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Uranyl bromides obtained from aqueous solution
J. Inorg. Nucl. Chem., 1961, Vol. 17, pp. 135 to 137. Pergamon Press Ltd.
URANYL BROMIDES OBTAINED FROM AQUEOUS SOLUTION SIGFRED PETERSON Oak Ridge National Laboratory, Oak Ridge, Tennessee (Received 28 March 1960; in revised form 12 August 1960)
Abstraet--Uranyl bromide can be crystallized from acid solution as the very hygroscopic trihydrate. Part of the water can be removed at 60°C without decomposition, but irreversible decomposition takes place at 115°C. Its saturated solution is 6"5 M, viscous, very dark red and of density 3"36 g/ml. RecrystaUization from ether or isopropanol yields organic solvate-hydrates. The basic bromide, UOz(OH)Br-2HzO, has been crystallized from acid-deficient uranyl bromide solutions. It forms stable dilute aqueous solutions, but its concentrated solutions deposit hydrated uranium trioxide. NEARLY all the w o r k o n u r a n y l b r o m i d e s p r e p a r e d f r o m s o l u t i o n is quite old a n d has been s u m m a r i z e d b y KATZ a n d RAmNOWIXCH ¢1~. A n h y d r o u s u r a n y l b r o m i d e can be o b t a i n e d
Solutions of uranyl bromide are readily prepared by dissolving uranium trioxide in hydrobromic acid. These solutions must be concentrated by evaporation before crystallization can take place. An unmeasured excess of acid was used to decrease the solubility of the bromide and to compensate for loss of acidity during evaporation, which could lead to formation of the basic bromide. After the solution was concentrated to a tliick, deep-red, nearly opaque syrup, crystals formed on cooling. However, if evaporation was carried out until the solution approached the composition of the solid, the solid bromide formed a cement-like cake hard to remove from the vessel without redissolution. After crystallization, the uranyl bromide was separated from the bulk of the liquid on a coarse sintered glass filter connected to the building vacuum system. The remaining water and excess Ill j. j. KATZ and E. RABINOWlTCH,The Chemistry of Uranium, (Edited by E. Rabinovitch) I'qNES Plutonium Project Record Division VIII, 5, pp. 590-593. McGraw-Hill (1951). t2) j. PRIGENr, C.R. Acad. Sci., Paris 247, 1737 (1958). c3J S. A. SHCHUKAREV,I. V. VAmL'KOVA,V. M. PROZDOVAand K. E. FRANTSEVA,Russ. J. lnorg. Chem. (English Translation) 4, 15 (1959). ~'~ C. A. KRAUS,Manhattan District Report A-360 (1942). 135
136
SfGFRED PETERSON
hydrobromic acid were evaporated by stoppering the top of the filter and continuing the vacuum for from several hours to three flays. Washing the solution from the crystals was impossible since uranyl bromide is soluble in water-miscible liquids. The crystals varied in colour from yellow-orange to redorange; traces of occluded intensely coloured solution probably masked the true yellow colour. The yellow colour typical of uranyl salts has been observed on rehydration of bromide samples dried and partly decomposed by heating at 175°C. The bromide could be stored in glass-stoppered vessels in a desiccator; on exposure to air it rapidly deliquesced. It did not evolve hydrogen bromide on standing at room temperature, as claimed x in the early work. The density of the hydrated bromide. determined by benzene displacement, was 4.32 g/ml. (Found: U, 49.3, 49'2, 48.8; Br, 32.9, 33'6. 32.5; H20, 11"51. 10"48. 10'62. Calc. for UO~Br~..3H~O; U, 49'2; Br, 33.0; H~O, 11-2,°,~,).
Solubility of UO2Br2"3H20 A small volume of water was added to uranyl bromide hydrate, and after dissolution successive portions of solid were added until undissolved solid remained on standing overnight. Over a four-day period portions of the solution were withdrawn into a 500 ,,1 pipette, weighed, and analyzed for uranium and for bromide ion. The averages and average deviations found were uranium, 6.51 :: 0.06 M; bromide, 13"0 ~ 0.1 M; density, 3.36 - 0.01 g/ml; no trend with time was observable.
