Inorganic Syntheses, VolumeI1
Edited by W Conard Fernelius
Copyright © 1946 by McGraw-Hill Book Company, Inc.
216
INORGANIC S Y N T H E S E S
The precipitate is finally washed with 12-1. portions of
water, centrifuged, and dried at 110" in an electric oven.
A yield of 35 g. of the hydrous P-1-hydrate is obtained from
100 g. of FeCI3-6Hz0. The process of settling in the later
stages is very slow and much time may be saved by the use
of a centrifuge.
Analysis
The amount of chloride in the sample is determined by
dissolving a weighed portion in warm, concentrated nitric
acid. After evaporation to remove excess acid and dilution
with water, the chloride is precipitated as silver chloride,
dissolved in ammonia, reprecipitated with dilute nitric
acid, and weighed in the usual manner. The iron(II1) in
the combined filtrates is determined by precipitating with
ammonia and is weighed as Fe2O3according to the standard
procedure. Typical analytical results give an Fe :C1 ratio
of 40:l.
References
1. BAUDISCH
and HARTUNG:
INORGANIC
SYNTHESES,
1, 185 (1939).
2. WEISERand MILLIGAN:J . A m . Chem. Soc., 67, 238 (1935).
3. WEISERand MILLIGAN:Chem. Revs., 26. 1 (1939).
69. HEXAMMINECOBALT(III) SALTS"
SUBMITTED BY JANNIH
BJERRlJLif AND JAMES
P. MCREYNOLDS$
CHECKED
BY ALFREDL. OPPECARD$
AND R. W. PARRY$
Hexamminecobalt(II1) sa.lts may be prepared by any of
three methods that depend on oxidation of cobalt(I1) ion
* Procedures for preparing most of these salts were originally submitted
by Dr. McReynolds, who was impressed by the simplicity of Dr. Bjerrum's
method. Shortly after the manuscript for Vol. I1 had been sent to the
publisher, similar procedures for three of these salts were submitted by
Dr. Bjerrum. Inasmuch as the method was developed by Dr. Bjerrum and
war conditions prevented his submitting the procedures a t a n earlier date,
the editors have taken the liberty of combining the two sets of directions
and presenting them as a joint effort of the two men.
t University of Copenhagen, Copenhagen, Denmark.
$ The Ohio State University, Columbus, Ohio; deceased.
$ University of Illinois, Urbana, Ill.
H E X A M M I N E C O B A L T ( I I I )S A L T S
217
in ammoniacal solution : (1) air oxidation, with formation
of the pentammine ion, which is converted to-the hexaml1
mine by heating with aqueous ammonia under.pre~sure;'-~,
(2) oxidation with an agent such as hydrogen p e r ~ x i d e , ~
iodine,5 potassium permanganate,6 lead d i ~ x i d e or
, ~ hypochlorite solutions;8 (3) oxidation in the presence of a
catalyst that allows equilibrium between the pentammine
and hexammine ions to be established at room temperature
and atmospheric pressure. These compounds may also
be prepared indirectly from other hexamminecobalt(II1)
salts.9,10
I n the best of the catalytic methods diamminesilver
is used as a catalyst.
ion12.13 or decolorizing
The method devised by J. Bjerruml* in which decolorizing
charcoal is the catalyst is simple, gives high yields of pure
product, and is not time-consuming. A high concentration of ammonium salt is sufficient to stabilize the hexamminecobalt(II1) ion, and the carbon serves only to establish
the equilibrium. Air is used as oxidant except when the
cobalt(I1) compound is slightly soluble in the ammoniacal
solution, as in the preparation of [ C O ( N H ~ ) ~ for
] B ~which
~,
hydrogen peroxide is preferable.
Procedure
A. HEXAMMINECOBALT(II1) CHLORIDE
4COc12
+ 4NH4Cl+
20NH3
+
0 2 +
4[Co(NH3)6]Cl,
+ 2HzO
Two hundred and forty grams (1 mol) of cobalt(I1)
chloride 6-hydrate and 160 g. (3 mols) of ammonium
chloride are added to 200 ml. of water. The mixture is
shaken until most of the salts are dissolved. Then 4 g. of
activated decolorizing charcoal* and 500 ml. of concentrated ammonia are added. Air is bubbled vigorously
* In order to obtain a rapid reaction, care must be exercised in the choice
of this catalyst. Charcoal from the center of a package has been found t.o
be much more effective than that from the top.
