Preparation of alkali-metal hypothiophosphates in an alcoholic solution

Article abstract of DOI:10.1134/S1070427211050041

A procedure was developed for preparation of lithium and sodium hypothiophosphates from the corresponding alkali-metal and phosphorus sulfides in ethanol. The possibility was explored for preparation of tin(II) hypothiophosphate in an alcoholic solution by an exchange reaction between sodium hypothiophosphate and tin(II) chloride.

Full text of DOI:10.1134/S1070427211050041

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 5, pp. 762−765. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.N. Svirskaya, T.G. Lupeiko, A.S. Pakhomov, E.S. Medvedeva, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 5,
pp. 732−735.
INORGANIC SYNTHESIS AND INDUSTRIAL
INORGANIC CHEMISTRY
Preparation of Alkali-Metal Hypothiophosphates
in an Alcoholic Solution
S. N. Svirskaya, T. G. Lupeiko, A. S. Pakhomov, and E. S. Medvedeva
Southern Federal University, Rostov-on-Don, Russia
Received February 18, 2010
Abstract—A procedure was developed for preparation of lithium and sodium hypothiophosphates from the
corresponding alkali-metal and phosphorus sulfides in ethanol. The possibility was explored for preparation of
tin(II) hypothiophosphate in an alcoholic solution by an exchange reaction between sodium hypothiophosphate
and tin(II) chloride.
DOI: 10.1134/S1070427211050041
Materials based on hypothiophosphate phases of M–
P–S systems, including tin(II) hypothiophosphate Sn2P2S6
and its analogs, possess a number of valuable properties
[1–5], thereby motivating high interest in synthesis and
study of the characteristics of these phases. Alkali-metal
hypothiophosphates M4P2S6 (M = Li, Na, K) are suit-
able for preparation of metal hypothiophosphates by the
exchange reaction [6, 7]
because of pressure increase. Attempts were made to
avoid this by increasing the temperature in an extremely
slow manner and creating a temperature gradient over
the ampule length (polytemperature synthesis), but this
does not entirely exclude the fire risk associated with the
above-mentioned procedure.
It was found earlier [13] that p- and d-element salts
can be synthesized in air from metal sulfides, sulfur, and
phosphorus. However, this procedure is fraught with con-
tamination of the target products with oxygen-containing
compounds. Also, no data were provided on the prepara-
tion of s-element hypothiophosphates.
2 MCl2 + Na4P2S6 = M2P2S6↓ + 4 NaCl.
The currently known procedures for preparation of
hypothiophosphate phases (in particular, of alkali-metal
hypothiophosphates) suffer from serious drawbacks.
The most extensive practical application among them is
found by the synthetic route involving the use of elemen-
tary substances from the M–P–S ternary systems and of
binary compounds formed in the M–P, M–S, and P–S
binary systems, as well as of these elementary substances
variously combined with the binary compounds [8]. To
prevent the reaction with water vapor and atmospheric
oxygen, the process is carried out in sealed ampules.
The synthesis temperature ranges from 350 (As2P2S7)
[9] to 950°С (GdPS4) [10], and the synthesis time, from
2 days (Sn2P2S6) [11] to 3 months (Co2P2S6, Ni2P2S6,
Mg2P2S2) [12]. However, the use of low-melting volatile
components (sulfur, phosphorus, phosphorus sulfides) in
a closed volume often results in the ampule destruction
Falius [14] suggested preparation of alkali-metal
hypothiophosphates in aqueous solutions from alkali-
metal sulfides and phosphorus chlorides. However, ex-
tensive application of this route is hindered by complex
procedures involved in preparation of the precursors, in
particular, phosphorus(III) chloride [15], as well as by
contamination of the resulting alkali-metal thiophos-
phates with oxidation and hydrolysis products.
Asynthetic route for alkali-metal hypothiophosphates
from alkali-metal and phosphorus sulfides in organic sol-
vents avoided quite a number of technological problems.
EXPERIMENTAL
A procedure was developed for preparation of so-
762