Crystallization of uranyl bromide from or~,aoic soh,ents Uranyl bromide is known m to be soluble in organic oxygen compounds and to form addition compounds with some of them. Attempts to crystallize uranyl bromide, by vacuum evaporation at room temperature of solutions of the hydrate in ethyl ether and in isopropyl alcohol, yielded yelloworange crystals containing both water and organic solvent. Attempted evaporation of the organic solutions by heating resulted in reduction of uranium to a black insoluble powder.
Thermal decon~osition of hydrated uranyl bromide The weight changes of several samples of UO..,Br~.3HzO were observed for different periods of heating. Loss of about one-third of the water was achieved at 60 C without decomposition. Partial decomposition to various yellow solids resulted at 125-175 C. At 200-350 C, the decomposition product was brick red, amorphous to X-rays, and identified as nearly pure uranium trioxide by its ease of solution in hydrochloric acid and the only very slight turbidity resulting from adding silver nitrate to its solution in nitric acid. The weight loss on decomposition corresponded to the formation of UOa'H20 at 200' C and UOa at 35ffC. It is notable that a brick-red form of uranium dioxide has been claimed c~ as a decomposition product of the anhydrous bromide.
Preparation of basic uranyl bromide The basic uranyl bromide was first observed during attempts to crystallize the normal bromide from aqueous solution. Observations made during this investigation indicate that the basic bromide is the saturating solid at room temperature for solutions ranging in bromide/uranium ratio from 1"1 to near 2; this is very similar to the behaviour reported by KRAUSc4~ for the analogous chloride. If equimolar quantities of uranium trioxide and hydrobromic acid are combined, the solid precipitating is the hydrated oxide and not the basic bromide. When uranium trioxide was dissolved in hot uranyl bromide solution and crystallization allowed to take place, the solid phases included the basic bromide. The bromide/uranium ratio was kept well above the room-temperature limit of 1'1 to avoid precipitation of the oxide during cooling. The solids were collected on a sintered-glass filter and washed with isopropanol or ethyl ether to remove normal bromide. The fine yellow needles obtained were stable to the atmosphere, not visibly soluble in ethyl ether, isopropanol, or an ethyl ether solution of uranyl bromide. The density, determined by benzene displacement, was 4.95 g/ml. The X-ray diffraction pattern is given in Table 1. (Found: U, 58"7; Br, 19'8; H20, 13.24; OH-, 2"33 meq/g: Calc. for UO2(OH)Br-2H20: U, 59"1; Br, 19.8; H.~O, 13"4 (the OH- ion responds to the analysis as a water molecule); OH-, 2"48 meq/g).
btteraction of the basic bromide with water Basic uranyl bromide dissolved readily when mixed rapidly with sufficient water to give dilute solutions. These solutions were more intensely coloured than unhydrolyzed uranyl solutions of the same concentration. Solutions as concentrated as 0.1 M lost part of their uranium as precipitated
Uranyl bromides obtained from aqueous solution
137
hydrated oxide on standing several days. Solutions as dilute as 0.01 M appeared stable indefinitely. Concentration by evaporation of a stable basic bromide solution led to oxide deposition. Treatment of basic bromide with insufficient water to consume the sample gave a solution 2.73 M in U(VI), 3.0 M in bromide, and of density 1-87 g/ml. The yellow residue contained two components, unreacted basic bromide which could be dissolved in a large volume of water, and an insoluble material identified by X-ray diffraction as UO3"2H20. Thus the above composition is the solution simultaneously saturated with oxide and basic bromide. The saturating oxide need not be the dihydrate, since hydration may have occurred during the washing to remove from the basic bromide. TABLE I.--X-RAY DIFFRACTIONPATTERNSOF BASICURANYLBROMIDES UO2(OH)Br.2H~O Intensity* IV ~:-- W :->W L'VW 5" /.lOW Ftl :5> W VVW /)W OW ~W m Uvw vl)w vow w
vw ~w ow
d(,~) 8-9 5"4 5-15 4-9 4-4 4.1 3"85 3"65 3"05 3-0 2'94 2"88 2-75 2-69 2.64 2-56 2-52 2.47 2-44 2-37 2.32
UOg(OH)Br
Intensity
d(A)
VVW
