Spectrophotometric Determination of Ruthenium with 2,4,6-Tri(T-Pyridyl)-s-Triazine Wallace A. Embryl and Gilbert H. Ayres Depurtment of Chemistry, The Unicersity of Texas at Austin, Austin, Texas 78712 Ruthenium(ll1) reacts ,with 2,4,6-tri(2'-pyridyl)-s-triazine (TPTZ) in water-alcohol solution at pH 2.2 to4.0 to give a red-purple solution having an absorption peak at 510 mp. Full color development requires heating at 87 O C . for one hour; the color is stable for more than 12 hours. The system conforms to Beer's law; optim u m range for measurement at 1.00-cm optical path is about 1 to 4 ppm of ruthenium. Common anions do not interfere; separation from interfering cations is effected by distillation and recovery of ruthenium tetroxide. A reaction ratio of ruthenium-to-TPTZ of 1to-2 is shown by the methods of continuous variations and mole ratio. Isolation and elemental analysis of the picrate and the perchlorate of the cationic complex confirm the 1-to-2 reaction ratio.
THE PREPARATION of 2,4,6-tri(2'-pyridyl)-s-triazine (TPTZ) is
was dissolved in 1 :20 hydrochloric acid; the filtered solution was diluted to known volume with distilled water. Standardization of several aliquots of the solution by the method of Gilchrist and Wichers ( 4 ) and also by a modification of the method of Banks and O'Laughlin (5) gave concordant results averaging 0.503 g of ruthenium per liter. Buffer solutions were prepared by the method of Clark and Lubs (6). All other reagents were ACS reagent grade. Recommended Procedure. Ruthenium solution in aliquots of 10 ml or less was placed in a 25-ml volumetric flask. Three to five ml of pH 2.6 buffer, containing potassium acid phthalate and hydrochloric acid, was added. Five ml of 0.010M TPTZ was added, and if necessary, either water or alcohol was added to adjust the alcohol content between 20 and 5 5 % by volume. The stoppered flask and contents were heated in a water bath at 87 i 1 "C for one hour. The solution was cooled rapidly to room temperature, then diluted to volume with 95% ethanol. Absorbance was measured at 510 mp against a reagent blank prepared similarly. RESULTS
described by Case and Koft ( I ) . A report that this compound could be used as a sensitive reagent for iron ( 2 ) suggested the possibility of color reactions with other transition elements, such as members of the platinum group. Because of the intensity and apparent stability of the color formed with ruthenium, this system was studied in detail. EXPERIMENTAL
Apparatus. Absorbance scanning was made with a Cary Model 14 spectrophotometer. Absorbance measurements at a fixed wavelength were made with a Beckman Model DU quartz spectrophotometer, using matched silica cells of 1.00 cm optical path. A Beckman Model H2 or a Zeromatic pH meter, with saturated calomel-glass electrode system, was used for the pH measurements. Analytical weighings were made with a Mettler Type H5 analytical balance or with a Mettler Type M5 micro balance. Infrared spectra were recorded on Beckman IR-SA and IR-7 spectrophotometers. The constant temperature bath, accurate to &0.5 "C, was constructed according to the directions of Walsh (3). Reagents. The 2,4,6-tri(2'-pyridyl)-s-triazine, obtained from J. T. Baker Chemical Company or from G. Frederick Smith Chemical Company, was used as received. The reagent solution, O.OlOM, was prepared by dissolving 1.562 g of TPTZ in 500 ml of 95% ethanol. Ruthenium(II1) chloride hydrate was obtained from A. D. Mackay, Inc. The solid 1
Calibration, Range, and Sensitivity. The system conforms to Beer's law over the range studied. The optimum concentration range for measurement at 1.00 cm optical path is 1 to 4 ppm of ruthenium. The specific absorptivity is 0.179 ppm-l cm-l, and the molar absorptivity is 1.81 X l o 4 liter mole-' cm-'. Reproducibility. The precision of the method was tested by measuring 30 samples, each containing a final ruthenium concentration of 2.4 ppm, a value in the center of the optimum range. The mean absorbance was 0.431, with a standard deviation of 0.002. Effect of Alcohol. Samples containing 2.4 ppm of ruthenium were developed by the recommended procedure, except that the amount of alcohol was varied. Maximum color development occurred between 20 and 55 ethanol by volume. Effect of pH. The pH was varied by use of appropriate buffers. Maximum absorbance occurred between pH 2.2 and 4.0; the absorbance decreased rapidly on either side of these limits. Effect of Development Time; Color Stability. The absorbance of the solutions increased rapidly during the first several minutes of heating; after 55 minutes the average change in absorbance was only 0.001 absorbance unit per minute. Good reproducibility was obtained by a heating time of one hour. After standing for 18 hours, samples containing 2.4 ppm of ruthenium increased in absorbance by only 0.006 unit (three times the standard deviation in the reproducibility measurements). A one-year-old sample was visually the same color as when first prepared.
