Clathrate Formation in Tetraisopentylammonium Bromide-Water System

Article abstract of DOI:10.1023/A:1025611713712

Three polyhydrates of tetraisopentylammonium bromide with 38, 32, and 26 water molecules and also the dihydrate were found in the i-Pent ₄NBr-H₂O system.

Full text of DOI:10.1023/A:1025611713712

Russian Journal of General Chemistry, Vol. 73, No. 4, 2003, pp. 503 506. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 4, 2003,
pp. 537 540.
Original Russian Text Copyright
2003 by Aladko, Dyadin, Mikina.
Clathrate Formation
in Tetraisopentylammonium Bromide Water System
L. S. Aladko, Yu. A. Dyadin, and T. V. Mikina
Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences, Novosibirsk, Russia
Received April 16, 2001
Abstract Three polyhydrates of tetraisopentylammonium bromide with 38, 32, and 26 water molecules and
also the dihydrate were found in the i-Pent4NBr H2O system.
The system tetraisopentylammonium bromide
(i-Pent4NBr) water was previously studied by DTA
[1]. A polyhydrate was revealed, melting at 30.5 C
with decomposition into two liquid phases. Plate-like
crystals of this hydrate were isolated, and their anal-
ysis gave the composition i-Pent4NBr (38.07
0.16)H2O. However, thorough studies made for tetra-
isopentylammonium fluoride [2] and chloride [3]
showed the possibility of formation of three poly-
hydrates (1:38, 1:32, and 1:27) for both compounds.
Therefore, there were all reasons to expect that
i-Pent4NBr forms more than one clathrate hydrate also.
Furthermore, it is known [4, 5] that water can form a
series of clathrate frameworks close in energy and
often consisting of the same polyhedra. To gain a
better insight into this problem, we performed a de-
tailed study of the i-Pent4NBr H2O system.
fact that one of the solid phases (i-Pent4NBr) appeared
to be lighter than the equilibrium liquid phase, so that
it floated, and the second solid phase (NH4Br) re-
mained under the solution. The hydrate numbers of
the compounds were estimated as intersection points
of Schreinemakers paths (n) with the i-Pent4NBr H2O
axis using a program described in [7]. As a result, we
obtained the hydrate numbers 38.06 0.35 (n = 4),
32.28 0.21 (n = 11), 25.99 0.21 (n = 6), and 1.91
0.10 (n = 5).
Knowing the stability areas allowed isolation of all
the compounds formed in the system. Their hydrate
numbers and melting points are as follows: 38.26
0.38 (number of runs m = 3, mp 28.3 C), 32.24 0.25
(m = 5, mp 29.5 C), 26.02 0.36 (m = 3, mp 30.3 C),
and 1.95 0.20 (m = 3). These data are well consistent
with those obtained in studying the ternary system.
Crystals of all the polyhydrates differ from each other.
The compound 1:38 was isolated as plates or typical
feathers ; the hydrate 1:32, as tetragonal prisms; and
the hydrate 1:26 crystallized as fine isometric crystals.
In the case of clathrate hydrates of quaternary
ammonium salts, the fusibility curve mostly provides
insufficient information on the number and composi-
tion of compounds formed; even more so for the
system in hand characterized by the syntectic type of
the curve. The Schreinemakers method [6] is more
descriptive and reliable, allowing detection of all
compounds formed in the system and exact determina-
tion of their composition. Therefore, in this work we
used this method to study the ternary system
i-Pent4NBr NH4Br H2O at 15 C (see table and
Fig. 1). In this system, we found the crystallization
regions of three polyhydrates (1:38, 1:32, and 1:26)
and dihydrate of tetraisopentylammonium bromide,
anhydrous i-Pent4NBr, and NH4Br. We succeeded in
separating the crystallization regions of the polyhy-
drates after we extended their solubility curve to the
area where they are metastable. We determined the
eutonic points between the 1:26 polyhydrate and di-
hydrate and also between the dihydrate and i-Pent4NBr
(see table). Determination of the eutonic point
between i-Pent4NBr and NH4Br was facilitated by the
From the inflections in the liquidus, visual findings,
and DTA data, we determined the melting points for
all the compounds formed in the binary system i-Pent4
NBr H2O, despite the fact that for polyhydrates the
melting points are very close (Fig. 2).
The 1:38 and 1:32 compounds melt incongruently
at 28.3 and 29.5 C, respectively. The 1:26 hydrate
melts syntectically at 30.3 C. The dihydrate melts
incongruently at 37.7 C. Compared to the results ob-
tained in [1], thorough study of the system helped to
find not one, but three polyhydrates; among them, as
mentioned above, the hydrate 1:26 has the highest
melting point. The liquidus of the 1:38 hydrate is
somewhat distinguished: it is well consistent with the
extension of the fusibility curve of the 1:32 hydrate
towards the metastable region. It was observed that
the 1:32 hydrate is readily realized in the metastable
1070-3632/03/7304-0503$25.00 2003 MAIK Nauka/Interperiodica