2"22 2'12 2"09 2"05 2"01 1 "98 1 "94 1"90 1"865
VVW W W OW OW VW VW VW W W W W VOW W VW W VOW
1"83 1"81 1"77 1 "75 1 "72 1 "66 1"62 1"57 1"53
VW
1'51 1 "48
W
1"35
I)W
Intensity tr/
m W VOW
-:m VOW
S W W W VOW W W ~W W W W W
d(/~,) i Intensity 8-0 7-45 6-4 5.4 4.75 4.45 4.05 3-79 3.70 3.55 3.28 3-18 3"08 2"98 2.90 2"82 2"68 2-58 2.54
i I
w vvw vw
w vw
w w w w vw vvw vvw vw vvw vvw vvw vvw vvw vw
d(A) 2.40 2.34 2.23 2.18 2.10 2.05 1.98 1.94 1.89 1"86 1"76 1"72 1-705 1"68 1"58 1"53 1'51 1 "445 1 "40
* s--strong, m--medium, w--weak, v--very. T h e r m a l d e h y d r a t i o n o f the basic b r o m i d e
The basic bromide, UO2(OH)Br'2H20, was heated overnight at 105°C with no change in appearance or weight. Heating three days at 115°C resulted in a weight loss of 8.10 per cent, and another day at 200°C produced a total loss of 9"15 per cent, corresponding to 2"03 moles of water per mole of basic bromide. The resulting "anhydrous basic bromide" showed a different X-ray diffraction pattern (Table 1) from the hydrated basic bromide and from previously known compounds. Dissolution in water gave a solution similar to that obtained from the hydrated basic bromide. (Found: U, 63-5; Br, 21-3; OH , 2 meq/g. Calc. for UO2(OH)Br: U, 64.9; Br, 21"8; OH-, 2.7 meq/g). CONCLUSIONS Uranyl b r o m i d e has been crystallized f r o m acidic a q u e o u s solutions. It was s h o w n by analysis to be the trihydrate, in agreement with SHCHUKAREV(3) a n d in disagreement with early investigators ~1~ who claimed UO~Brz.7H~O. The previously u n r e p o r t e d basic b r o m i d e has been obtained from acid-deficient u r a n y l b r o m i d e solutions as the dihydrate, U O 2 ( O H ) B r - 2 H 2 0 . This c o m p o u n d can be dehydrated to UO2(OH}Br at 200°C. It is decomposed by water to u r a n i u m trioxide a n d a solution c o n t a i n i n g more b r o m i n e a t o m s t h a n u r a n i u m atoms.
URANYL BROMIDES OBTAINED FROM AQUEOUS SOLUTION SIGFRED PETERSON Oak Ridge National Laboratory, Oak Ridge, Tennessee (Received 28 March 1960; in revised form 12 August 1960)
Abstraet--Uranyl bromide can be crystallized from acid solution as the very hygroscopic trihydrate. Part of the water can be removed at 60°C without decomposition, but irreversible decomposition takes place at 115°C. Its saturated solution is 6"5 M, viscous, very dark red and of density 3"36 g/ml. RecrystaUization from ether or isopropanol yields organic solvate-hydrates. The basic bromide, UOz(OH)Br-2HzO, has been crystallized from acid-deficient uranyl bromide solutions. It forms stable dilute aqueous solutions, but its concentrated solutions deposit hydrated uranium trioxide. NEARLY all the w o r k o n u r a n y l b r o m i d e s p r e p a r e d f r o m s o l u t i o n is quite old a n d has been s u m m a r i z e d b y KATZ a n d RAmNOWIXCH ¢1~. A n h y d r o u s u r a n y l b r o m i d e can be o b t a i n e d
Solutions of uranyl bromide are readily prepared by dissolving uranium trioxide in hydrobromic acid. These solutions must be concentrated by evaporation before crystallization can take place. An unmeasured excess of acid was used to decrease the solubility of the bromide and to compensate for loss of acidity during evaporation, which could lead to formation of the basic bromide. After the solution was concentrated to a tliick, deep-red, nearly opaque syrup, crystals formed on cooling. However, if evaporation was carried out until the solution approached the composition of the solid, the solid bromide formed a cement-like cake hard to remove from the vessel without redissolution. After crystallization, the uranyl bromide was separated from the bulk of the liquid on a coarse sintered glass filter connected to the building vacuum system. The remaining water and excess Ill j. j. KATZ and E. RABINOWlTCH,The Chemistry of Uranium, (Edited by E. Rabinovitch) I'qNES Plutonium Project Record Division VIII, 5, pp. 590-593. McGraw-Hill (1951). t2) j. PRIGENr, C.R. Acad. Sci., Paris 247, 1737 (1958). c3J S. A. SHCHUKAREV,I. V. VAmL'KOVA,V. M. PROZDOVAand K. E. FRANTSEVA,Russ. J. lnorg. Chem. (English Translation) 4, 15 (1959). ~'~ C. A. KRAUS,Manhattan District Report A-360 (1942). 135
136
SfGFRED PETERSON
