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The reduction of samarium(III) trifluoroacetate with potassium in liquid ammonia
J. lnorg. Nucl. Chem., 1959, Vol. 9, pp. 166 to 170. Pergamon Press Ltd. Printed in Northern Ireland
THE REDUCTION OF SAMARIUM(III) TRIFLUOROACETATE WITH POTASSIUM IN LIQUID AMMONIA* GEORGE W. WATT and M. L. MUGA~" Department of Chemistry, The University of Texas, Austin 12, Texas (Received 3 February 1958; in revised form 25 June 1958)
Abstract--The reduction of samarium(III) trifluoroacetate with potassium in liquid ammonia provides evidence for only the transitory existence of Sm~+. The nature of the products resulting from the reduction of this salt with one, two, and three equivalents of potassium is described. Procedures are given for the preparation of the trifluoroacetate.and the corresponding 2-ammoniate. IN earlier papers from tb_is laboratory we have described the detection of species involving unusual oxidation states of transitional metals (1-4) by means of potentiometric titrations employing liquid ammonia solutions of potassium/5,6~ The present paper is concerned with efforts to detenrtine whether this and/or related techniques might be applicable to the detection of lower oxidation states of the lanthanides. For this evaluation, samarium was selected because of its well known 2 + oxidation state and the possibility (7) of the 1+ state. The selection of a suitable samarium(Ill) salt for use in this work was a major problem. Earlier work has shown that most simple salts of the lanthanides are either insoluble in liquid ammonia or ammonolyse either partially or completely; a noteworthy exception is the normal acetate which is slightly soluble but stable toward ammonolysis. (8) Despite the obvious complications introduced through the use of a salt involving a potentially reducible anion, samarium(Ill) trifluoroacetate was used because it is both soluble in ammonia and not ammonolysed at or below --33.5 °" Although these studies failed to result in the detection of any stable lower oxidation states of samarium, it seems worthwhile to record at least briefly the results of certain of the experiments. The experiments described below show that samarium(Ill) trifluoroacetate reacts with successive one, two, and three molar equivalent quantities of potassium in ammonia. Although unstable brown products that are strongly indicative of the Sm ~+ ion were observed, all of the samarium-containing products isolated contained samarium in the 3 + oxidation state; neither was there evidence for the formation o f elemental samarium by either direct reduction or disproportionation. Potassium trifluoroacetate was identified as a reaction product; this suggests the formation of * This work was supported in part by the Atomic Energy Commission, Contract AT-(40-1)-1639. I" Present address: Radiation Laboratory, The University of California, Berkeley, California. tl) G. (a) G. (a) G. (4) G. ts~ G. tal G. (7) H. la) G.
W. WATT, M. T. WALLING, JR. and P. I. MAYFIELD,J. A m e r . Chem. Soc. 75, 6175 (1953). W. WATT and P. I. MAYFIELD,J. A m e r . Chem. Soc. 75, 6178 (1953). W. WATT, J. L. HALL, G. R. CHOPPIN and P. S. GENTILE, J. A m e r . Chem. Soc. 76, 373 (1954). W. WATT, R. E. MCCARLEY and J. W. DAWES, J. A m e r . Chem. Soc. 79, 5163 (1957). W. WATT and J. B. OTTO, JR., J. Electrochem. Soc. 98, 1 (1951). W. WATT and D. M. SOWARDS, J. Electrochem. Soc. 102, 46, 545 (1955). A. EICK, N. C. BAENZIGER and L. EYRING, J. A m e r . Chem. Soc. 78, 5147 (1956). W. WATI and P. S. GENTILE, Unpublished work. 166
The reduction of samarium(Ill) trifluoroacetate with potassium in liquid ammonia
167