PREPARATION OF ALKALI-METAL HYPOTHIOPHOSPHATES
763
dium and lithium hypothiophosphates in a solution of
rectified ethanol and subsequent synthesis of tin(II)
hypothiophosphate by the exchange reaction with the
resulting Na4P2S6.
Precursors were alkali-metal and phosphorus sulfides.
As the initial phosphorus sulfide served a phase with the
conditional formula P4S8 which, according to the phase
diagram of the sulfur–phosphor system [16], is comprised
of a mixture of P4S9 and P4S7 phosphorus sulfides. This
phase was synthesized by heating of a thoroughly ground
mixture of sulfur and red phosphorus taken in the molar
ratio of 2 : 4 to 350–400°C in a stream of dry carbon
dioxide. Upon completion of the vigorous reaction the
resulting alloy was cooled and ground.
Sodium sulfide was prepared by dehydration with
acetone of its crystal hydrate Na2S·9H2O, and lithium
sulfide [17], by reduction of lithium sulfate with carbon
at 800°C.
Electron image of a sodium hypothiophosphate crystal grown
from an alcoholic solution. The scale division value is equal
to 0.25 mm.
Lithium and sodium hypothiophosphates were pre-
pared by the reaction of a saturated alcoholic solution
of each of the alkali-metal sulfide with a finely ground
phosphorus sulfide powder. Specifically, a P4S8 powder
was added to a saturated solution of the metal sulfides
in portions, under permanent vigorous stirring, until the
stoichiometric ratio was achieved. The reaction was ac-
companied by vigorous heat liberation. The solutions
were cooled to form gray-green Na4P2S6 and cream-
colored Li4P2S6 precipitates.
The resulting sodium and lithium hypothiophosphates
were analyzed for the content of sulfur and phosphorus
by the gravimetric procedure described in [18]. To this
end, each of the alkali-metal hypothiophosphates was
Table 1. Comparison of the ICSD data (no. 025357) with
the experimental X-ray diffractometric data for lithium
hypothiophosphate
ICSD
Experiment
2θ, deg
The X-ray phase analysis (DRON-2 diffractometer;
Cu radiation) showed that, by contrast to Li4P2S6, the
precipitated sodium hypothiophosphate was X-ray amor-
phous. It was recrystallized by dissolution in ethanol
under heating to 40°C and keeping at this temperature
for 2 h. Subsequently the system was slowly cooled, and
the resulting precipitate was kept in the mother liquor for
no less than 1 day to achieve maturation. This yielded
needle-like Na4P2S6 crystals having a length of 2–5 mm
(see figure). The crystals were carefully removed from the
vessel walls and weighed. The reaction between 0.32 g
of P4S8 and 0.26 g (100 ml of saturated solution) of Na2S
gave 0.52 g of a crystalline phase, with the target product
obtained in a 88–90 wt% yield.
2θ, deg
I
I
16.86
446
15.5
23.3
25.0
27.0
28.0
28.6
29.0
32.1
32.4
34.1
36.3
44.2
45.7
328.0
929.3
964.2
499.5
708.6
551.8
29.4
27.1
477
29.4
32.1
32.4
34.1
40.4
44.1
45.6
9
100
999
21
149.0
824.8
41.2
The X-ray diffraction analysis of the resulting crys-
talline phases revealed the formation of the target prod-
ucts containing trace impurities of alkali-metal sulfates
(Table 1). The elemental analysis data for the crystalline
phases additionally confirmed the formation of the target
products.
107
10
999.0
15.0
49
54.0
47.8
5
47.8
17.2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 5 2011

764
Table 2. Comparison of the ICSD data (no. 039232) with the experimental X-ray diffractometric data for tin hypothiophosphate
ICSD Experiment ICSD Experiment
2θ, deg 2θ, deg
SVIRSKAYA et al.
2θ, deg
I
I
2θ, deg
I
I
15.1
16.4
16.7
18.1
18.9
20.3
20.5
22.3
178
232
38
15.5
16.6
16.8
18.0
18.7
20.3
20.5
21.8
22.7
23.5
25.5
26.3
26.7
27.3
27.5
28.7
29.2
30.2
31.0
31.2
31.5
32.1
112
124
15
33.4
33.8
34.2
35.3
35.9
36.5
37.4
37.7
38.0
38.4
38.6
39.8
39.9
40.2
40.3
41.4
42.2
42.4
42.6
43.0
43.2
43.4
221
616
360
99
33.5
33.9
34.7
35.2
35.9
36.6
37.3
37.8
38.0
38.1
38.5
39.7
39.9
40.1
40.3
41.3
42.3
42.5
42.8
43.0
43.2
43.4
154
412
325.4
56
247
462
440
770
63
124
289
311.1
328.2
23
168
30
68.5
17.9
212
300
100
196
324
38
321
457
238
294
364
57
347
24
23.7
25.6
26.1
26.5
27.4
27.5
29.0
29.2
30.5
31.0
31.2
31.6
32.0
19
999
193
247
342
256
73
999
159.8
190
228
196
48
117
22
56
14
24
10
21
14
65
28.5
130
10
15
10
196
20
84
53
56
25
169
323
14
15
47
15
221
23.9
114
175
87
115
33.1
292
33.1
123
The resulting BaSO4 suspension was boiled in order to
coarsen the precipitate. Upon cooling, the precipitate was
filtered off on Blue Ribbon Filter ashless filter paper, burnt
in a muffle furnace, and weighed.
dissolved in boiling concentrated nitric acid. The dis-
solution was accompanied by conversion of phosphorus
and sulfur to Р+5 and S+6, respectively. The resulting
solution was neutralized with 15% ammonia to pH 9,
after which a magnesial mixture (3 g of MgCl2·6 H2O +
1.2 g of NH4Cl) was added to the solution to form a white
NH4MgPO4 precipitate. The latter was filtered off on Blue
Ribbon Filter ashless filter paper and subsequently burnt
in a muffle furnace, whereupon the resulting Mg2P2O7
was weighed. For determination of the sulfur content,
a saturated barium chloride solution was added to the
examined solution (upon separation of the phosphate).
Chemical analysis showed that, for all the products
obtained, the P : S molar ratio was close to 2 : 6 (1.97 :
5.95 for Na4P2S6 P : S and 1.94 : 5.93 for Li4P2S6).
The sodium hypothiophosphate synthesized was used
as precursor for preparation of tin(II) hypothiophosphate.
To this end, a saturated alcoholic Na4P2S6 solution was
added to a 0.1 M alcoholic SnCl2 solution under heat-
ing. To shift the equilibrium toward the reaction prod-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 5 2011