504
ALADKO et al.
Solubility isotherm (15 C) in the system i-Pent4NBr
NH4Br H2O
region, and at room temperature ( 20 C), we were
able to obtain (in different weighing bottles) both the
1:32 hydrate and the 1:38 hydrate stable under these
conditions.
Liquid phase, wt%
Residue, wt%
Solid phase
i-Pent4NBr NH4Br i-Pent4NBr NH4Br
It is interesting that a practically close region of
phase separation is observed in the i-Pent4NBr H2O
system, which, in itself, is a rather rare phenomenon.
Furthermore, the phase separation region is situated
just over the clathrate hydrate crystallization areas, as
in some other systems [8]. In such cases, one of
possible reasons for the retrograde solubility of liquids
is clathrate formation in the liquid phase [8]. The
phase separation region was studied by the Alekseev’s
method [9] and also by the solubility method. As seen
from Fig. 2, the results obtained by these methods are
well consistent.
0.96
0.66
0.54
0.54
0.55
4.85
7.70
10.00
15.25
17.62
17.69
20.02
12.46
2.45
3.98 1: 38
4.46
10.08
1.82a
1.54a
1.58a
1.55
1.50
1.52
6.36a
10.75a
13.79a
16.27
16.70
17.02
17.52
19.84
20.67a
21.27a
24.38a
13.99
12.74
17.24
10.44
4.50
15.86
16.34
14.43
17.23
21.82
17.25
4.31
7.60
8.09
12.41
15.25
10.60 1: 32
10.89
13.10
12.35
9.97
Finally, three polyhydrates and a dihydrate of tetra-
isopentylammonium bromide are formed in the sys-
tem i-Pent4NBr H2O. The 1:38 and 1:32 polyhy-
drates are typical of quaternary ammonium salts [5].
The 1:38 hydrates form rhombic structures, while
1:32 hydrates, tetragonal structures [5, 10]. The 1:26
hydrates are less abundant. For tetraisopentylammo-
nium fluoride and chloride, the 1:27 hydrate was
found, forming a tetragonal lattice with space group
I41/a (a = 16.89 , c = 17.11 ) [2]. It is quite
possible that the hydrate shell frameworks in 1:26
and 1:27 hydrates are quite similar, but it is not
unlikely that these are two different clathrate struc-
tures.
1.64
1.53
2.42a
2.51a
4.55a
15.62
2.99a
2.23
0.75
0.97
2.37
2.67
17.40a
20.12
22.30
23.03
24.45
24.58
15.00
12.84
25.03
22.33
20.05
22.48
12.44
14.95
9.85 1: 26
11.79
14.40
13.09
3.93
25.19
50.89
10.31 1: 26 + 1: 2
3.86
1.91
1.14
1.01
1.01
25.31
29.65
31.00
33.79
34.52
55.36
43.69
13.33
58.03
26.27
10.45
15.76
26.83 1: 2
12.61
24.94
The results obtained allow some conclusions
about the effect of anions on clathrate formation in
the series i-Pent4NHlg H2O (Hlg = F, Cl, Br). All the
three salts form the same number of polyhydrates, at
least two of them having similar compositions (1:38
and 1:32) and structures. The relative stability of the
hydrates slightly changes in the series. Comparison
with similar series for tetrabutylammonium salts [3]
shows that the effect of anions in the series i-Pent4
NHlg H2O is considerably weaker, as demonstrated,
for example, by data on the melting points. In the
series i-Pent4NHlg H2O, the melting points of hy-
drates change only slightly (32.4 34.6, 29.5 29.8, and
28.3 30.3 C for the fluoride, chloride, and bromide,
respectively), while for tetrabutylammonium, the
melting point decreases from 27.4 to 9.5 C on passing
from the fluoride to the bromide. Presumably, this is
due to the fact that bulkier tetraisopentylammonium
cation exerts a stronger stabilizing effect on the
cavities in the clathrate frameworks, so that the effect
of anions is less pronounced on this background.
1.22
35.47
21.54
27.80 1: 2 +
i-Pent4NBr
0.87
0.86
0.82
36.59
37.81
39.61
15.96
22.34
20.02
31.02
29.63 i-Pent4NBr
31.90
0.94
40.49
23.51
0.49
31.26 i-Pent4NBr +
68.99 NH4Br
0.81
0.59
0.47
40.59
40.71
40.85
41.10
0.33
0.29
0.23
75.66
70.87 NH4Br
70.81
a
Metastable phase.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 4 2003

