Indian Journal of Chemistry
Vol. 38A. September 1999, pp.966-968
The reaction of barium manganate with
acids and their precursors
Liszlo Kotai, Agnes Keszler, Janos Pato . Sandor Holly
Chemical Research Cente r, Institute of Chemistry.
Hungarian Acad emy of Sciences
H-1025, Budapest, Pusztase ri u. 59-67, Hunga ry
and
Kalyan K Banerji '
Department of Chemistry, J N V Universi ty,
Jodhpur 342 005, India
Received 30 November 1998; revised 4 Mal' 1999
A simpl e and easy preparative route to obtain permangani c ac id
and perma nga nate salts from barium manganate and sulphuric ac id
is described. Sulphuri c ac id reacts with bari um manganate to produce sparingly soluble bariulll sulphate and well-soluble permanganic ac id or bari ulll permanganate, these in turn can be usee! to prepare ot her metal perm anga nates.
Perman ga nates are wide ly used in organic sy ntheses as
se lective oxidizing agentsl . Barium permanganate is su itable for selective o xid at ion itsclf2-6 and can be used as
starting materi a l for the synthesis of seve ral other metal
pe rmanganates als0 7.X• The reaction o f permallganic aci d
with oxides, hydroxides or carbonate' yields a lot of cIeri vati ves') .
Synthesis of barium pennanganate starts from bari um
man ganate which itse lf is o btain ed in pure form from
potassi um perman ganate and water soluble barium salts .
Reported meth ods for the conversion of barium man ganate to the corresponding permanganare are comp l icated
procedures. In thi s note, the synthesi s of permanganic
acid and barium permanganate and their use in the synthes is of several other metal permanganates are reported .
Experimental
Analytical grade reagents (A ldrich) and double-distilled water were used throughout. The IR spectra were
obtained in nujolmull with NICOLET 205 FT-IR spectrometer and by diffu se reflectance tec hni que in KBr with
NICOLET 170SX spectrometer in the range of 400-4000
c m· l. rcp measurements we re made with Atomscan 25
(Thermo Jarral Ash) spectrome ter. X-ray powder dif-
fraction data were collected on a Phillips PW 3710
diffractometer, with a Cu monochromator.
Synthesis oj barium manganate (VI)
KMn04 (15.8 g) was dissolved in 300 ml of water,
then BaCI 2 .2Hp (24.9 g dissolved in 100 ml of wate r),
KOH (56 g dissolved in 100 ml of water) and KI (2.0 g
di sso lved in 20 ml of water) were added with vigorous
stirring. The mixture was boiled for 15 min, cooled,
filtered, and washed. The permanganate-free product was
dried at 105° C for I h, then the traces of water were
removed by azeotropic distillati on with benzene (yield
- 100%). Analysis (found/calc. fo r BaMn0 4 ): Ba 53.69/
53 .59%; Mn 21.40121.44 %.
Synthesis ojperman ganic acid
To barium manganate (2.56 g, 0 .0 I mol ) suspended
in 50 ml of di stilled water, su lphuric acid ( 100 ml , 0 . 1
mol) was added with stirring. The stirrin g was continued for I h. Th e reaction mixture was filte red and perman ganic ac id was titrated with NaOH potenti ometrically usin g a g lass e lectrode (PH 5.5 ). Th e product, sodium permanganate trihydrate, was crystall ized and identifi ed by IR spectroscopy; yie ld - 100%.
SYllthesis of barium permangana te
Bariu m man ganate (2. 56 g, 0.01 mol ) was suspended
in 100 ml of di still ed water. Then sulphuric acid (55 ml ,
0 . 1 mol ) was added over I h with slow stirring and then
refluxed for 15 min. The reaction mixtu re was filte red
and concentrated while barium perman ganate c rysta llized (yi e ld: 0.7 g), analysi s [found/calc. for Ba(Mn04)2]:
Ba 36.57/36.6 1% ; Mn 29.30129 .28 % .