hydrobromic acid were evaporated by stoppering the top of the filter and continuing the vacuum for from several hours to three flays. Washing the solution from the crystals was impossible since uranyl bromide is soluble in water-miscible liquids. The crystals varied in colour from yellow-orange to redorange; traces of occluded intensely coloured solution probably masked the true yellow colour. The yellow colour typical of uranyl salts has been observed on rehydration of bromide samples dried and partly decomposed by heating at 175°C. The bromide could be stored in glass-stoppered vessels in a desiccator; on exposure to air it rapidly deliquesced. It did not evolve hydrogen bromide on standing at room temperature, as claimed x in the early work. The density of the hydrated bromide. determined by benzene displacement, was 4.32 g/ml. (Found: U, 49.3, 49'2, 48.8; Br, 32.9, 33'6. 32.5; H20, 11"51. 10"48. 10'62. Calc. for UO~Br~..3H~O; U, 49'2; Br, 33.0; H~O, 11-2,°,~,).
Solubility of UO2Br2"3H20 A small volume of water was added to uranyl bromide hydrate, and after dissolution successive portions of solid were added until undissolved solid remained on standing overnight. Over a four-day period portions of the solution were withdrawn into a 500 ,,1 pipette, weighed, and analyzed for uranium and for bromide ion. The averages and average deviations found were uranium, 6.51 :: 0.06 M; bromide, 13"0 ~ 0.1 M; density, 3.36 - 0.01 g/ml; no trend with time was observable.
Crystallization of uranyl bromide from or~,aoic soh,ents Uranyl bromide is known m to be soluble in organic oxygen compounds and to form addition compounds with some of them. Attempts to crystallize uranyl bromide, by vacuum evaporation at room temperature of solutions of the hydrate in ethyl ether and in isopropyl alcohol, yielded yelloworange crystals containing both water and organic solvent. Attempted evaporation of the organic solutions by heating resulted in reduction of uranium to a black insoluble powder.
Thermal decon~osition of hydrated uranyl bromide The weight changes of several samples of UO..,Br~.3HzO were observed for different periods of heating. Loss of about one-third of the water was achieved at 60 C without decomposition. Partial decomposition to various yellow solids resulted at 125-175 C. At 200-350 C, the decomposition product was brick red, amorphous to X-rays, and identified as nearly pure uranium trioxide by its ease of solution in hydrochloric acid and the only very slight turbidity resulting from adding silver nitrate to its solution in nitric acid. The weight loss on decomposition corresponded to the formation of UOa'H20 at 200' C and UOa at 35ffC. It is notable that a brick-red form of uranium dioxide has been claimed c~ as a decomposition product of the anhydrous bromide.
Preparation of basic uranyl bromide The basic uranyl bromide was first observed during attempts to crystallize the normal bromide from aqueous solution. Observations made during this investigation indicate that the basic bromide is the saturating solid at room temperature for solutions ranging in bromide/uranium ratio from 1"1 to near 2; this is very similar to the behaviour reported by KRAUSc4~ for the analogous chloride. If equimolar quantities of uranium trioxide and hydrobromic acid are combined, the solid precipitating is the hydrated oxide and not the basic bromide. When uranium trioxide was dissolved in hot uranyl bromide solution and crystallization allowed to take place, the solid phases included the basic bromide. The bromide/uranium ratio was kept well above the room-temperature limit of 1'1 to avoid precipitation of the oxide during cooling. The solids were collected on a sintered-glass filter and washed with isopropanol or ethyl ether to remove normal bromide. The fine yellow needles obtained were stable to the atmosphere, not visibly soluble in ethyl ether, isopropanol, or an ethyl ether solution of uranyl bromide. The density, determined by benzene displacement, was 4.95 g/ml. The X-ray diffraction pattern is given in Table 1. (Found: U, 58"7; Br, 19'8; H20, 13.24; OH-, 2"33 meq/g: Calc. for UO2(OH)Br-2H20: U, 59"1; Br, 19.8; H.~O, 13"4 (the OH- ion responds to the analysis as a water molecule); OH-, 2"48 meq/g).
