions of potassium or sodium salts of various a n ions in 0.2N hydrochloric acid and a 2% solution of T P C in 0.2N hydrochloric acid. Similar tests were performed on various metal ions (1%of the appropriate chloride dissolved in 0.6N hydrochloric acid). T P C gave precipitates with iodide, thiocyanate, trichloroacetate, nitrate, perchlorate, tetrafluoroborate, permanganate, dichromate, and ferrocyanide anions and also with the anionic chloro (21) J. A. Van Allen and G. A. Reynolds, J. Org. Chem., 33, 1102 (1969).
986
Found
mg
%
25.0
25.1 25.1 24.6Q 25.0 49.9 50.2 50.2
+0.1 +0.1 -0.4 0.0 0.0 +0.3 4-0.3
+0.4 +0.4 -1.6 0.0 0.0 +0.6 4-0.6
Relative error 0.5%
RESULTS AND DISCUSSION
x- = (CsH5)3C5H20X(s)
Taken
49.9
Preparations of TPC were generally not dried. The moist, recrystallized solid was used directly to prepare TPC stock solutions. Standard perchlorate solution was prepared by dissolving 5.5801 grams of recrystallized potassium perchlorate in 500.0 ml of water. Standard boric acid solution was prepared by dissolving 5.0020 grams of boric acid in 1000.0 ml of water. The precipitant solution was prepared by dissolving sufficient TPC (wet or dry) in 0.2N hydrochloric acid to make a 0.1N solution. Procedure. In a typical analysis an 80-mg perchlorate sample (10.0 ml of standard perchlorate solution) was transferred to a 150-ml beaker and diluted with 30 ml of 0.2N hydrochloric acid. Ten milliliters of TPC solution were then added with rapid stirring and the solution was allowed to stand at room temperature for 0.5 hr. The solution was refrigerated for 3 hr and the precipitate was collected on a fritted glass crucible (fine porosity), washed with three 5-ml portions of dilute hydrochloric acid, and dried at 110 "C for 1.5 hr before weighing. The gravimetric factor for perchlorate weighed as 2,4,6-triphenylpyrylium perchlorate is 0.2433: mp of unrecrystallized perchlorate, 287.5-289.5 "C; mp of perchlorate recrystallized from acetic acid, 289.5-290.5 "C; lit. 293-295 "C ( 2 1 ) . In a typical boron analysis, 25 mg of boric acid (5.0 ml stock solution) were transferred to a Teflon beaker and mixed with 15 ml of 0.2N hydrochloric acid, 8 ml of TPC solution, and 0.3 ml of 48% HF. The solution was allowed to stand 20 hr at room temperature and 3 hr at 0 "C prior to collection of the precipitate in a fritted glass crucible. The precipitate was washed with an icecold, acidified, saturated solution of 2,4,6-triphenylpyrylium tetrafluoroborate and dried at 110 "C for 1.5 hr. The gravimetric factor for boric acid weighed as 2,4,6-triphenylpyrylium tetrafluo. .. . roborate is 0.1561: mp of unrecrystallized tetrafluoroborate, 247249 "C; lit. 252-253°C (21).
(CsH5)3C5Hz0+ +
Error
Boric acid, rng %
ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, MAY 1973
Precipitate washed with ice water
complexes of zinc(II), tin(II), lead(II), cadmium(II), platinum(IV), and gold(II1). Fluoride, bromide, iodate, chlorate, sulfate, a n d oxalate anions and t h e chloro complex of iron(II1) failed to react with T P C under similar conditions. These experiments show that t h e reagent behaves very much like nitron and the tetraphenylarsonium, -phosphonium, and -stibonium chlorides. Perchlorate analyses (Table I) were carried out using only a small (25%) excess of reagent to ensure complete precipitation. The precipitate was dried at 110 "C without any apparent decomposition. Boron analyses (Table 11) were performed using a modification of t h e procedure of Lucchesi and DeFord ( 7 ) . It was found necessary to use a 60% excess of T P C solution to ensure quantitative precipitation. Washing with icecold, acidified water was tried and was found t o yield low results. Washing with a saturated, ice-cold, acidified (0.2N HCl) solution of 2,4,6-triphenylpyrylium tetrafluoroborate yielded satisfactory results in all cases. Care must be taken when working with T P C to see t h a t all solutions are acidified because its hydrolysis is fairly rapid above a p H of 4 ( 1 8 ) . Its use in neutral or basic solution is thus precluded. Solutions of T P C darken when exposed to light for several weeks. This darkening may be avoided by refrigeration or storage in a brown bottle.
CONCLUSIONS Although T P C has essentially t h e same precipitation characteristics as nitron a n d tetraphenylarsonium chloride it offers some advantages over these and other similar reagents. The perchlorate analysis procedure is as accurate as the corresponding procedure using tetraphenylarsonium chloride (a), the T P C procedure for boron determination is considerably more accurate t h a n the corresponding nitron procedure (7), and T P C is easier to synthesize than the latter two reagents. Interferences common t o nitron and tetraphenylarsonium, -phosphonium, and -stibonium chlorides will certainly be shared by TPC. Methods of eliminating these interferences have been described elsewhere ( 1 , 2, 7) and they would undoubtedly apply to procedures using T P C .
ACKNOWLEDGMENT The author wishes to acknowledge t h e assistance of Kristine Chadwick in the preparation of the manuscript. Received for review October 17, 1972. Accepted January 3, 1973. This work was supported in its initial stages by Public Health Service Grant CA-AM 10385. The major portion of this work was generously supported by Union Sugar Division/Consolidated Foods Corporation.