PREPARATION OF ALKALI-METAL HYPOTHIOPHOSPHATES
765
and Chalcohalides: Preparation and Properties), Kiiv:
Vishcha Shkola, 1983.
ucts, tin(II) chloride was taken in a slight (2%) excess.
Subsequent cooling of the system was accompanied by
formation of a brown-red precipitate which, based on its
X-ray diffraction pattern, was identified to be tin(II) hy-
pothiophosphate with a minor impurity of tin(II) sulfide
(Table 2). The resulting tin(II) hypothiophosphate served
as the base for vacuum thermal evaporation deposition
of thin (h = 2–10 μm) films. These films were character-
ized by relative dielectric permittivity (εт33/ε0 = 400) and
piezoelectric sensitivity at low frequencies under bulk
excitation [(5.5–5.7) × 10–7 V Pa–1]. Our data suggest that
the compound synthesized is suitable for the evaporation
deposition of films with properties no worse than those of
the films obtained from Sn2P2S6 which was synthesized in
vacuum-sealed ampules from elementary substances [19].
2. Gerzanich, E.I. and Fridkin, V.M., Segnetoelektriki tipa
АVВVIСVII (Ferroelectrics of АVВVIСVII Type), Moscow:
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3. Belyaev, L.M., Grekov, A.A., Zaks, P.L., and
Tatarenko, L.N., Akust. Zh., 1977, vol. 23, no. 5, p. 810.
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Ser. Fiz., 1964, vol. 28, no. 4, p. 681.
5. Vysochanskii, Yu.M. and Slivka, V.Yu., Izv. Akad. Nauk
SSSR, Ser. Fiz., 1987, vol. 51, no. 12, p. 2156.
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Allg. Chem., 1980, vol. 470, no. 11, p. 39.
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CONCLUSIONS
1997.
9. Wibbelmann, C. and Brockner, W., Z. Naturforsch. A, 1981,
(1)Aprocedure was developed for synthesis of lithium
and sodium hypothiophosphates suitable as precursors
for M2+ exchange reaction. Conditions were identified
under which stoichiometric lithium and sodium hypo-
thiophosphates can be prepared from alkali-metal and
phosphorus sulfides in an alcoholic solution in the form
of X-ray amorphous and crystalline phases.
vol. 36, no. 8, p. 836.
10. Rolland, Le, Molinie, P., and Cdombet, P., C.r. Acad. Sci.,
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Chem., 1973, vol. 396, no. 3, p. 271.
13. RF Patent 2089491.
(2) The sodium hypothiophosphate synthesized
was used for preparation, by an exchange reaction, of
tin(II) hypothiophosphate suitable for vacuum thermal
evaporation deposition of piezoelectrically active thin
films (h = 2–10 μm).
14. Falius, H., Z. Anorg. Allg. Chem., 1968, vol. 356, nos. 3–4,
p. 189.
15. Koryakin, Yu.V. and Angelov, I.Ch., Chistye khimicheskie
veshchestva (Pure Chemical Substances), Moscow: Khi-
miya, 1974.
16. Vincent, H., Bull. Soc. Chim. France, 1972, vol. 6, no. 12,
ACKNOWLEDGMENTS
p. 4517.
17. Handbook of Preparative Inorganic Chemistry: Guide
to Inorganic Chemistry, Brauer, G., Ed., New York:
Academic, 1963, vol. 2.
This study was financially supported by the “Scientific
and Scientific-Pedagogic Staff of the Innovative Russia”
Federal Target Program (State contract no. P-401).
18. Korostelev, P.P., Titrimetricheskii i gravimetricheskii
analiz v metallurgii (Titrimetric and GravimetricAnalyses
in Metallurgy), Moscow: Metallurgiya, 1985.
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