J. Inorg. Nucl. Chem., 1962, Vol. 24, pp. 387 to 391. Pergamon Press Ltd. Printed in England
PREPARATION OF ANHYDROUS LANTHANIDE HALIDES,
ESPECIALLY IODIDES*
M. D. TAYLOR~and C. P. CARTER
Department of Chemistry, Howard University, Washington D.C.
(Received 29 September 1961 ; in revised form 2 November 1961)
Alutmet--A general method is described which can be used to synthesize nearly all the
lanthanide halidca in high purity and good yield. It involves heating in vacuo, a molecularly
dispersed mixture of hydrated lanthanide halide with the proper ammonium halide until the
water and ammonium halide are expelled to leave pure, anhydrous lanthanide halide.
All tri-halidcs except the iodides of samarium and europium are obtained. These are obtained
a s di-halidcs. Optimum condition for synthesis are discussed. The procedure is the only
one which has been reported for preparing pure anhydrous iodides with relatively simple
apparatus and technique.
MUCH interest exists in the preparation of anhydrous lanthanide halides. These
compounds are used widely for the production of the lanthanide metals both by
electrolytic and metallothermic methods. They are the starting materials from which
many other anhydrous compounds, especially the divalent halides, are prepared.
Anhydrous halides also are required for.thermochemical and physicochemical studies
of the lanthanide compounds, especially in non-aqueous solutions.
Though methods for preparing anhydrous lanthanide compounds have been the
subject of many investigations, these compounds are still difficult to prepare. The
hydrated salts are obtained readily by reaction between the oxides and hydrohalic
acid solutions. Attempts to dehydrate them usually lead to their hydrolysis in
accordance with the equation:
LnCl3q- H20 ~ LnOCI × 2HCI
(I)
or decomposition in accordance with the equation :
Lnlaq-½ 02 ~- LnOl÷i2
(2)
Hydrolysis of chlorides and some bromides can be prevented by performing the
dehydration in an atmosphere of HCI or HBr, but the iodides can not be dehydrated
this way. In such dehydration the hydrogen halide must be completely free of
moisture and oxygen to prevent reactions (l) and (2) from occurring.
The methods which have been reported for preparing anhydrous lanthanide
halides have been presented mainly as individual examples applicable to the preparation of a few special compounds. Except for the preparation of the chlorides, few
methods of general applicability have been published. A review which attempts to
summarize, classify and evaluate the various methods has been submitted for publication.t~)
* Major support for this work was from Research Grant G7334 from the National
Science Foundation.
T Robert A. Welch Visiting Scholar at Prairie View Agricultural and Mechanical
College, Prairie View, Texas, 1960-61.
(1) M. O. TAYLOR,Chem. Revs. To be published.
387
388
M.D. TAYLORand C. P. CARTER
Except for a few miscellaneous ones, the known methods for preparing anhydrous
lanthanide halides generally involve either converting the oxide to the halide with a
suitable halogenating reagent or dehydrating the wet halide.
Up to now no single geheral method has been reported which can be applied
to the preparation of all anhydrous lanthanide halides; the iodides are especially
difficult to prepare. We have succeeded in developing such a method. It consists in
heating, in vacuo, a molecularly dispersed mixture of hydrated lanthanide halide with
the appropriate ammonium halide to expel first the water, then the ammonium halide.
The ammonium halide environment prevents hydrolysis of the lanthanon halide and
a perfectly pure product is obtained. Variations of the procedure have been
reported (2-s) but no systematic studies have been made either to ascertain if the
procedure is suitable for preparing all the lanthanide halides or what the optimum
conditions are for maximum yield and purity. Such conditions have been ascertained
in this study.
q
I"1
~
d
FIG. I.
EXPERIMENTAL
Starting materials. The source of the lanthanide materials was lanthanide oxides,
98-100 per cent pure. They were obtained either from Research Chemicals, Inc., Burbank,
(2) DUBOIN,Annales Scientific d'Ecole Normal Superieure, Paris [3] 5, 416 (1888).
(3) F. EPHRAIMand P. RAY, Ber. Dtsch. Chem. Ges. 62, 1509, 1520, 1639 (1929).
(4) R. HERMANN,J. Prakt. Chem. 82, 385 (1861).
(s~ W. R. HODO~INSON,J. Soc. Chem. Industr. (London), 33, 445 (1914).
(6~ G. JANTSCH,H. JAWREK,N. SKALLAand H. GAWALOWSKV,Z. Anorg. Chem. 207, 353 (1932).
(7~ G. JANTSCH,N. SKALLAand H. JAWUREK,Z. Anorg. Chem. 201, 207 (1931).
(81 M. C. MARIGNAC,Ann. Chim. Phys. [3] 38, 148 (1853).
Preparation of anhydrous lanthanide halides, especially iodides
389
California, or Lindsay Chemical Division, West Chicago, Illinois. Ammonium halides
and hydrochloric acid were reagent grade. Hydrobromic and hydroiodic acids were
prepared by the reaction of tetrahydronaphthalene with bromine or iodine(9) in accordance
with equation:
CioHi2 +22 ~ Cl0Hs +4HI
(3)
General procedure. The general procedure consisted in dissolving the oxide in dilute
hydrohalic acid, adding about 6.0 mole of ammonium halide per mole of lanthanide metal,
and adding next about 50 ml of relatively concentrated hydrohalic acid. The mixture was
evaporated to dryness. Toward the end of the evaporation it must be stirred sufficiently
vigorously to prevent its sticking to the walls of the beaker since it is nearly impossible to
remove stuck material without breaking the beaker. The water and ammonium halide are
removed in the special apparatus shown in Fig. 1. It consists of a Pyrex reaction vessel (A),
with an attached sublimation tube (B), that is attached to a vacuum line manifold (C),
with a ball and socket joint, (H). The vactmm line consisted of a manifold, a manometer (I),
a drying tube (D), a trap (E), and an outlet to the pump (G). The operating details will be
described below for a specific example.
