V O L U M E 28, NO. 3, M A R C H 19.56 .there is a iyide range of values from zero (benzenic unsaturation, in some cases) to a very high one (allylic unsaturation). K i t h test materials containing different types of double bonds, the curve may, vhen the proper medium is used, show charact,eristic breaks such as in curves I1 and 111,Figure 3. Such curves allo\y the quantitative estimation of the different double bonds by comparison with standard curves, which are established by using mixtures containing known amounts of the same constituents. The full advantage of these properties may not be generally appreciated until a reasonably complete and systematic exploration of PS 14 behavior toward unsaturated compounds has been accomplished. Such a task requires access to a considerable number of pure. not commercially available, chemicals.
365 LITERATURE CITED (1) Adams, R., Voorhees, V., Shriner, R. L., “Organic Synthesis,” Collective Vol. I, p. 463, Wiley, New York, 1948. (2) ddkins, H., Billica, H. R., J . Am. Chem. SOC.70, 695 (1948). (3) Ciapetta, F. G., Plank, C. J., “Catalysis,” Vol. 1 , pp. 315-52, ed. by Paul H. Emmet, Reinhold, iYew York, 1954. (4) Feuge, R. P., Ibid., Vol. 3, pp. 413-31. (5) Hurd, C. D., Roe, A. S., Williams, J. W., J . O i g . C h e n . 2, 314 (1937). (6) Martin, R. TV., U. S. Patent 2,207,868 (July 16, 1940). 46, 1683 (1924). (7) Shriner, R. L., ddams, R., J . Am. Chmna. SOC. (8) Twigg, G. H., Rideal, E. K., Trans. Faraday SOC.36, 533-7 (1940). (9) Vandenheuvel, F. -I., ;INAL. CHEM.24, 847 (1952).
RECEIVED for review January 4, 1955.
Accepted December 19, 1955,
Separation of Radioactive Silver-I 11 from Pile-Irradiated Palladium FRED SlClLlO and M. D. PETERSON, Department o f Chemistry, V a n d e r b i l t University, Nashville, Tenn. GUILFORD G. RUDOLPH, Radioisotope Unit, Thayer Veterans Administration Hospital, Nashville,
and
Radioactive silver-111, a 1-m.e.v. beta emitter with a 7.5-day half life, made by neutron irradiation of palladium metal, w-as separated in a remotely controlled, shielded, glass apparatus. The palladium metal was dissolved in aqua regia and 20 mg. of silver carrier as the chloride complex was added. The separation involved precipitation of silver chloride by dilution, dissolving again in ammonium hydroxide, followed by reprecipitation. The product was recovered in ammonium hydroxide solution or, if silver nitrate was desired, by metathesis to silver oxide, which was then dissolved in nitric acid. The yields were greater than 90yc. The products contained less than 1 y of palladium, and no activities other than that of silver-111 have been detected, even after decaying for 10 half lives. The silver-111 content was about 50 mc. in the highest activity product, and tests indicated that the method may be suitable for much larger quantities of silver-111.
P
ALLADIUiU-110, of 0.135 natural abundance, is transformed by sloiv neutron capture (cross section about 0.4 barn) t o r a d i o a d v e palladium-111, which decays with a 22minute half life by 2-m.e.v. beta emission to radioactive silver-111. The silver-111 is a 1-m.e.v. beta emitter wit,h a 7.5-day half life, decaying t o stable cadmium-111. Also, palladium-108 ~ absorpt’ion cross section (natural abundance 0.268, s l o neut’ron ahout 11 barns) forme radioactive palladium-109, a 1-n1.e.v. I,et,a emitter with 13-hour half life n-hich decays t o stable silver109 (3). Griess and Rogers (1) obtained carrier-free silver-111 by electrolysis from dilute palladium solution. Haymond and others , ( 2 ) carried the silver-111 on a mercurous chloride precipitate, and later removed the carrier by evaporation a t 450’ C. Zimen (8)carried the silver-111 on a silver chloride precipitate, reduced the precipitate to silver using hydrogen a t 500” C., and dissolved the silver in nitric acid. Rouser and Hahn ( 4 ) reduced the animonia complex of t,he silver-111 and carrier silver in the palladium solution Tyith vitamin C, and dissolved the metallic silver in nitric acid. Schweit,zer and Nehls (6)utilized a method based .on the formation of radiocolloids in basic solution, and Sunderman and Meinke ( 7 ) exchanged t,he silver-111 from a solution with the silver of a silver chloride film on platinum gauze. I n the work reported here, 1-gram foils of palladium metal,
Tenn.