btteraction of the basic bromide with water Basic uranyl bromide dissolved readily when mixed rapidly with sufficient water to give dilute solutions. These solutions were more intensely coloured than unhydrolyzed uranyl solutions of the same concentration. Solutions as concentrated as 0.1 M lost part of their uranium as precipitated
Uranyl bromides obtained from aqueous solution
137
hydrated oxide on standing several days. Solutions as dilute as 0.01 M appeared stable indefinitely. Concentration by evaporation of a stable basic bromide solution led to oxide deposition. Treatment of basic bromide with insufficient water to consume the sample gave a solution 2.73 M in U(VI), 3.0 M in bromide, and of density 1-87 g/ml. The yellow residue contained two components, unreacted basic bromide which could be dissolved in a large volume of water, and an insoluble material identified by X-ray diffraction as UO3"2H20. Thus the above composition is the solution simultaneously saturated with oxide and basic bromide. The saturating oxide need not be the dihydrate, since hydration may have occurred during the washing to remove from the basic bromide. TABLE I.--X-RAY DIFFRACTIONPATTERNSOF BASICURANYLBROMIDES UO2(OH)Br.2H~O Intensity* IV ~:-- W :->W L'VW 5" /.lOW Ftl :5> W VVW /)W OW ~W m Uvw vl)w vow w
vw ~w ow
d(,~) 8-9 5"4 5-15 4-9 4-4 4.1 3"85 3"65 3"05 3-0 2'94 2"88 2-75 2-69 2.64 2-56 2-52 2.47 2-44 2-37 2.32
UOg(OH)Br
Intensity
d(A)
VVW
2"22 2'12 2"09 2"05 2"01 1 "98 1 "94 1"90 1"865
VVW W W OW OW VW VW VW W W W W VOW W VW W VOW
1"83 1"81 1"77 1 "75 1 "72 1 "66 1"62 1"57 1"53
VW
1'51 1 "48
W
1"35
I)W
Intensity tr/
m W VOW
-:m VOW
S W W W VOW W W ~W W W W W
d(/~,) i Intensity 8-0 7-45 6-4 5.4 4.75 4.45 4.05 3-79 3.70 3.55 3.28 3-18 3"08 2"98 2.90 2"82 2"68 2-58 2.54
i I
w vvw vw
w vw
w w w w vw vvw vvw vw vvw vvw vvw vvw vvw vw
d(A) 2.40 2.34 2.23 2.18 2.10 2.05 1.98 1.94 1.89 1"86 1"76 1"72 1-705 1"68 1"58 1"53 1'51 1 "445 1 "40
* s--strong, m--medium, w--weak, v--very. T h e r m a l d e h y d r a t i o n o f the basic b r o m i d e
The basic bromide, UO2(OH)Br'2H20, was heated overnight at 105°C with no change in appearance or weight. Heating three days at 115°C resulted in a weight loss of 8.10 per cent, and another day at 200°C produced a total loss of 9"15 per cent, corresponding to 2"03 moles of water per mole of basic bromide. The resulting "anhydrous basic bromide" showed a different X-ray diffraction pattern (Table 1) from the hydrated basic bromide and from previously known compounds. Dissolution in water gave a solution similar to that obtained from the hydrated basic bromide. (Found: U, 63-5; Br, 21-3; OH , 2 meq/g. Calc. for UO2(OH)Br: U, 64.9; Br, 21"8; OH-, 2.7 meq/g). CONCLUSIONS Uranyl b r o m i d e has been crystallized f r o m acidic a q u e o u s solutions. It was s h o w n by analysis to be the trihydrate, in agreement with SHCHUKAREV(3) a n d in disagreement with early investigators ~1~ who claimed UO~Brz.7H~O. The previously u n r e p o r t e d basic b r o m i d e has been obtained from acid-deficient u r a n y l b r o m i d e solutions as the dihydrate, U O 2 ( O H ) B r - 2 H 2 0 . This c o m p o u n d can be dehydrated to UO2(OH}Br at 200°C. It is decomposed by water to u r a n i u m trioxide a n d a solution c o n t a i n i n g more b r o m i n e a t o m s t h a n u r a n i u m atoms.