Solubility of potassium and sodium orthophosphates in ethylene glycol

Article abstract of DOI:10.1134/S1070427212050278

Solubility of potassium and sodium orthophosphates in ethylene glycol was determined.

Full text of DOI:10.1134/S1070427212050278

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 5, pp. 841−842. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.V. Kurzin, A.N. Evdokimov, V.S. Golikova, V.A. Fedorov, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 5,
pp. 842−843.
BRIEF
COMMUNICATIONS
Solubility of Potassium and Sodium Orthophosphates
in Ethylene Glycol
A. V. Kurzin, A. N. Evdokimov, V. S. Golikova, and V. A. Fedorov
St. Petersburg State Technological University of Vegetable Polymers, St. Petersburg, Russia
Received January 25, 2011
Abstract—Solubility of potassium and sodium orthophosphates in ethylene glycol was determined.
DOI: 10.1134/S1070427212050278
Phosphates of metals are used in various industries
(textile, cement, glass, and ceramic) and in everyday life,
including the use as components of cleaning agents, min-
eral fertilizers, structural materials, and food and fodder
additives. In the most widespread handbooks and separate
papers [1–5] there is only information about dibasic so-
dium phosphate solubility in methanol and ethanol. Data
on the solubility of acid and neutral orthophosphates of
alkali metals in other alcohols, glycols, cellosolves, and
glycerin are absent. It is known [6–13] that the alcoholysis
of weak-acid salts (carbonates, orthophosphates, sulfides,
and cyanides), of organometallic compounds, and other
derivatives of alkali metals, such as acetylenides, am-
ides, hydrides, nitrides, and azides, can be considered
as a mode of preparation of corresponding alcoholates,
whereas the alcoholysis of hydroxides is one of industrial
methods of producing potassium and sodium alcoholates:
In particular, the data on the alcoholysis of 10.8 wt parts
of sodium orthophosphate by 93.2 wt parts of ethylene
glycol at a temperature of about 100°С are given:
НОСН2СН2ОН + Na3PO4
= NaOCH2CH2OH + Na2НРО4.
(2)
The reaction duration is not specified. As a result the
authors have obtained a solution consisting of 2.7 wt parts
of sodium monoethylene glycolate, 0.6 wt parts of sodium
hydroorthophosphate, 5.5 wt parts of sodium orthophos-
phates, and 91.2 wt parts of ethylene glycol. In addition
the precipitate consisted of 4 wt parts of Na2НРО4. The
above-given data allow us to calculate that the “solubil-
ity” of Na3PO4 and Na2HPO4 in ethylene glycol (at joint
presence of these salts and sodium ethylene glycolate) at
a temperature of about 100°С is 6.93 and 0.66 g of a salt in
100 g, respectively. However the authors of patent [6] did
not specify a mode of analysis of solid and liquid phases,
moreover, it is doubtful that the precipitate consisted only
of Na2НРО4 and did not contain initial Na3РО4.
MnX + ROH = ROM + Mn–1HX.
(1)
Here M is an alkali metal; X = CO3, S, CN, OH, PO4,
C≡C(H), NH2, H, N3, N, R; R = an alkyl; n = 1–3.
The purpose of this work was to determine the solubil-
ity of potassium and sodium orthophosphates in ethylene
glycol at 30 and 197°С, and also to elucidate a possibility
of glycolates formation.
Thus, the term “solubility” for the specified reaction
systems is incorrect. Earlier distributions of components
over phases in methanolysis reactions of potassium hy-
droxide and carbonate and also in alcoholysis of sodium
sulfide under the action of various alcohols [9–11] were
determined. Furthermore it was found that the methano-
lysis of potassium hydrocarbonate does not occur [9]. It
was reported in the patent [6] that glycolates are formed in
reactions of orthophosphates, cyanides, and carbonates of
alkali metals with ethylene glycol and propylene glycol.
EXPERIMENTAL
Ethylene glycol (analytical grade) was rectified in
vacuum. Sodium and potassium orthophosphates (ana-
lytical grade) were used without additional refining and
dried within 2 h at 200°С.
841

842
KURZIN et al.
Solubility of potassium and sodium orthophosphates in ethylene
glycol
phates in ethylene glycol was determined. It increases
on increasing temperature and on passing from sodium
orthophosphate to potassium orthophosphate.
Liquid phase c
(2) In the systems Na3PO4-ethylene glycol and
K3PO4-ethylene glycol an acid-base equilibrium takes
place, which results in the formation of corresponding
ethylene glycolates.
omposition, g/100 g
System
Т, °С
ethylene
glycolate
M3PO4 M2HPO4
K3PO4/ethylene
glycol
30
4.34
9.65
3.47
7.33
0.42
1.14
0.36
0.85
6.62
4.05
5.80
3.12
ACKNOWLEDGMENTS
197
Na3PO4/ethylene 30
glycol
This work was financially supported by the Govern-
ment of St. Petersburg [grant for young candidates of
sciences of high schools (2010)].
197
Mixtures of a corresponding salt and ethylene glycol
were prepared by a gravimetrical method; the error of
measuring weight did not exceed 0.1 mg. A preliminar-
ily heated-up hermetically closed vessel with a weighted
sample was placed in a temperature-controlled cell,
where a specified temperature was maintained accurate to
±0.05o. The mixture was continuously stirred within 10 h
at the specified temperature. The duration of stirring was
determined in preliminary experiments. After the speci-
fied time a liquid phase was separated from a solid phase
using a glass filter (Chott filter) beforehand heated-up to
a temperature of the experiment. In the case of complete
salt dissolution a repeated experiment with a reduced
ratio of amounts of solid and liquid phases was carried
out.Asolvent was distilled off in vacuum from the liquid
phase up to a constant weight.Aresidual and a solid phase
were extracted with a mixture of benzene : 1,4-dioxane
= 5 : 1. In this case ethylene glycolates of alkali metals
are extracted [7, 8]; they were detected only in a liquid
phase.After removing a mixture of solvents the weight of
formed ethylene glycolates was determined. Contents of
acid and neutral sodium and potassium orthophosphates in
a solid phase were determined by acid-base titration with
thymolphthalein and bromocresol green indicators [14].
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The experimental data are given in the table. It shows
that the phosphate content in a liquid phase increases on
increasing temperature and on passing from sodium ortho-
phosphate to potassium orthophosphate. The amount of
ethylene glycolates formed at 197°С is less than at 100°С
[6], as the equilibrium in reaction (2) is shifted aside the
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CONCLUSIONS
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(1) The solubility of sodium and potassium orthophos-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 5 2012