irradiated in an Oak Ridge Sational Laboratory reactor for a week, were allowed to “cool” for 4 days before processing, after m-hich time the more intense palladium-109 activity had decreased to about the same level as that of the silver-111. The separation was performed by dissolving the palladium foil in aqua regia, adding inactive silver carrier, then concentrated h j drochloric acid to assure complete solution of all the silver as its complex chloride ion. Silver chloride was precipitated by dilution with water, then dissolved in ammonium hydroxide and reprecipitated for further pui ification. T h e silver chloride 1% as dissolved in ammonium hydroxide for the final product However, if silver nitrate v a s desired as the final product, sodium h>droxide was added t o precipitate silver oxide, which v a s then dissolved in nitric acid. T h e silver chloride from the first precipitation always showed the same slight tan discoloration, indicating palladium contamination. Hon-ever, the amount of palladium adsorbed on the precipitate was clearly shonm t o be less than 10 y by dissolving one of the precipitates in 4 ml. of concentrated hldrochloric acid and comparing the color of the solution and its absorption (at the 460-mp absorption band of palladium-h) diochloric acid solutions) n-ith similar solutions containing known amounts of palladium. The palladium decontamination factor for a single precipitation is about lo5, therefore, the palladiuni contamination after reprecipitation should be only a very small fraction of a microgram. S o n e of the reprecipitated silver chloride products showed any t a n discoloration, and a concentrated hydrochloric acid solution of one showed no absorbancy a t 460 mp, under such conditions that the limit of detection n-as about 1 y of palladium. The color of the silver chloride precipitate is therefore a very delicate indication of the palladium contaminatione.g., if the precipitate is white, the palladium content is surely less than a fexv micrograms. No foreign radioactivities have been detected in the products. Gamma spectra were recorded automatically Kith a sodium iodide (Tl) crystal spectrometer, and the spectrum was not changed by further purification. The activity of a product has been folloned for 10 half lives, with no departure from linearity in the log activity us. time curve. The separation procedure was followed using unirradiated palladium and silver carrier containing purified silver-1 10 (2iO-day half life) rrith an activity of about 20 mr. per hour a t 10 em. The activity of all solutions was measured v i t h a Geiger-Muller survey meter, and also by aliquot counting. The yield was greater than 90% in both cases. T h e jield m-as also
366
ANALYTICAL CHEMISTRY
determined from an aliquot of the product by weighing, showing 93 %recovery of the silver initially added. Each 1-gram foil irradiated in the graphite reactor gave about 2 mc. of separated silver-111. Two grams of palladium, irradiated in the low intensity test reactor, gave about 50 mc. of silver111. Separations were made from as much as 5 grams of palladium without any difficulty, which indicates that this procedure should be suitable for a t least O.l-curie, or possibly multicurie quantities of silver-111.
*
APPARATUS
The separations were carried out in glass equipment P O connected that all necessary operations and transfers could be carried out by regulating pressures in the appropriate vessels with a laboratory rotatory pressure and vacuum pump. The glass vessels were mounted in a hood behind adequate shielding, and over a pan of sufficient volume to hold all the liquids used, in case of breakage. The manifold of stopcocks and the pump were outside the shielding. Mirrors and lights were placed over and inside the shielding, so that all operations could be controlled visually. The more important details of the equipment are shown in Figure 1. Similarly numbered openings in the glass vessels are connected together through the corresponding stopcocks with 3 / 1 & ~ h Tygon tubing. Vessel A is a 2-liter Stang-type solution and precipitation vessel (6) with steep sides to minimize precipitate holdup on the walls. A medium-porosity borosilicate fritted disk, 30 mm. in diameter, is sealed in the bottom of A . Below the filter is an electromagnetically operated funnel, which allorw the waste filtrates and washings to be drawn into the 3-liter filtrate receiver, B , and the product solutions to be withdrawn through the product funnel. T h e stopcock on the product line was operated remotely with a rod through a hole in the shield. Each solution in vessel B could be transferred to the 3-liter temporary storage chamber, C, from which i t could then be returned t o vessel A for reprocessing, if desired, or to a more ermanent shielded waste container through tube and stopcock E. he 1-liter trap, D, prevents spray carry-over from going into the sulfuric acid and Ascarite traps used t o protect the pump. All joints and stopcocks were fastened with spring clamps, and a mercury manometer pressure relief valve was used, set to relieve air from the system a t 18 em. of mercury. Reagents were added remotely to reaction vessel A through a tube that could be directed by long tongs. An infrared lamp was focused on vessel A for heating its contents. Liquids could be held or mixed above the fritted disk for any desired length of time by the application of pressure in B. The apparatus was airtight, so that the turning off of all stopcocks connected to B would retain liquid in A .