ammonobasic trifluoroacetates of samarium, but the nitrogen content of the products was incompatible with any such interpretation. While the white ammonia-insoluble products isolated were of reproducible composition, they apparently consisted of mixtures; efforts to separate these products were unsuccessful. In independent experiments, it was established that the consumption of potassium in these reactions was not attributable to catalysed reactions with the solvent, or to the cleavage of C - - F bonds. As shown below, however, reduction of the acetate ion may be involved. Thus, while ammonium trifluoroacetate reacts with potassium only to the extent of reduction of the ammonium ion, the reaction of trifluoroacetic anhydride with liquid ammonia, (FsCCO)20 4- 2NHs--* NH4+ + F3CCO2- 4- FsCCONH2 followed by reduction with potassium consumes a total of three equivalents of potassium. Since one equivalent is consumed in the reduction of the ammonium ion and since formation of the dipotassium salt of the amide seems highly improbable, reduction of the carbonyl group is indicated. This interpretation is supported by the report by GILMAN and JONES (9) that trifluoroacetamide is reduced to the alcohol whereas the corresponding ethyl and n-butyl esters are stable toward reduction under the same conditions. It is noteworthy however that these experiments do not preclude the possibility of C - - C bond cleavage, even though trifluoroacetic acid is stable toward strong reducing agents such as lithium aluminium hydride31°) EXPERIMENTAL Materials
With the exceptions noted below, all materials used were anhydrous reagent grade chemicals. Samarium(III) trifluoroacetate was prepared (in substantially quantitative yield), in a typical ease, by the reaction between 1.61 g of samarium(III) oxide, 10 ml of trifluoroacetic acid, and 2.5 ml (25 per cent excess) of trifluoroacetic anhydride in a sealed Pyrex tube. Since the initial reaction is strongly exothermal, the tube and contents was held at room temperature for 6 hr, then heated for 24 hr at 100°. The supernatant liquid was decanted and the white residual solid was dried in vaeuo for 8 h r at 100°. (Found: Sin, 30.4. Calc. for Sm(C~FsO~)s: Sin, 30.7~). That this salt is not solvolysed by liquid ammonia was demonstrated as follows; at the same time further purification was achieved and the trifluoroacetate was converted to a form suitable for use as a starting material in subsequent studies. The white solid was dissolved in anhydrous liquid ammonia at --33.5 °, filtered to remove a very small quantity of white insoluble solid (presumably unreacted oxide), and the solvent was evaporated to provide the white crystalline 2-ammoniate which was dried in vacuo at room temperature for 2 hr. (Found: Sm, 28.1; N, 4.89; C, 13.6; H, 1-23. Calc. for Sm(C~FsO2)s.2NHs: Sin, 28-7; N, 5.35; C, 13.8; H, 1.16~). Potassium trifluoroacetate was prepared by neutralizing trifluoroacetic acid with potassium hydroxide followed by crystallization and drying in vacuo at 100°, and potassium 1:1 :l-trifluoroethoxide (which was once considered as a possible product of the hydrolysis of reduction reaction products) was prepared in quantitative yield Cgl H . GILMAN a n d R. G . JONES, d. Amer. Chem. Soc. 70, 1281 (1948). (in) A. L. HENNE, R. M. ALM a n d M. SMOOK, J. Amer. Chem. Soc. 70, 1968 (1948).
168
GEORGE W. WATT and M. L. MUGA
from the reaction between potassium and the corresponding alcohol; the latter was prepared as described by HENNE et al. ~1°~ X-ray diffraction data for the four materials described above are given in Table 1. TABLE 1.--X-RAY DIFFRACTION DATA Sm(C2FaO2)3
Sm(CzFaOz)a'2NHa
d (A)
1/Io
d (4)
/]Io
9.48 8.12 4.55 4"07 2'60 2'06
0"9 1'0 0.9 0.9 0.8 0.5 ~'
7"58 6"19 5"15 4"48 4"01
0"7 0"7 I'0 0"5 ~ 0"7
KOCHzCF 3
K(C~FsO~)
d (,~1
1/lo
d (4)
2"93 2"85 2"78 2"51 2"48 2"34 1 "86
1.0 0.9 0.7 0"3 0.3 0.3 0.3 a
5"02 3.84 3.47 3.19 2.64 2.58 2.52
I/lo
I !
0-5 1.0 0.8 0.4 0.4 0.4" 0-5
a Less intense lines not included here.
