Solubility of Potassium Carbonate and Potassium Hydrocarbonate
Andrew Yu. Platonov,* Andrey N. E vdokimov, Alexander V. K urzin, and Helen D. Maiyorova
Organic Chemistry Department, Saint Petersburg State Technological University of Plant Polymers,
4 Ivana Chernykh, Saint Petersburg, 198095 Russia
The solubility of potassium carbonate in methanol and the acid-base interaction of these compounds
with each other have been considered. The reaction results in the formation of methoxide and
hydrocarbonateof potassium. Thereported values on thesolubility of potassium carbonatediffer essentially
from the data described in the literature. The solubility of potassium hydrocarbonate in methanol has
also been determined.
The solubilities of potassium carbonate in alcohols as
well as other carbonates have been studied previously.1-3
However, the authors of the papers did not take into
account the possible reaction between carbonate of alkali
metal as the base and alcohol as the acid
where M is an alkali metal and R is an alkyl group.
Loder and Lee4reported the formation and the recovery
of alkoxides according toeq1 for thefirst time. They offered
the process for the preparation of potassium methoxide
wherein 8.6 parts of K2CO3 and 94.6 parts of CH3OH
reacted at 20 °C for 6 h. Thesolid KHCO3precipitated from
a reaction mixture was filtered out. The remaining carbon-
ates were separated by evaporating methanol from the
solution, and then thecarbonates precipitated werereadily
filtered from the saturated potassium methoxide solution.
This latter solution may be further evaporated to obtain
solid potassium methoxide.
Studying the reactions of diethyl phosphite with elec-
trophiles in the K2CO3/C2H5OH system, we established the
formation of potassium ethoxideafter stirring of potassium
carbonate with ethanol using a titrimetric method.5
In thepresent paper, thesolubility of K2CO3in methanol
was determined in view of the above interaction. In
addition, the distribution of all components in the K2CO3/
CH3OH system was investigated under the conditions of
phase and chemical equilibrium. The solubility of KHCO3
in anhydrous methanol was also determined.
E xperimental Section
R eagents. As far as possible, anhydrous chemicals were
used. After dehydration, themethanol obtained from Merck
was stored above molecular sieves type 3A. The water
content in the methanol was controlled by the GC method
and did not exceed 0.02 mass %. Potassium carbonate and
potassium hydrocarbonate obtained from Aldrich (Reagent-
PlusTM) had a purity of 99.99 mass %. Before the experi-
ment, the potassium carbonate was warmed to 120 °C for
Procedure. The equilibrium concentrations of the com-
ponents of K2CO3/CH3OH and KHCO3/CH3OH systems
were determined using the titrimetric method. For this
purpose, a mixture of the appropriate carbonate (a known
mass of sample from 2.8 to 6.8 g) and 10 mL of methanol
was continuously agitated within 6 h in a temperature-
controlled cell at either (25 ( 0.05 °C) or (35 ( 0.05 °C).
Then the suspension was passed through a porous glass
filter under pressure. The solid and liquid phases were
treated with water separately. The concentrations of
K2CO3, KHCO3, and CH3OK were determined by hydro-
chloric acid solution using phenolphthalein and methyl
orange solutions as the indicators. Potassium methoxide
was titrated as a strong KOH base that was formed from
CH3OK as a result of a hydrolysis (see eq 2).
This acid-base titration with recording of two points of
equivalence allowed us to determine jointly K2CO3 and
KOH, as well as K2CO3and KHCO3.
Analogously, the K2CO3/CH3OH system was analyzed at
30, 40, and 45 °C.
R esults and Discussion
The mixture of potassium carbonate and methanol is a
heterogeneous system at a K2CO3/CH3OH ratio greater
than 30 g/100 g. The analysis of the liquid phase of this
system showed the presence of K2CO3, K HCO3, and
CH3OK, which are formed according to eq 1. The concen-
trations of these compounds under the conditions of the
thermodynamic equilibrium are presented in Table 1.
Only twocomponents, namely potassium carbonate and
potassium hydrocarbonate, were found in the solid phase
of the heterogeneous K2CO3/CH3OH system. The absence
of potassium methoxide in the solid phase was confirmed
in a separate trial. After the suspension was filtered, the
precipitate was extracted by dry benzene, the solvent was
removed in a vacuum, and the residue was treated with
water and analyzed by titrimetry (see Experimental Sec-
tion). No strong base was discovered.