I;.
PROCEDURE
Each process step was developed and practiced with inactive and tracer materials until it Tas shown to be reliable, and until a thorough familiarity was obtained with each manipulation, including appropriate pressure or vacuum settings on the pump, time and temperature relations, and the like. Complete tracer and “hot” runs were then carried out with careful monitoring, increasing the ratios of irradiated to inactive palladium, to develop appropriate modifications in equipment, shielding, process, and manipulation. The final procedure follows. About 8 ml. of aqua regia are placed in vessel A , and the irradiated palladium foil is then added with tongs. Heat is applied with the infrared lamp until the palladium is dissolved. This will require less than 45 minutes if the solution is heated above 65” C. Evaporation t o dryness should be avoided to prevent formation of difficultly soluble oxides. Five milliliters of concentrated hydrochloric acid are added, followed by the inactive silver carrier in hydrochloric acid (made by quickly adding 10 ml. of concentrated hydrochloric arid to 19 mg. of silver as silver nitrate, dissolved in 1 ml. of water). The solution is thoroughly mixed and diluted t o a volume of 2 liters with water. The solution is then seeded with 1 mg. of silver as silver nitrate in a few drops of water. The mixture is allowed t o digest overnight a t room temperature, and then filtered. The silver chloride precipitate is washed with 1% nitric acid t o avoid peptization, and the walls of vessel A are washed. T h e silver chloride is dissolved in about 3 ml. of concentrated ammonium hydroxide, then reprecipitated as the chloride by addition of a drop or two of hydro-
B
c
Figure 1. Apparatus for separation of silver-111 from palladium chloric acid. The solution is then made acidic n i t h 6 M nitric acid. The silver chloride is again filtered and washed with 1% nitric acid and dissolved in 3 ml. of concentrated ammonium hydroxide for the final product. If silver nitrate is desired as the final product, the silver chloride precipitate, after washing, is dissolved in a minimum amount (less than 1 ml.) of concentrated ammonium hydroxide. One milliliter of 1 N sodium hydroxide is then added and the solution is heated for about 10 minutes t o expel ammonia and to complete the metathesis to silver oxide. The oxide is collected on the filter, washed with water, and then dissolved in the desired amount of nitric acid. The product solution is withdrawn through the product tube. ACKNOWLEDGMENT
This work was carried out in part under a project sponsored by the U. S. Atomic Energy Commission. Appreciation is expressed to R. G. Wymer, E. L. Alexander, and F. L. Boyer for help in preliminary studies and to Thomas Marshall for help in design and fabrication of glassware. LITERATURE CITED
Griess, J. C., Jr., Rogers, L. B., AECD-2299 (1949); (to U. S. Atomic Energy Commission), U. S. Patent 2,612,470 (Sept. 30, 1952). Haymond, H. R., Larson, K. H., Maxwell, R. D., Garrison, W. M., Hamilton, J. G., J . Chem. Phys. 18, .3?1 (1950). Kinsman, S., “Radiological Health Handbook, Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio, 1954. Rouser, G., Hahn, P. F., J . Am. Chem. SOC.74, 2398 (1952). Schweitzer, G. K., Sehls, J. W., Ibid., 74, 6186 (1952). Stang, L. G., Jr. (to U. S. Atomic Energy Commission), U. S. Patent 2,533,149 (Dec. 5, 1950). Sunderman, D. S . , Meinke, W. W., Science 121, 777 (1955). Zimen, K . E., Z . Nuturforsch. 4a, 95 (1949). RECEIVED for review September 13, 1955, Accepted December 27, 1955.
Direct Volumetric Determination of Total Zinc in Mixed Paint Pigments with Ethylenediaminete traacetic AcidCorrection The authors regret an error in the paper “Direct Volumetric Determination of Total Zinc in Mixed Paint Pigments with Ethylenediaminetetraacetic rlcid” [ANAL. CHEM. 27, 2005 (1955)l. It is erroneously stated that the indicator Eriochrome Black T is a magnesium complex of a hydroxylated azo dye. Eriochrome Black T is the sodium salt of l-(l-hydroxy-2naphthylazo)-5-nitro-2-naphthol-4-sulfonicacid. hl. H. SWANN