Methods
Potentiometric titrations in liquid ammonia were carried out using equipment and procedures described elsewhere/5,6l The potassium used in these titrations was redistilled and stored in tared glass ampoules/11~ Reactions in liquid ammonia on a larger scale were carried out using equipment and procedures similar to those described by WATT and KEENANJ12) All reactions in ammonia at both --33-5 and --70 ° were effected under strictly anhydrous conditions; transfers of both starting materials and reaction products were made in an anhydrous oxygen-free atmosphere. X-ray diffraction patterns were obtained with a Hayes spectrograph using CuK~ 1 radiation, a tube voltage of 30 kV, a filament current of 15 mA, and exposure times of 4-6 hr. Magnetic susceptibility measurements were made with a modified CurieCheneveau balance. ~13) Infra-red spectra were obtained using a Baird Model 4-55 (11) G. W. WATT and D. M. SOWARDS,J. Amer. Chem. Soc. 76, 4742 (1955). t12~ G. W. WATT and C. W. KEENAN,J. Amer. Chem. Soc. 71, 3833 {1949). Ila) F . W . GRAY and J. FARQUHARSON, J. Sci. lnstrum. 9, 1 (1932).
The reduction of samarium(Ill) trifluoroacetate with potassium in liquid ammonia
169
infra-red spectrometer; pellet samples (1 per cent in spectroscopically pure KBr) were prepared in an inert atmosphere.
Potentiometric titrations In a typical experiment, 0.328 g (0"670 mmole) of samarium(Ill) trifluoroacetate and 0.111 g (2.85 mmoles) of potassium were dissolved in 24-7 and 31-0 ml of liquid ammonia, respectively; 18.8 ml of the trifluoroacetate solution was transferred to the titration cell and titrated with the potassium solution at --34 °. During the early stages of the titration, the gradual increase in potential was most evident in the regions corresponding to one and two equivalents of added titrant, but these "end-points" were not convincing. For example, the increase in potential near the second equivalence point amounted to only 130 inV. When potassium in excess of two equivalents was added, a white gelatinous precipitate began to form and a major increase in potential occurred after three equivalents of potassium were added; at this point the rate of utilization of the added potassium decreased markedly. Essentially the same observations were made when tke titrations were carried out at -70 °, but the changes in potential corresponding to both one and two equivalents of potassium were more pronounced.
Reduction Of the trifluoroacetate ion This possibility was studied by the potentiometric titration of ammonium trifluoroacetate with potassium and the titration of an equimolar mixture of ammonium trifluoroacetate and trifluoroacetamide with potassium. Thus, 0.358 g of trifluoroacetic acid was dissolved in 33"1 ml of liquid ammonia to provide a 0"0948 molar solution of ammonium trifluoroacetate; this was titrated at 34 ° with 0-328 molar potassium solution. The potassium solution reacted instantaneously, hydrogen was evolved, and a sharp increase in potential anaounting to 0"6 V occurred after addition of eactly one equivalent of the titrant. Similarly, 0.458 g of trifluoroacetic anhydride was treated with 30 ml of liquid ammonia and th,z resulting solution was titrated at --34 ° with 0-418 molar potassium solution. The first significant change in potential was observed after addition of one equivalent of the potassium solution; during the addition of this quantil:y of titrant, hydrogen evolution was observed. Thereafter, hydrogen was not evolved, and after the addition of two more equivalents of the titrant another major change in potential was observed and the solution remained blue fi)r several hours. Reduction of samarium(II1) triJtuoroacetate with potassium (1:1) In a typical experiment, 4-406 g (8'42 mmoles) of samarium(Ill) trifluoroacctate 2-ammoniate was dissolved in 25 1331of liquid ammonia and treated with a solution of 0-329 g (9"42 mmoles) of potassium over a period of 5 rain. At the point of contact of the two solutions, a rust-brown solution and/or precipitate formed but was at once converted to a white precipitate which then dissolved to give a colourless solution. The solvent was evaporated and the solid residue was dried in L,acuo at room temperature and without contact ~ith the atmosphere. (Found: Sin, 27.4; N, 2.77°~i: N/SIn, 1"09; /~, 1"55 B.M.) Data from an X-ray diffraction pattern led to an unequivocal identification of potassium trifluoroacetate ( d - - 5.08, 3-81, 3-47, and 2.55 A). Comparison of the infra-red spectrum of this product with the spectra
170
GEORGE W. WATT a n d M. L. MUGA
of samarium(III) trifluoroacetate 2-ammoniate and potassium trifluoroacetate led to the identification of both of these substances as components of the reaction product. The former exhibits a characteristic peak ~la) at 7.28/~; the latter is characterized by peaks at 12.43 and 7.99/t.