Thequantities of potassium hydrocarbonatefound in the
solid phase were 6.87 g/100 g methanol and 6.18 g/100 g
* To whom correspondence should be addressed. E-mail: chemist@
ROH + M2CO3) ROM + MHCO3
CH3OK + H2O ) CH3OH + KOH (2)
1175J . Chem. Eng. Data 2002, 47, 1175-1176
10.1021/je020012v CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/29/2002
methanol at 25 and 35 °C, respectively. This is more than Download full-text
99% of the total KHCO3quantity generated according to
eq 1. The KHCO3quantities found both in the liquid and
the solid phases corresponded to the CH3OK quantity
revealed in the liquid phase.
Such a distribution of potassium hydrocarbonate be-
tween the solid and liquid phases promotes the shifting of
equilibrium 1 toward the formation of reaction products
according to Le Chatelier’s principle. This is confirmed by
the temperature dependence of the component composition
of the K2CO3/CH3OH system as presented in Figure 1.
Obviously, the concentration of the dissolved potassium
hydrocarbonate will increase with rising temperature so
that the rate of the reverse reaction increases and the
concentration of potassium methoxide decreases, accord-
When the values of the solubility of K2CO3in methanol
are compared with those known from the literature, it is
apparent that neglecting the interaction of K2CO3 with
CH3OH will result in toohigh values. In fact, the solubility
of potassium carbonate reported2is more than 6 g/100 g of
methanol at 25 °C; we measured a value approximately
four times lower (see Table 1). It is necessary to note that
thesum concentration of thedissolved potassium carbonate
and potassium methoxideaverages 6.4 g/100 g of methanol.
The authors of the cited papers used the gravimetric
method. These earlier values represent the alkaline equiva-
lents of the three reaction participants, expressed as
The authors4investigated the composition of the K2CO3/
CH3OH system. The values of solubility reported in their
paper equal 3.11, 3.11, and 0.96 g/100 g of methanol at 20
°C for K2CO3, CH3OK, and KHCO3, respectively. These
data are compared to those obtained in the present study
except for the solubility of KHCO3, which is more than 100
times higher. Unfortunately, the authors4failed to report
on the analytical procedure used. Moreover, it is doubtful
that the solid phase of the K2CO3/CH3OH system consists
Since methanol is both the solvent and the reactant in
the K2CO3/CH3OH system, the term “solubility of potas-
sium carbonate in methanol” is not precise. Probably, the
composition of the K2CO3/CH3OH system is mainly deter-
mined by the thermodynamics of the potassium carbonate
In contrast, the mixing of potassium hydrocarbonate
with methanol (up to the temperature 35 °C) is not
accompanied by thereaction of thesecomponents according
to eq 3.
Only KHCO3was found both in the liquid and in the
solid phases. The solubility of KHCO3is 0.018 g/100 g of
methanol and 0.038 g/100 g of methanol (at 25 °C and 35
We are grateful to Dr. Gunter Fuhrmann for helpful
Received for review J anuary 14, 2002. Accepted May 27, 2002. This
work was supported by grants for young scientists obtained from
the government of Saint Petersburg (M-00-2.5K-436) and the
government of Russian Federation.
L iterature Cited
(1) Stenger, V. A. Solubilities of Various Alkali Metal and Alkaline
Earth Metal Compounds in Methanol. J . Chem. Eng. Data 1996,
(2) Frankforter, G. B.; Frary, F. C. Equilibria in Systems Containing
Alcohols, Salts and Water, Including a New Method of Alcohol
Analysis. J . Phys. Chem. 1913, 17, 402-473.
(3) Harner, R. E.; Sydnor, J . B.; Gilreath, E. S. Solubilities of
Anhydrous Ionic Substances in AbsoluteMethanol. J . Chem. Eng.
Data 1963, 8, 411-412.
(4) Loder, D. J .; Lee, D. D. Preparation of Alkali Metal Alkoxides.
U.S. Patent 2,278,550; 7.04. 1942; Chem. Abstr. 1942, 36 (16),
(5) Platonov, A. Yu.; Sivakov, A. A.; Chistokletov, V. N.; Maiorova,
E. D. Transformations of Electrophilic Reagents in a Diethyl
Phosphite-Potassium Carbonate-Ethanol System. Russ. Chem.
Bull. 1999, 48, 367-370.
T able 1. Concentrations of the Components in the
K2CO3/CH3OH System (grams per 100 g of methanol)
1.61 ( 0.09a
2.01 ( 0.15a
0.0121 ( 0.0009a
0.0341 ( 0.0015a
4.82 ( 0.12a
4.37 ( 0.18a
a(3 std dev.
F igure 1. Temperature effect on the concentrations of potassium
methoxide and potassium hydrocarbonate in methanol.
KHCO3+ CH3OH ) CH3OK + CO2+ H2O (3)
1176J ournal of Chemical and Engineering Data, Vol. 47, No. 5, 2002