INORGANIC SYNTHESES
218
through the mixture until the red solution becomes yellowish brown (usually about 4 hr.).* The air inlet tube is of
fairly large bore (10 mm.) to prevent clogging with the precipitated hexamminecobalt(II1) salt.
The crystals and carbon are filtered on a Buchner funnel
and then added to a solution of 15 to 30 ml. of concentrated
hydrochloric acid in 1500 ml. of water; sufficient acid should
be used to give the entire mixture an acid reaction. The
mixture is heated on a hot plate to effect complete solution
and is filtered hot. The hexamminecobalt(II1) chloride is
precipitated by adding 400 ml. of concentrated hydrochloric acid and slowly cooling to 0". The precipitate is
filtered, washed first with 60 per cent and then with 95 per
cent alcohol, and dried at 80 to 100O.t Yield 230 g. (85
per cent). Anal. Calcd. for [ C O ( N H ~ ) ~ ]Co,
C ~22.0;
~ : C1,
39.8; NH3, 38.2. Found: Co, 22.0; C1, 39.8; NH3, 38.1.
B. HEXAMMINECOBALT(II1) NITRATE
+ 4NH4NO3 + 20NH3 +
4[Co(NH3)6I(NO3)3+ 2Hz0
[CO(NH3)6]C13+ 3HNO3 [ C O ( N H ~ ) ~ ] ( N+O3HC1
~)~
1. 4Co(NO3)2
2.
0 2 -+
-+
Method 1. Seventy-three grams of cobalt nitrate 6hydrate (0.25 mol) is dissolved in 100 ml. of water, and, in
the order mentioned, 80 g. (1 mol) of ammonium nitrate,
2 g. of activated charcoal, and 180 ml. of concentrated
ammonia (about 2.5 mols of NH,) are added. The solution is oxidized by air as specified in Procedure A. The salt
is washed with a little ice-cold water and is dissolved on a
steam bath in 1300 to 1500 ml. of water containing enough
nitric acid to give the mixture an acid reaction. After
*Care should be taken t h a t the bubbling is not too vigorous, as this
removes part of t h e ammonia from the solution. If this happens, the solution stays red instead of becoming yellow. Although more ammonia may
be added, the yield will be decreased somewhat.
t When the salt is dried at a higher temperature, it sometimes turns green.
The original color is restored by redissolving and reprecipitating with hydrochloric acid.
H E X A M M I N E C O B A L T ( I I IS) A L T S
219
removal of the carbon by filtration, the solution is treated
with 200 ml. of concentrated nitric acid and left to cool.
The precipitated salt is washed with water and alcohol and
dried at 100". Yield 77 to 79 g. (88 to 90 per cent). Anal.
Calcd. for [CO(NH,),](NO,)~:
Co, 17.0; NH3, 29.4. Found:
CO, 16.9; NHS, 29.4.
Method 2. The precipitate from the oxidation of
cobalt(I1) chloride (Procedure A) is dissolved in 1500 ml. of
water containing 15 to 30 ml. of concentrated nitric acid.
The carbon is removed and the salt precipitated with 450
ml. of concentrated nitric acid. The crystals are washed
with two 200-ml. portions of alcohol to remove excess acid
and dried at 100". Yield 103 g. (88 per cent). A solution
of these crystals gives only a slight turbidity with silver
nitrate.
C. 'HEXAMMINECOBALT(II1) BROMIDE
+
+
CoC03 2HBr -+ CoBrz HzO 4- COz
2CoBrz 2NH4Br 10NH3 H202 -+
2[Co(NH3)JBr3
+
+
+
+ 2Hz0.
Twenty-four grams (0.20 mol) of cobalt carbonate* is
added slowly to 100 ml. of 45 per cent hydrobromic
acid (0.80 mol). To the solution, 2 g. of activated charcoal and 120 ml. of concentrated ammonia (1.6 mols of
NH3) are added. The precipitate of cobalt(I1) salt that
appears is disrega.rded, and 40 ml. of 30 per cent hydrogen
peroxide (0.40 mol) is added slowly while the solution is
stirred. When the vigorous effervescence has ceased, the
main part of the cobalt(I1) precipitate has been converted
into the desired product. To complete the equilibrium
adjustment, the mixture is heated for 5 min. on a steam
bath and then left standing for 55 hr. The salt-carbon
mixture is filtered, washed with a little cold water, and
treated with 900 to 1000 ml. of water containing sufficient
* A cobalt determination must be made on the cobalt carbonate used if a::
accurate check on the yield of the complex salt is desired.