Reduction of samarium(III) trifluoroacetate with potassium (1:2) Samarium(III) trifluoroacetate 2-ammoniate (1.60g; 3.06 mmoles) in 50ml of ammonia was reduced with a solution containing 0.228 g (5.83 mmoles) of potassium. The observations were the same as described above; evaporation of the solvent followed by drying yi,~lded a grey-white solid. (Found: Sm, 25"8~o; #, 2.13 B.M.). Again, potassium trituoroacetate was identified by means of its X-ray diffraction pattern and infra-red spectrum; the latter hov~ever did not show evidence of the presence of Sm(C2FsO2)s'2NH 3.
Reduction of samarium(III) trifluoroacetate with potassium (1:3) In a typical experiment, 2.546 g (4.87 mmoles) of samarium(Ill) trifluoroacetate 2-ammoniate dissolved in 25 ml of ammonia was treated with a solution containing 0.584 g (14.95 mmoles) of potassium (i.e., K/Sm = 3.07). After digestion at --33.5 ° for 1 hr, the white flocculent precipitate was separated from the colourless supernatant solution by filtration and the solid product was washed six times with 20 rnl portions of ammonia. Evaporation of the solvent from the combined supernatant solution and washings provided a white solid. (Found: K, 26.2; Sin, 0"25; N, 0-43. Calcd. for KC2FzOz: K, 25.7 ~). This product gave an X-ray diffraction pattern substantially identical with that given in Table 1 for potassium trifluoroacetate. The grey-white ammonia-insoluble product was dried in vacuo at room temperature. (Found: Sm, 45.3; K, 17.5; N, 1.06; C, 5.39; H, 0.75~; #, 1.95B.M.). This material failed to give an X-ray diffraction pattern and the infra-red spectrum could not be correlated with that of any known compounds of samarium. If it is assumed that the small nitrogen content of this material is attributable to residual solvent and that the analytical values for hydrogen are correspondingly high, the analytical data are in accord with the empirical formula, Sm2KzOsCzHF6. Efforts to demonstrate that this product might be a mixture involved treatment with different solvents under a variety of conditions; however, separations could not be effeeted. Similarly, efforts to establish the identity of these products through the study of their hydrolysis reactions led to results that were reproducible but inconclusive. ~a4~ For further details see: M . L . MUGA, Dissertation, The University of Texas (1957).
THE REDUCTION OF SAMARIUM(III) TRIFLUOROACETATE WITH POTASSIUM IN LIQUID AMMONIA* GEORGE W. WATT and M. L. MUGA~" Department of Chemistry, The University of Texas, Austin 12, Texas (Received 3 February 1958; in revised form 25 June 1958)
Abstract--The reduction of samarium(III) trifluoroacetate with potassium in liquid ammonia provides evidence for only the transitory existence of Sm~+. The nature of the products resulting from the reduction of this salt with one, two, and three equivalents of potassium is described. Procedures are given for the preparation of the trifluoroacetate.and the corresponding 2-ammoniate. IN earlier papers from tb_is laboratory we have described the detection of species involving unusual oxidation states of transitional metals (1-4) by means of potentiometric titrations employing liquid ammonia solutions of potassium/5,6~ The present paper is concerned with efforts to detenrtine whether this and/or related techniques might be applicable to the detection of lower oxidation states of the lanthanides. For this evaluation, samarium was selected because of its well known 2 + oxidation state and the possibility (7) of the 1+ state. The selection of a suitable samarium(Ill) salt for use in this work was a major problem. Earlier work has shown that most simple salts of the lanthanides are either insoluble in liquid ammonia or ammonolyse either partially or completely; a noteworthy exception is the normal acetate which is slightly soluble but stable toward ammonolysis. (8) Despite the obvious complications introduced through the use of a salt involving a potentially reducible anion, samarium(Ill) trifluoroacetate was used because it is both soluble in ammonia and not ammonolysed at or below --33.5 °" Although these studies failed to result in the detection of any stable lower oxidation states of samarium, it seems worthwhile to record at least briefly the results of certain of the experiments. The experiments described below show that samarium(Ill) trifluoroacetate reacts with successive one, two, and three molar equivalent quantities of potassium in ammonia. Although unstable brown products that are strongly indicative of the Sm ~+ ion were observed, all of the samarium-containing products isolated contained samarium in the 3 + oxidation state; neither was there evidence for the formation o f elemental samarium by either direct reduction or disproportionation. Potassium trifluoroacetate was identified as a reaction product; this suggests the formation of * This work was supported in part by the Atomic Energy Commission, Contract AT-(40-1)-1639. I" Present address: Radiation Laboratory, The University of California, Berkeley, California. tl) G. (a) G. (a) G. (4) G. ts~ G. tal G. (7) H. la) G.
