April, 1957
ION-EXCHANGE AND SOLVENT-EXTRACTION STUDIES WITH POLONIUM
43 1
ION-EXCHANGE AND SOLVENT-EXTRACTION STUDIES WITH POLONIUM BY J. DANON AND A. A. L. ZAMITH Escola Nacional de Quimica, Rio de Janeiro, Brazil Received September 81, 1966
An investigation has been made of the ion-exchange and solvent-extraction behavior of polonium in hydrochloric and nitric acid media. Adsorption by an anion-exchange resin, Dowex-1, from nitric acid solutions is unusually slow. Reducing agents, which had no effect on anion exchange and solvent extraction in hydrochloric acid solutions, exerted a marked influence on these processes in nitric acid media. The tendency of polonium to form complexes and its oxidation-reduction reactions are discussed.
hydrochloric acid concentrations of 0.05-2.5 M and nitric acid concentrations of 0.1-5.0 M . The initial concentration of polonium was approximately 2X M in each experiment. The following distribution coefficients D (amount of Po in counts per minute per gram of dry resin divided by the amount of Po in counts per minute per ml. of solution) were obtained in hydrochloric acid solutions: 150 a t 0.05 M HC1, 10 a t 0.1M HC1, 1.3 a t 0.2 M HC1 and 4 M ) ; the chlorine addition did not influence by recent research with weighable quantities of the element.6 the D values. The adsorption of polonium by Dowex-1 is Studies with both micro' and macro-quantities8 of polonium indicate that hydrazine reduces polo- qualitatively similar to that of gold(III),'O platnium ( f 4 ) to a lower oxidation state. We found inum(1V)B and other elements which show a genthat reducing agents have practically no influence eral decrease in adsorption with increasing hydroon the adsorption of polonium from hydrochloric chloric acid concentration. On the basis of the acid, although a t low hydrochloric acid concentra- interpretation given by Kraus for the adsorption of tions, hydrazine caused a slight increase in the D elements by anion-exchange resins,6.'0*11one would conclude that a t trace concentrations the negavalues observed with Dowex-1. The adsorption equilibrium was attained both tively charged complexes of polonium are essenin the oxidized and reduced state in approximately tially completely formed a t low hydrochloric acid 2 4 4 8 hours. When some experiments were re- molarities ( tellurium > selenium. Although hydrazine did not influence the anion-exchange behavior of polonium in hydrochloric acid it has been shown that under these conditions polonium is reduced to a low oxidation state.6 Since under this form polonium is strongly adsorbed by the anion-exchange resins a t all the hydrochlorjc acid concentrations investigated, it is plausible to assume that the low oxidation state is also strongly complexed in this acid. The adsorption of Po(IV) by Dowex-1 in nitric acid solution was much slower than that which has been reported for other elements, in nitric acid and hydrochloric acid media. Only a few elements, viz., molybdenum(V1) , tungsten(V1) l6 and less markedly protactinium(V),l7 behave similarly. As these elements have a strong tendency t o hydrolyze under such conditions, the slow adsorption may be related to the presence of hydrolytic polymers in the aqueous phase. l6 Apparently polonium(1V) nitrate, like tellurium(1V) nitrate, f o r m hydrolyzed species even a t high nitric acid concentrations, as was suggested before by F. Joliot. l8 On the basis of the solubility data of polonium nitrate,19 it was concluded that PoO(NO3)3-' ions are formed below 1 M HN03,20 and Po(NO3)?-' are formed a t higher concentrations of this acid. However, the results from ion-migration and cation-exchange studies show that positively charged ions of polonium are present until a t least 5 A4 " 0 3 , indicating that the negatively charged complexes are not completely formed a t these concentrations. It seems that a fraction of these positively charged species are hydrolytic polymers of polonium. I n the cation-exchange experiments the equilibrium was attained, as usually, in a few hours. Presumably the slow step in the anion-exchange process is not the adsorption but the depolymerization of polonium polymers with the formation of negatively charged complexes. Slow depoly(14) R. A. Kraus, G. E. Moore and F. Nelson, J . A m . Chem. Soc., 78, 2692 (1956). (15) U. Schindewolf and C. D. Coryell, R1.I.T. Progress Report, November 1955, p. 16 and February 1956, p. 16. (IO) K. A. Kraus, F. Nelson and G. E. Moore, J . A m . Chem. SOC., 77, 3972 (1955). (17) K. A. Kraus and G. E. Moore, ibid.. 73, 4293 (1950). (18) F. Joliot. J . chirn. phys., 27, 119 (1930). (19) E. Orban, "The Solubility of Polonium Nitrate in Nitric Acid Media," Information Report MLM-973, Mound Laboratory, 1954. (20) The existence of polonyl ions Po0 + 2 in "01 media was previously Ruggested by F. Joliot.18
433
f
;40/ .v
4 20 0
0
2 4 6 8 Molarity of " 0 3 . Fig. 3.-0, organic peroxide; 0 , sulfur dioxide; a, hydrogen peroxide; 0 , hydrazine; 0 ,hydroxylamine.