Present address, Mobil Chemical, Beaumont,Texas.
(1) F. H. Case, and E. Koft, J. Amer. Chem. SOC., 81,905 (1959). (2) P. F. Collins, H. Diehl, and G. F. Smith, ANAL.CHEM., 31, 1862 (1959). (3) J. M. Walsh, J . Chem. Educ., 44,29 (1967).
(4) R. Gilchrist and E. Wichers, J. Amer. Chem. Soc., 57, 2565 (1935). (5) C. V. Banks and J. W. O'Laughlin, ANAL.CHEM., 29, 1412 (1957). (6) W. M. Clark and H. Lubs, J. Biol. Chem., 25, 479 (1916). VOL. 40, NO. 10, AUGUST 1968
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M O L E F R A C T I O N OF T P T Z
Figure 2. Continuous variations plots
Figure 1. Spectral curves A.
TPTZ reagent. B. Ruthenium-TPTZ complex
Effect of Development Temperature. The rate of color development increased rapidly with temperature up to 86 "C. Above 90 "C evaporation of alcohol, even from a glassstoppered flask, was serious. A temperature of 87 i 1 "C was adopted for the standard procedure. Effect of Reagent Concentration. Samples containing 2.4 ppm of ruthenium were developed by the recommended procedure, except that the concentration of TPTZ was varied. Maximum color development required about a 30-fold molar excess of reagent. Effect of Foreign Ions. Varying amounts of the foreign ions were taken with a fixed amount, 2.4 ppm, of ruthenium, Table I. Effect of Foreign Ions" Foreign Ion Tolerance, P.P.M. Copper(I1) 48 Nickel(I1) 10 Zinc 80 Cobalt(I1) 4.0 Platinum(1V) 2.4 Gold(II1) 6.0 Rhodium(II1) 2.0 Palladium(11) 25 Osmium(111) 2.7 Iridium(1V) 4.1 Iron(I1) 0.0 Iron(111) 0.0 Lead(11) >240 Sodium, potassium, ammonium, bromide, >2400 fluoride, nitrate, perchlorate I 400 Sulfate Citrate 40 Acetate 280 Phosphate 160 Iodide 80 EDTA 2.0 All solutions contained 2.4 ppm of ruthenium. Absorbance measured at 510 mp.
t
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ANALYTICAL CHEMISTRY
A.
Absorbance at 550
mp. E.