W. WATT, M. T. WALLING, JR. and P. I. MAYFIELD,J. A m e r . Chem. Soc. 75, 6175 (1953). W. WATT and P. I. MAYFIELD,J. A m e r . Chem. Soc. 75, 6178 (1953). W. WATT, J. L. HALL, G. R. CHOPPIN and P. S. GENTILE, J. A m e r . Chem. Soc. 76, 373 (1954). W. WATT, R. E. MCCARLEY and J. W. DAWES, J. A m e r . Chem. Soc. 79, 5163 (1957). W. WATT and J. B. OTTO, JR., J. Electrochem. Soc. 98, 1 (1951). W. WATT and D. M. SOWARDS, J. Electrochem. Soc. 102, 46, 545 (1955). A. EICK, N. C. BAENZIGER and L. EYRING, J. A m e r . Chem. Soc. 78, 5147 (1956). W. WATI and P. S. GENTILE, Unpublished work. 166
The reduction of samarium(Ill) trifluoroacetate with potassium in liquid ammonia
167
ammonobasic trifluoroacetates of samarium, but the nitrogen content of the products was incompatible with any such interpretation. While the white ammonia-insoluble products isolated were of reproducible composition, they apparently consisted of mixtures; efforts to separate these products were unsuccessful. In independent experiments, it was established that the consumption of potassium in these reactions was not attributable to catalysed reactions with the solvent, or to the cleavage of C - - F bonds. As shown below, however, reduction of the acetate ion may be involved. Thus, while ammonium trifluoroacetate reacts with potassium only to the extent of reduction of the ammonium ion, the reaction of trifluoroacetic anhydride with liquid ammonia, (FsCCO)20 4- 2NHs--* NH4+ + F3CCO2- 4- FsCCONH2 followed by reduction with potassium consumes a total of three equivalents of potassium. Since one equivalent is consumed in the reduction of the ammonium ion and since formation of the dipotassium salt of the amide seems highly improbable, reduction of the carbonyl group is indicated. This interpretation is supported by the report by GILMAN and JONES (9) that trifluoroacetamide is reduced to the alcohol whereas the corresponding ethyl and n-butyl esters are stable toward reduction under the same conditions. It is noteworthy however that these experiments do not preclude the possibility of C - - C bond cleavage, even though trifluoroacetic acid is stable toward strong reducing agents such as lithium aluminium hydride31°) EXPERIMENTAL Materials
With the exceptions noted below, all materials used were anhydrous reagent grade chemicals. Samarium(III) trifluoroacetate was prepared (in substantially quantitative yield), in a typical ease, by the reaction between 1.61 g of samarium(III) oxide, 10 ml of trifluoroacetic acid, and 2.5 ml (25 per cent excess) of trifluoroacetic anhydride in a sealed Pyrex tube. Since the initial reaction is strongly exothermal, the tube and contents was held at room temperature for 6 hr, then heated for 24 hr at 100°. The supernatant liquid was decanted and the white residual solid was dried in vaeuo for 8 h r at 100°. (Found: Sin, 30.4. Calc. for Sm(C~FsO~)s: Sin, 30.7~). That this salt is not solvolysed by liquid ammonia was demonstrated as follows; at the same time further purification was achieved and the trifluoroacetate was converted to a form suitable for use as a starting material in subsequent studies. The white solid was dissolved in anhydrous liquid ammonia at --33.5 °, filtered to remove a very small quantity of white insoluble solid (presumably unreacted oxide), and the solvent was evaporated to provide the white crystalline 2-ammoniate which was dried in vacuo at room temperature for 2 hr. (Found: Sm, 28.1; N, 4.89; C, 13.6; H, 1-23. Calc. for Sm(C~FsO2)s.2NHs: Sin, 28-7; N, 5.35; C, 13.8; H, 1.16~). Potassium trifluoroacetate was prepared by neutralizing trifluoroacetic acid with potassium hydroxide followed by crystallization and drying in vacuo at 100°, and potassium 1:1 :l-trifluoroethoxide (which was once considered as a possible product of the hydrolysis of reduction reaction products) was prepared in quantitative yield Cgl H . GILMAN a n d R. G . JONES, d. Amer. Chem. Soc. 70, 1281 (1948). (in) A. L. HENNE, R. M. ALM a n d M. SMOOK, J. Amer. Chem. Soc. 70, 1968 (1948).