I
t - 0 1
2
MOLARITY
OF
HNO.,.
Fig. 4.-#, hydrazine, 0.05M; 0, hydrogen peroxide, 0.1M; 0 , sulfur dioxide, 0.05M; X, hydroxylamine, 0.05 M.
merization was observed with plutonium polymers in HN03 media.21 The oxidation-reduction behavior of polonium appears to be influenced by the amount of polonium, by the medium and by the reducing agent. I n agreement with electrochemical studies with trace amounts of polonium in sulfuric and acetic acid medialz2 our solvent-extraction and anion-exchange data suggest that hydrazine, sulfur dioxide, hydrogen peroxide and hydroxylamine reduce polonium( +4) to a lower oxidation state. With macro-amounts of the element in hydrochloric acid solutions, it was found that hydrazine and sulfur dioxide reduce polonium (+4) ; hydroxylamine has no effect on solutions of polonium chlorides, but it reduces polonium( +4) in sulfuric acid and hydrogen peroxide oxidizes polonium(+%) to the f 4 state. Nitric acid or its radiolysis products appears to oxidize macro-amounts of reduced polonium to its normal f 4 statedz3 (21) K. A. Kraua and F. Nelson, "Hydrolytic Behavior of Heavy Elements." Proceedings of the International Conference on Peaceful Uses of Atomic Energy, Vol. 7, p. 245, United Nations, 1956. (22) M. Guillot and M. Haissinsky, Bull. soc. chim., 239 (1935). (23) K. W. Bagnall, personal communication.
434
EDWARD 0. HOLMES, JR.
The failure of hydroxylamine to reduce polonium in hydrochloric acid solution probably is due to the stability of the complex polonium(1V) chlorides. However, the reactions of polonium with hydrogen peroxide seem to be a function of the concentration of the element, since in all media investigated hydrogen peroxide oxidizes macroamounts of polonium( +2) and apparently reduces trace-amounts of polonium( $4). For plutonium (IV) also the reactions with hydrogen peroxide in nitric acid media are different for trace and macroquantities of the element.24 Little can be said about the numerical value of the lower oxidation state of trace-amounts of (24) G. T. Seaborg and J. J. Kats, "The Aatinide Elements," National Nuclear Energy Series, Vol. 14-A,MoGraw-Hill Book Co., New York, N. Y., 1954, p. 279.
Vol. 61
polonium in nitric acid. Although recent research with weighable quantities of the element showed that the reduction of polonium(f4) in hydrochloric and sulfuric acid gives a +2 oxidation state, there is evidence for a +3 state in hydrochloric acid.6 The tendency of reduced polonium to form negatively charged complexes in nitric acid and its extraction by ether under these conditions are properties similar to those of +3 elements such as gold, bismuth and thallium. Acknowledgments.-The authors wish to thank Dr. K. W. Bagnall, Professor Charles D. Coryell, Dr. Ralph A. Horne for helpful discussions and for making available polonium and tellurium data prior to publication, and Dr. Ugo Camerini for his continued interest and support.