220
INORGANIC SYNTHESES
hydrobromic acid to give a slight acid reaction. The mixture is heated on the steam bath until all the salt is dissolved. To the hot solution is added 50 ml. of 45 per cent
hydrobronlic acid, and the reaction mixture is slowly
cooled to 0". The product is filtered, washed with icecold water, washed with alcohol, and dried at 100". Yield
about 64 g. (80 per cent). Anal. Calcd. for [CO(NH,)~]Bra: Co, 14.7; Br, 59.8; NH3, 25.5. Found: Co, 14.7; Br,
59.9; NH3, 25.3.
D. HEXAMMINECOBALT(II1) OXALATE
+
+
~ [ C O ( N H ~ ) ~ 3Na2C2O4
]C~~
4H20
[ C ~ ( N H ~ ) ~ I Z ( C Z ~6NaC1
~)~.~HZ~
+
Hexamminecobalt(II1) oxalate is prepared by adding a
soluble oxalate t o a solution of the ch10ride.l~ The salt
dried at 96" contains four mols of water. This precipitation is a quant,itative method for determining the amount
of hexamminecobalt(II1) ion in a mixture.
Properties
The hexamminecobalt(II1) salts are obtained as reddishbrown crystals, orange-yellow when finely divided. The
solubilities in water in mols per liter at 20" are: chloride,
0.26; nitrate, 0.052; sulfate, 0.020; oxalate (18"), 0.00069;
bromide (18"), 0.04. In liquid ammonia at -80" the
chloride forms a 6-ammoniate of the formula
[CO(NH3)6]Cl3*6NH3.
The oxalate is soluble in oxalic acid solution. A great
many double salts are formed. A detailed discussion of the
properties and formation of other salts appears in Gmelin.16
References
1. FREMY:
Ann. chim.phys., 131 36, 257 (1852).
2. JORGENSEN:
2. anorg. Chem., 17, 455 (1898).
3. LA^ and LARSON:
J. Am. Chem. SOC.,42, 2025 (1920).
4. MORGAN
and MAINSMITH:
ibid., 121, 1970 (1922).
TRIS(ETHYLENEDIA,VLINE)COBALT(NI)CHLORIDE 22 1
5.
6.
JORGENSEN:
J . prakt.
RIILLs:
Phil. Mag.;
Chem., [2] 23, 229 (1881).
[4] 36, 245 (1868).
7. B ~ u N Ann.,
:
142, 52 (1867).
8. JACOBSEN:
Overs. Danske Sclsk. Forh., 1899, 564.
9. Ref. 2, p. 457.
10. BILTZ:Z. anorg. Chem., 83, 178, (1914).
11. BILTZand BILTZ:(trans. by Hall and Blanchaid): “Laboratory Methods
of Inorganic Chemistry,” p. 175, John Wiley & Sons, Inc., New York,
1909.
12. Ref. 8, p. 575.
13. Ref. 10, p. 177.
14. BJERRUM:“Metal Ammine Formation in Aqueous Solution,” p. 241,
P. Haase and Son, Copenhagen, 1041.
15. SORENSEN:dissertation, p. 64, Copenhagen.
16. GMELIN: “Handbuch der anorganischen Chemic,” No. 58 B (Kobaltammine), pp. 46-72, Verlag Chemie G.m.b.H., Eerlin, 1930.
70. TRIS (ETHYLENEDIAMINE) COBALT(II1)
CHLORIDE
4C0C12
+ 8CzH4(NHz)z + 4C2Hj(n’Hz)z*HC1+
+ 2Hz0
0 2 4
4[Co(en),]C13
J. B. FIrORK*
CHECKED
BY JAMES
P. MCREYNOLDS~
SWXITTED B Y
Ethylenediarnine coordinates with metallic ions through
both nitrogen atoms. The five-membered chelate rings
that are thus formed are very stable. Many cobalt(II1)
ammines are converted by aqeuous ethylenediamine to
tris(ethylenediamine)cobalt(III) chloride. Thus, Jorgensen1 prepared the salt by heating [Co(NH3),C1]C12with
aqueous ethylenediamine. Grossmaii and Schuck2obtained
the salt by oxidizing a mixture of cobalt(I1) chloride,
ethylenediamine, and water. The method described below
has been developed from the latter suggestion.
Procedure
Sixty-one grams of 30 per cent ethylenediamine is partly
neutralized with 17 ml. of 6 N hydrochloric acid and the
* UrGversity of
Illinois, Urbana, Ill.
t The Ohio State University, Columbus, Ohio: deceased,