Absorbance at 510 mp
and the color was developed and measured in the usual way. The tolerance for a foreign ion was taken as the largest amount that could be present and give an absorbance differing by no more than 0.01 from that produced by ruthenium alone. Tolerances for various ions are shown in Table I. Because the tolerance for some of the ions is rather small, separation of ruthenium is required from solutions containing these ions. Distillation of Ruthenium Tetroxide. The initiaI choice of method was the apparatus and procedure proposed by Banks and O'Laughlin (5). Ruthenium tetroxide was distilled from sulfuric acid-perchloric acid mixture, and absorbed in 0.2M hydrochloric acid containing 5 ml of 5x hydroxylamine hydrochloride. When the recommended procedure of development was applied to the distillate, very little color was produced. With 6M hydrochloric acid as the receiving solution, maximum recovery of ruthenium was 88 per cent. Modification of the apparatus and method resulted in good recovery of ruthenium. The distillation flask, of the Banks and O'Laughlin design, was attached by a 75 O connecting tube to a Vigreaux column packed in ice. The adapter at the bottom of the column carried an inner tube extending to within I or 2 mm of the bottom of the first receiver consisting of a 22-mm tube sealed at the bottom and carrying a side arm leading to a second receiver (25-ml Erlenmeyer flask). The first receiver was connected to the adapter by a 24/40 ground joint. The sample solution was evaporated with sulfuric acid to about 2 ml, then transferred to the distillation flask; 5 ml of sulfuric acid and 2 ml of 70z perchloric acid were added. About 1 ml of perchloric acid was worked into the ground joint of the distilling flask and connecting tube to provide a good seal. The two receivers each contained about 10-15 ml of 6M hydrochloric acid. Distillation was carried out over a period of about 15 minutes, while dry nitrogen gas was passed through the apparatus. The receiving solutions were combined, and all of the apparatus except the distilling flask was washed with 6M hydrochloric acid. The combined
solutions and washings were evaporated to 2-5 ml, then transferred to a 50-mlvolumetric flask and diluted to volume with distilled water. Aliquots of this solution were brought to pH between 2.0 and 3.0 with sodium hydroxide, and the color was then developed by the recommended procedure. Results of several distillation separations are listed in Table 11. STUDY OF THE REACTION
Figure 1, curve B, shows the absorption spectrum of a solution containing 3.2 ppm of ruthenium, developed by the recommended procedure and measured against a distilled water blank; the peak occurs at 510 mp. Curve A is the spectrum of the reagent, recorded against a distilled water blank. A color change from blue toward red as the solution is heated in the development procedure suggests the possibility of more than one complex. Method of Continuous Variations. Application of this method (7-9) was made with a series of solutions of total concentration of ruthenium plus TPTZ = 2.4 X Absorbances were measured at 510 mp and at 550 mp. The continuous variations curves are shown in Figure 2. At 510 mp the curve maximum at 0.65 mole fraction of TPTZ indicates a 2-to-1 mole reaction of TPTZ with ruthenium. For measurements at 550 mp, the curve maximum at 0.5 mole fraction of TPTZ indicates a 1-to-1 reaction ratio. Extensive rounding of the curves is indicative of either extensive dissociation of the complexes, or complexation reactions that have not reached equilibrium when absorbances were measured. Mole Ratio Method. This method (10) was applied to solutions containing ruthenium at a fixed concentration of 1.0 x 10-4M. Absorbances were measured at 510 mp and at 550 mp. Extrapolation of the lower and upper portions of the 510 mp curve showed a significant break at a TFTZ-toruthenium ratio of 2-to-1. The curve of the 550 mp data was too rounded to permit evaluation of any significant change of slope. Ion Exchange Tests. The complex is positively charged, as shown by its retention on cation exchange resins but not on anion exchange resins. Isolation and Analysis of the Complex. Ruthenium(II1) chloride, 0.15 g, was dissolved in 50 ml of water, then adjusted to pH 2.6 with hydrochloric acid, and filtered. TPTZ, 1.5 g, was dissolved in 50 ml of ethanol and added to the ruthenium solution, The mixture was heated at 85-90 "C and evaporated to about 25 ml; an equal volume of water was added and the solution again evaporated to about 25 ml. Upon cooling, excess reagent crystallized from the solution and was recovered for reuse. To the cold solution, 10 g of sodium fluoride was added (to hasten precipitation of excess reagent). After standing for one hour, the excess reagent was filtered off, and recrystallized from ethanol and water, for reuse. A saturated solution of picric acid added to the filtrate produced a brown precipitate which was filtered off, washed with alcohol and then with water, and finally dried at 110 "C for 4 to 6 hours. Calculated for the ruthenium-TFTZ picrate, [RU(C,~H~ZN~)Z](C~HZN~O~)~: C, 46.02 %, H, 2.14%, N, 20.85x, Ru, 7.17x:. Found for two different preparations: (7) P. Job, Ann. Chim., (10) 9,113 (1928). (8) Ibid., (11) 6, 97 (1936). (9) W. C. Vosburgh and G. R. Cooper, J. Amer. Chem. Soc., 63, 437 (1941). (10) J. H. Yoe and A. L. Jones, IND. 111 (1944).