168
GEORGE W. WATT and M. L. MUGA
from the reaction between potassium and the corresponding alcohol; the latter was prepared as described by HENNE et al. ~1°~ X-ray diffraction data for the four materials described above are given in Table 1. TABLE 1.--X-RAY DIFFRACTION DATA Sm(C2FaO2)3
Sm(CzFaOz)a'2NHa
d (A)
1/Io
d (4)
/]Io
9.48 8.12 4.55 4"07 2'60 2'06
0"9 1'0 0.9 0.9 0.8 0.5 ~'
7"58 6"19 5"15 4"48 4"01
0"7 0"7 I'0 0"5 ~ 0"7
KOCHzCF 3
K(C~FsO~)
d (,~1
1/lo
d (4)
2"93 2"85 2"78 2"51 2"48 2"34 1 "86
1.0 0.9 0.7 0"3 0.3 0.3 0.3 a
5"02 3.84 3.47 3.19 2.64 2.58 2.52
I/lo
I !
0-5 1.0 0.8 0.4 0.4 0.4" 0-5
a Less intense lines not included here.
Methods
Potentiometric titrations in liquid ammonia were carried out using equipment and procedures described elsewhere/5,6l The potassium used in these titrations was redistilled and stored in tared glass ampoules/11~ Reactions in liquid ammonia on a larger scale were carried out using equipment and procedures similar to those described by WATT and KEENANJ12) All reactions in ammonia at both --33-5 and --70 ° were effected under strictly anhydrous conditions; transfers of both starting materials and reaction products were made in an anhydrous oxygen-free atmosphere. X-ray diffraction patterns were obtained with a Hayes spectrograph using CuK~ 1 radiation, a tube voltage of 30 kV, a filament current of 15 mA, and exposure times of 4-6 hr. Magnetic susceptibility measurements were made with a modified CurieCheneveau balance. ~13) Infra-red spectra were obtained using a Baird Model 4-55 (11) G. W. WATT and D. M. SOWARDS,J. Amer. Chem. Soc. 76, 4742 (1955). t12~ G. W. WATT and C. W. KEENAN,J. Amer. Chem. Soc. 71, 3833 {1949). Ila) F . W . GRAY and J. FARQUHARSON, J. Sci. lnstrum. 9, 1 (1932).
The reduction of samarium(Ill) trifluoroacetate with potassium in liquid ammonia
169
infra-red spectrometer; pellet samples (1 per cent in spectroscopically pure KBr) were prepared in an inert atmosphere.
Potentiometric titrations In a typical experiment, 0.328 g (0"670 mmole) of samarium(Ill) trifluoroacetate and 0.111 g (2.85 mmoles) of potassium were dissolved in 24-7 and 31-0 ml of liquid ammonia, respectively; 18.8 ml of the trifluoroacetate solution was transferred to the titration cell and titrated with the potassium solution at --34 °. During the early stages of the titration, the gradual increase in potential was most evident in the regions corresponding to one and two equivalents of added titrant, but these "end-points" were not convincing. For example, the increase in potential near the second equivalence point amounted to only 130 inV. When potassium in excess of two equivalents was added, a white gelatinous precipitate began to form and a major increase in potential occurred after three equivalents of potassium were added; at this point the rate of utilization of the added potassium decreased markedly. Essentially the same observations were made when tke titrations were carried out at -70 °, but the changes in potential corresponding to both one and two equivalents of potassium were more pronounced.