Reaction of barium l1Iangana fe with sodium hydrogen
carbonate
Barium manganate (2.56 g, 0.0 I mol) was suspended
in 100 ml distilled water and calcul ated amounts of
NaHC01 (Ba:Na = I :0.75, I: I , I: 1.34 mol) was added .
The mixture was slowly stirred for I h a nd then refluxed
for 30 min . The reaction mixture was filtered and crysta lli zed. According to TR spectroscopy a nd X-ray
diffractometry, th e prod uct s con tai ned Ba(Mn0 4)2'
NaMn04 and Na 2CO, in di fferent ratios.
NOTES
Reaction of barium manganate with ammonium sulphate
To barium manganate (2.56 g, 0.01 mol), suspended
in 100 mol distilled water, was added ammonium su lphate (1.24 g, 0.0 I mol). The reaction mixture was stirred
for I h and then refluxed for I h. The mixture turned
dark violet and intense odor of ammonia was obtained .
The reaction mixture was filtered , concentrated and crystallized. According to IR spectroscopy the water-soluble
product was ammonium permanganate. Even if 2/3
amount of ammonium su lphate used, the on ly product
formed, under simi lar conditions, was ammonium permanganate.
Results and discussion
Synthesis of barium manganate in alkalin e medium
from potassium permanganate and barium chloride in
the presence of an alkali iodide is a well-known reaction
(I) . It results in the fornlation of insoluble barium manganate, which can be obtained in dry form after
azeotropic distillation of water with benzene.
6 KMnO, + 6BaCI 2 + 6 KOH + KI
~
BaMn04 + 12 KCI
+ KIO, + 3 Hp
.. ..( 1)
Unstable manganic acid is formed when barium manganate is treated with sulphuri c or carbonic acid (2) . It
disproportionates to permanganic ac id and mangan ese
dioxide (3) .
... (2)
where X = S04 or CO,
.. . (3)
967
Table 1- Comparison of effecti ve charge values and acidity of some
inorganic oxoacids '4
8,,1
Oxoacid
811
HlS04
+0.38
HMn04
HlMnO.j·
+0.37
+0.37
HlCO J
+0.39
8,/
8x
-0.46
-0.36
+0.88
1.125
-0.53
-0.46
+1 .56
1.114
-0.52
-0.42
+1.42
1.106
-0.50
-0.42
+0.67
0.965
<jl
• Our calculation
sulphuric acid. The ionic character of the hydroxy Is
(8i8o) are nearly similar in manganic and permanganic
acids but the polarizing effect of the central atom is higher
in permanganic acid . Consequently manganic ac id is
easily formed from barium manganate and sulphuric acid
due to the hi'gh acidity of su lphuric acid as well as the
insolubility of barium su lph ate. Carbonic acid being
weaker than manganic acid, the main driving force of
the reaction is the formation of insoluble barium carbonate. However, it is an equilibrium process and dissolution of barium carbonate in manganic acid takes place.
Manganic acid disproportionates to permanganic acid
and manganese dioxide (3). This reaction (log K = 58)
takes place comp lete ly in acidic, neutral or slightly alkaline media" .
Due to these facts permanganic acid is formed quickly
from barium manganate and SUlphuric acid via disproportionation of manganic acid (5). Thus this method is
suitable for the preparation of permanganic acid .
3 BaMn04 + 3 H2S04
~
2 HMn04 + 3 BaS04 + Mn02 + 2 Hp
.. . (5)
.
Dissociation constant of manganic acid has not been
determi ned so far. In order to explain the mechani sm of
these reactions, the relative strengths of the acids mu st
be known. To estimate them , a method published earli er
has been used l4 . Effective charges of the atoms of manganic acid and <p constants which characterize the acid
strength IS were calculated using relation (4) .
.. . (4)
where <p means the acid strength, 8H' 80 and 8x mean the
relative charges of the H,O, and X(S,C or Mn) atoms
respectively. The results are presented in Table I .