THE PHOTOTROPY OF MALACHITE GREEN LEUCOCYANIDE IN ETHYL ALCOHOL, CYCLOHEXANE, ETHYLENE DICHLORIDE AND ETHYLIDENE DICHLORIDE, AND SOME MIXTURES OF THEM BY EDWARD 0. HOLMES, JR. Contribution f r o m the Chemical Laboratory of Boston University, Boston, Mass. Received September 24, 1968
The phototropy of malachite green leucocyanide dissolved in alcohol is shown to yield three reverse (dark) reaction products, the original leucocyanide, the carbinol, and (or) the ethyl ether depending on conditions. A mechanism is offered that can explain the formation of these products. The phototropy of this solute dissolved in cyclohexane, ethylene dichloride or ethylidene dichloride and some mixtures of these solvents shows that (1) in pure cyclohexane no carbonium ion (MG)+is formed but that polymerization occurs, (2) that more (MG)f ion is formed on irradiation when ethylene dichloride is used as the solvent than when ethylidene dichloride is used, ( 3 ) that in a solvent composed of mixtures of the above with cyclohexane, that as the proportion of the halogenated hydrocarbon is increased more (MG)+ is formed, and (4)that this begins suddenly when the dielectric constant of the solvent is about 4.5 and rises rapidly. Mechanisms are proposed by which the above and other results may be interpreted.
Part A. Solutions of Malachite Green Leucocyanide (I) in Ethyl Alcohol The phototropy of malachite green leucocyanide (I) has been investigated in dry alcohol and also in mixtures of alcohol and water by a number of authors.'-' The results show that, on irradiation, malachite green leucocyanide (I) dissolved in alcohol is photo-ionized t o yield the carbonium ion (MG) + and the cyanide ion, and that the quantum efficiency of the process is very close to unity. When the source of light is removed, the color of the solution fades with greater or less velocity depending on conditions to a product(s) of unknown composition. This product will yield the brilliantly colored carbonium ion (MG) + on the addition of an acid such as hydrochloric, whereas the original leucocyanide (I) will not. Several mechanisms have been proposed but none is completely satisfactory. In order to elucidate more completely the true mechanism involved in the above changes, the au(1) J. Lifschitz, Ber., 62, 1919 (1919). (2) J. Lifschitz and C. L. Joffe, {bid., 97, 426 (1921). (3) Edith Weyde and W. Frankenburger, Trans. Faraday SOC.,27, 561 (1931). (4) Edith Weyde, W. Frankenburger and W. Zimmerman, 2. physik. Chem., B17, 276 (1932). (5) L. Harris and J. Kaminsky, J . A m . Chem. Soc., 67, 1151, 1154 (1935). (6) F. E.E. Germann and C. L. Gibson, ibid., 6 2 , 110 (1940). (7) J. G.Calvert and H. E. Rechen, ibid., 74,2101 (1952).
thor examined the absorption spectra of the products of the dark reaction formed under various conditions and compared them with those of the leucocyanide (I), the carbinol (11) and the ethyl ether (111). The results, tabulated in Table I, indicate that the composition of the dark reaction (thermal) product is a mixture of the carbinol (11) and the ethyl ether (111), or the leucocyanide (I) itself depending on conditions. TABLE I Amax of pure malachite green,
A.
Amax dark reactionoproducts, A.
1. Leucocyanide (I),2720 HCN(g) added," 2725 2. Carbinol (11),2650 Dry ethyl alc., 2640-2660 3. Ethyl ether (111),2670 OH-, CN-or HaO,2650-2660 Product will not form (MG)' on addition of acid.
If a very small amount of KOH or KCN or water was added to the alcoholic solution of the leucocyanide (I), before irradiation, the dark reaction product was a mixture of the carbinol (11) and the ether (111) with the carbinol (11) present in larger amount, whereas when dry alcohol alone was used as the solvent, the proportion of the ether (111) was larger. On the other hand, when any of the above solutions were saturated with HCN gas, either before or after irradiation, the leucocyanide (I) was
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