Reduction Of the trifluoroacetate ion This possibility was studied by the potentiometric titration of ammonium trifluoroacetate with potassium and the titration of an equimolar mixture of ammonium trifluoroacetate and trifluoroacetamide with potassium. Thus, 0.358 g of trifluoroacetic acid was dissolved in 33"1 ml of liquid ammonia to provide a 0"0948 molar solution of ammonium trifluoroacetate; this was titrated at 34 ° with 0-328 molar potassium solution. The potassium solution reacted instantaneously, hydrogen was evolved, and a sharp increase in potential anaounting to 0"6 V occurred after addition of eactly one equivalent of the titrant. Similarly, 0.458 g of trifluoroacetic anhydride was treated with 30 ml of liquid ammonia and th,z resulting solution was titrated at --34 ° with 0-418 molar potassium solution. The first significant change in potential was observed after addition of one equivalent of the potassium solution; during the addition of this quantil:y of titrant, hydrogen evolution was observed. Thereafter, hydrogen was not evolved, and after the addition of two more equivalents of the titrant another major change in potential was observed and the solution remained blue fi)r several hours. Reduction of samarium(II1) triJtuoroacetate with potassium (1:1) In a typical experiment, 4-406 g (8'42 mmoles) of samarium(Ill) trifluoroacctate 2-ammoniate was dissolved in 25 1331of liquid ammonia and treated with a solution of 0-329 g (9"42 mmoles) of potassium over a period of 5 rain. At the point of contact of the two solutions, a rust-brown solution and/or precipitate formed but was at once converted to a white precipitate which then dissolved to give a colourless solution. The solvent was evaporated and the solid residue was dried in L,acuo at room temperature and without contact ~ith the atmosphere. (Found: Sin, 27.4; N, 2.77°~i: N/SIn, 1"09; /~, 1"55 B.M.) Data from an X-ray diffraction pattern led to an unequivocal identification of potassium trifluoroacetate ( d - - 5.08, 3-81, 3-47, and 2.55 A). Comparison of the infra-red spectrum of this product with the spectra
170
GEORGE W. WATT a n d M. L. MUGA
of samarium(III) trifluoroacetate 2-ammoniate and potassium trifluoroacetate led to the identification of both of these substances as components of the reaction product. The former exhibits a characteristic peak ~la) at 7.28/~; the latter is characterized by peaks at 12.43 and 7.99/t.
Reduction of samarium(III) trifluoroacetate with potassium (1:2) Samarium(III) trifluoroacetate 2-ammoniate (1.60g; 3.06 mmoles) in 50ml of ammonia was reduced with a solution containing 0.228 g (5.83 mmoles) of potassium. The observations were the same as described above; evaporation of the solvent followed by drying yi,~lded a grey-white solid. (Found: Sm, 25"8~o; #, 2.13 B.M.). Again, potassium trituoroacetate was identified by means of its X-ray diffraction pattern and infra-red spectrum; the latter hov~ever did not show evidence of the presence of Sm(C2FsO2)s'2NH 3.
Reduction of samarium(III) trifluoroacetate with potassium (1:3) In a typical experiment, 2.546 g (4.87 mmoles) of samarium(Ill) trifluoroacetate 2-ammoniate dissolved in 25 ml of ammonia was treated with a solution containing 0.584 g (14.95 mmoles) of potassium (i.e., K/Sm = 3.07). After digestion at --33.5 ° for 1 hr, the white flocculent precipitate was separated from the colourless supernatant solution by filtration and the solid product was washed six times with 20 rnl portions of ammonia. Evaporation of the solvent from the combined supernatant solution and washings provided a white solid. (Found: K, 26.2; Sin, 0"25; N, 0-43. Calcd. for KC2FzOz: K, 25.7 ~). This product gave an X-ray diffraction pattern substantially identical with that given in Table 1 for potassium trifluoroacetate. The grey-white ammonia-insoluble product was dried in vacuo at room temperature. (Found: Sm, 45.3; K, 17.5; N, 1.06; C, 5.39; H, 0.75~; #, 1.95B.M.). This material failed to give an X-ray diffraction pattern and the infra-red spectrum could not be correlated with that of any known compounds of samarium. If it is assumed that the small nitrogen content of this material is attributable to residual solvent and that the analytical values for hydrogen are correspondingly high, the analytical data are in accord with the empirical formula, Sm2KzOsCzHF6. Efforts to demonstrate that this product might be a mixture involved treatment with different solvents under a variety of conditions; however, separations could not be effeeted. Similarly, efforts to establish the identity of these products through the study of their hydrolysis reactions led to results that were reproducible but inconclusive. ~a4~ For further details see: M . L . MUGA, Dissertation, The University of Texas (1957).