The data showed that manganic acid is a stronger acid
than carbonic acid but is weaker than permanganic or
Permanganic acid being a relatively strong acid re·acts easily with metal oxides, hydroxides or carbonates.
This method can be used to synthesize any permanganate.
T he analogous reaction between barium manganate,
water and carbon dioxide yield on ly very small amount
of manganic acid as expected from the relative strength
of the acids. Consequently longer time is required to
obtain a sign ificant amount of permanganic acid. Barium
carbonate is soluble in permanganic acid (latter be ing a
stronger acid) and this reaction has been reported as a
method of preparation of barium permanganate lO. 12 but
this method is less favourable than the new meth od reported here.
968
INDIAN J CHEM, SEC. A , SEPTEMBER 1999
To understand the reaction of barium manganate with
carbonic acid (2), it was considered essential to study its
reaction with sodium hydrogencarbonate. NaHCO, generates carbonic acid in boiling solutions which can form
barium permanganate as per reaction (2)
... (6)
While NaHCO, is a source of carbonic acid at slightly
alkaline pH, ammonium sulphate behaves as a slightly
acidic sulphuric acid precursor (8).
.. . (8)
The reaction of sulphuric acid and BaMn04 results in
the formation of permanganic acid. The e nd product of
the reaction of permanganic acid and ammonium hyd roxide is ammonium permanganate.
Equiv a lent amounts of ammonium s ulphate and
barium manganate yield 2/3 mol ammonium permanganate while ammonia is evolved. Using 2/3 mol of ammonium sulphate, the ex pected product is barium permanganate (in analogy with sulphuric aci d) but in practi ce ammonium permanganate was the product. P ro bably, manganic ac id reacts rapidly w ith am moni a before
anything e lse ca n happe n. Alternative ly, a mm onium
manganate mi ght be formed as an intermedi ate foll owed
by its disproportionati on.
Sodium carbonate can be detected by IR spectroscopy.
The reaction of barium permanganate and sodium carbonate yields barium carbonate and sodium permanganate trihydrate. When the mo lar ratio of the reactants is
I : I , the main product is barium permanganate and a small
amount of sodium permanganate trihydrate is formed.
Similar results are obtained when an excess of barium
manganate is used. However, an excess of NaHCn,
( I: 1.34) enhances the reaction bet ween barium permanganate and sodium hydroge ncarbonate and th e main
product is sodium permanganate trihydrate while barium
permanganate is the min or by-p roduct.
Since permanganic acid is stronger acid than man ganic ac id , in the presence of less than one equiva lent of
sulp huri c acid , permanganic ac id form ed reacts with
barium man ganate to produce barium permallganate and
man gani c acid. The latte r disproportionates to manganese dioxide and permanga nic ac id . Barium perma nganate is formed [reaction (7)] in the presence of2/3 equivalent of sul phuri c acid. Therefore, pure barium pe rmanga nate can be obtained by treatin g sul phuric acid with
an excess of barium manganate . Unreacted barium l11anganate can be easily removed by fi ltration .
4
. .. (7)
5
6
7
Due to extr~ln~ insolubility of barium sul phate when
bariu m permanganate reac ts with metal sul pha te:-. , th e
exchange reac ti on result s in th e formati on of metal permanganates. The so lubility produ ct or some of the hi ghl y
insolubl e sulph ates is: BaSnl' 1.07 x 10-1°; Pb50. 1.82
"
x IO-~ ; Sr504 , 3.44 x 10-7 ; Ag}S04' 1.20 x 10 ' and CaSn
,
l
5
6. 10 x 10- . It can be see n that even lead sulph ate is
almost 100 times more soluble than barium sulphate.
Consequently, the exchange reacti on in each case is practicall y complete.
.. (9)
3 (NH)!MnO. --7 2 N H. MnO. + 2 Hp + M n02 + 4 NI-! ,
... ( 10)
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