Preparation of YbCI3. Ytterbium oxide, 10.0 g was dissolved with heating in 35.0 ml
of 6 N HCI. Next 154) g NH4CI was added. It failed to dissolve completely. Addition of
50.0 ml of cone. HC1 caused more precipitation but most of the precipitate dissolved on
heating. The mixture was evaporated to dryness and heated to 200°C on the hot plate.
Then it was transferred to the reaction vessel (A), which was sealed. The trap (E) was cooled
by a liquid nitrogen or dry-ice bath and the system was evacuated. The reaction vessel was
surrounded by an electric furnace and heated to 200° C during 1.5 hr. All the water was
driven off and NH4CI began to evolve. Now a cover was placed over the furnace. The
temperature was raised to 430° over a period of 8 hr to sublime all the NH(CI away. The
apparatus was permitted to cool, filled with pure dry N2, and the reaction vessel was removed
to the dry-box. The product weighed 13.2 g for a yield of 82 per cent. It was completely
soluble in water. Some YbCI3 was swept into the sublimation tube by the subliming NH4CI.
It was isolated as the oxalate from which 1.8 g of Yb203 was recovered.
Eighteen lanthanide halides have been prepared. Quantitative data for these are
recorded in Table 1. In addition, qualitative data have been obtained for the preparation
of iodides of H0, Dy, and Tb. The results obtained supports the conclusion that the
ammonium halide method can be used to prepare all anhydrous lanthanide halides.
Analysis. Halide is precipitated with AgNO3. Divalent lanthanide halides must be
oxidized before this precipitation is made. The excess silver was precipitated with hydrohalic
acid. The residual solution is evaporated to proper volume and the lanthanide ion is
precipitated with oxalic acid. The oxalate is ignited and weighed as the lanthanidc oxide.
DISCUSSION
An examinatiori of Table 1 shows that the yields are generally greater than 60
per cent and may exceed 95 per cent. Most material is lost by passing over along
with the subliming ammonium halide. The process appears to be more electrical
than mechanical in nature. A space charge develops between the product and the
sublimate during sublimation. When the product particles are finely divided, they
jump vigorously and continuously as long as the ammonium halide sublimes. Indeed,
a slight tap on the vessel will cause considerable quantity of the product to leap to the
far end of the sublimation tube. Such jumping is negligible in samples where the
particle size is large. One obtains nearly quantitative yield from such samples.
(9) J. HAUBEN.J. BAEDLERand W. FISCHER, Ber. Dtsch. Chem. Ges. 69 B, 1772 (1936).
187
225
331
187
187
187
281
59
44
59
36
207
207
308
56
42
55
51
30.7
29.1
29.3
29.7
58.0
26.6
57.4
12.2
8.8
11.8
7.2
30.7
29.1
29.7
11.2
8.4
’ 11.0
10.2
2.0
YbCI3
LaBr3
SmBr3
EuBr3
YbBr3
La13
Ce13
Nd13
SmI2
EL&
Gd13
YbI3
PrC13
NdClJ
SmCIs
EuCI,
CeCl 3
LaCIj
Compd .
5.0
5.0
5.0
5.0
10.1
4.75
10.0
2.0
1.5
2.0
1.4
5 .o
5.0
5.0
2.0
1.5
2.0
m Moles
NHdX
lanthanide
metal
Wt. of oxide
w
m Moles
TABLE I.-DATA
3.26
16.4
26.0
28.6
28.4
51.4
20.6
47 .o
6.4
5.38
6.4
4.86
25.6
18.1
25.2
8.0
4.83
8.5
m Moles
halides
obtained
33
53.5
90
98 ~7
96
88.5
78
82
54
61.5
54
67.5
83
62 a3
85
70
59
78
Yield
(%)
99.8
100.1
99.2
99.8
99.8
99.6
100
99.4
99.8
99.7
99.6
99.7
100
99.2
99.7
99.5
Purity
(%)
ON ANYYDROUSLANTHANIDEHALIDES
White
White
Light green
Pink
White
Pale yellow
White
White
Light gray
Light gray
Light gray
Gray
Bright yellow
Light green
Yellow
Pale green
Light greenishyellow
Greenish-yellow
Colour
Cloudy
Clear
Clear
Clear
Slightly cloudy
Very slightly cloudy
Clear
Clear
Clear
Clear
Clear
Clear
Slightly cloudy
Clear
Slightly cloudy
Cloudy
Cloudy
Clear
Water solution
Preparation of anhydrous lanthanide halides, especially iodides
391
Data in Table 1 show that instead of the tri-iodides, the di-iodides of Sm and Eu
are obtained. Other experiments have shown that when the reaction temperature is
too high, instead of pure EuCI3, a mixture of EuCI2 and EuCI 3 is obtained. Thus
SmI3 and EuI3 can not be prepared by the ammonium halide method. It is doubtful
if any method is known which yields pure samples of these compounds.
The method described above is the only one known to the author which produces
nearly all the anhydrous lanthanide halides pure and in good yield by a relatively
simple procedure.