ENG.CHEM.,ANAL.ED., 16,
Table 11. Separation of Ruthenium by Distillation Ruthenium taken Ruthenium found 0.50 mg 0.49 mg l.00mg 1.01 mg 1.50 mg 1.50 mg 4.00 pgn 3.95 pg 10.00 pg 9.89 p g a Contained also 800 ppm each of platinum, rhodium, and palladium, 760 ppm of iridium, and 750 ppm of gold.
(1) C, 46.00%, H, 2.47%, N, 21.00%; (2) C, 46.06%, H , 2.70%, N, 20.87%, Ru, 7.26%. For preparation of the perchlorate derivative, the same procedure was followed through the evaporation of the solution. After cooling, the solution was adjusted to pH 5 by adding ammonium hydroxide. The mixture was chilled in an ice bath for 15 minutes to remove excess reagent, which was filtered off and purified as described above. Addition of 5 g of sodium perchlorate in 20 ml of water produced a reddishbrown precipitate, which was filtered off, washed with water, and dried. The product was purified by two successive extractions with boiling 1,4-dioxane, then dried at 110 "C for four hours. Calculated for ruthenium-TPTZ perchlorate, [R~(CleHI2N&](C104)3: C, 42.23 %, H, 2.36%, N, 16.42z. Found: C,42.47%,H, 2.31%,N, 16.60z. The iodide derivative was prepared in a manner similar to the perchlorate, using potassium iodide instead of sodium perchlorate. Analysis for C, H, and N was somewhat high for the compound [Ru(CI~Hl2N~)2]I~, and was not much improved by a second purification of the precipitate. Collins, Diehl, and Smith ( 2 ) isolated the TPTZ-iron complex as the perchlorate and the iodide salts; analytical data indicated two TPTZ molecules per iron atom. Nonaqueous titrations of the reagent and of the iron complexes indicated that two pyridyl nitrogens and one triazine ring nitrogen of the reagent were coordinated to the iron atom. Similar titrations were attempted with the ruthenium compounds, but the titration curves showed no significant breaks. Infrared spectra of the TPTZ reagent, the ruthenium-TPTZ perchlorate, the ruthenium-TPTZ iodide, and the iron-TPTZ iodide (prepared by the method of Collins, Diehl, and Smith) were obtained. The spectra of the ruthenium and the iron complex iodides are practically identical. The strong band at 1370 cm-l in the reagent has been shifted to slightly lower wave numbers, and the strong band at 1530 cm-1 has been split in both the ruthenium and the iron complexes. The medium-intensity bands at 735 cm-l and 850 cm-l in the reagent are absent in the ruthenium and the iron complexes. On the basis of the elemental analysis data and the comDarison of the infrared spectra of the ruthenium and the iron compounds, the product formed in this study is believed to be a cationic complex of ruthenium(II1) and TPTZ, no oxidation or reduction having occurred, and with the reagent behaving as a tridentate ligand.
RECEIVED for review March 5, 1968. Accepted May 10,1968. Financial support provided by National Science Foundation Grant G P 5454. Condensed from a dissertation submitted by Wallace A. Embry to the Graduate School of The University of Texas at Austin in partial fulfillment of the requirements for the Ph.D. degree, January, 1968. VOL. 40, NO. 10, AUGUST 1968
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