CLATHRATE FORMATION IN TETRAISOPENTYL...
505
i-Pent4NBr
4
80
60
3
2
1
20
H2O
20
40
60
80
NH4Br
wt%
Fig. 1. Solubility isotherm (15 C) in the system i-Pent NBr NH Br H O (circles and squares refer to the liquid phase and
4
4
2
wet residue, respectively. Dotted line shows the solubility of metastable phases). (1) i-Pent NBr (38.06 0.35)H O, (2) i-
4
2
Pent NBr (32.28 0.21)H O, (3) i-Pent NBr (25.99 0.21)H O, and (4) i-Pent NBr (1.91 0.10)H O (three-phase areas are
4
2
4
2
4
2
cross-hatched; triangles refer to eutonic points).
EXPERIMENTAL
peratures with stirring, and the salt concentration was
determined as described above. In DTA experiments,
the heating rate was 0.2 deg min (the temperature
was controlled to within 0.05 C). The phase separa-
tion region was studied by the solubility and Alekseev
methods.
1
Tetraisopentylammonium bromide was synthesized
by the Menshutkin’s reaction [11]. Equivalent
amounts of triisopentylamine and isopentyl bromide
were refluxed for 28 h in acetonitrile. To prepare a
clathrate hydrate, the product was recrystallized twice
from ethyl acetate and then three times from water.
Then the product was concentrated and dried in a
desiccator over P2O5. The main substance content was
determined by potentiometric titration with sodium
tetraphenylborate [11] to be 99.8 0.2 wt%.
The ternary system was studied by the Schreine-
makers method involving analysis of the liquid phase
and wet residue after equilibration. The time required
for establishment of the equilibrium (under me-
chanical stirring) was 4 6 h. The total bromide was
determined by titration with 0.03 N Hg(NO3)2 using
diphenylcarbazone as an indicator. Tetraisopentyl-
ammonium was determined as described above.
The fusibility curve was constructed using the
DTA data from [1] and DTA and solubility data ob-
tained in this work (these data are quite consistent).
In solubility measurements, an oversaturated aqueous
solution of a salt was kept for 4 7 h at various tem-
Crystalline samples were isolated at 10 15 C by
pressing between two sheets of filter paper. Then their
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 4 2003

506
ALADKO et al.
Compounds, Institute of Inorganic Chemistry, Si-
T, C
berian Division, Russian Academy of Sciences,
Novosibirsk, Russia) and with his direct participation,
for which the authors are grateful to him.
120
The work was performed in the framework of the
Federal Target Program State Support for Integration
of Higher Education and Basic Research in 1997
2000, part 144.6 of USC on Supramolecular Chem-
istry (project no. 274).
100
85.3 C
80
60
REFERENCES
1. Dyadin, Yu.A. and Kiseleva, L.S., Izv. Sib. Otd. Akad.
Nauk SSSR, Ser. Khim. Nauk, 1980, issue 1, no. 2,
p. 124.
l1 + l2
37.7 C
40
2. Lipkowski, J., Suwinska, K., Rodionova, T.V., Uda-
chin, K.A., and Dyadin, Yu.A., J. Inclusion Phenom.,
1994, vol. 17, no. 2, p. 137.
30.3 C
27.3 C
3. Dyadin, Yu.A. and Terekhova, I.S., Izv. Sib. Otd.
Akad. Nauk SSSR, Ser. Khim. Nauk, 1980, issue 4,
no. 9, p. 88.
20
0
38
32
0.1 C
26
4. Malenkov, G.G., Zh. Strukt. Khim., 1966, vol. 7, no. 3,
p. 331.
5. Dyadin, Yu.A. and Udachin, K.A., Zh. Strukt. Khim.,
20
40
60
80
100
1987, vol. 28, no. 3, p. 75.
i-Pent4NBr, wt%
6. Schreinemakers, F.A.H., Z. Phys. Chem., 1906,
vol. 55, p. 71.
Fig. 2. Phase diagram of the system i-Pent NBr H O.
4
2
7. Yurchenko, V.K. and Dyadin, Yu.A., Available from
VINITI, Moscow, 1975, no. 3115-75.
The numerals along the composition lines refer to the
hydrate numbers; rhombs and triangles show DTA data
obtained in this work and in [1]; circles and squares
represent points obtained from the solubility data and by
the Alekseev’s method; and l and l are the liquids rich
8. Nikolaev, A.V., Dyadin, Yu.A., and Yakovlev, I.I.,
Dokl. Akad. Nauk SSSR, 1966, vol. 170, no. 1, p. 110.
9. Alekseev, V.F., Zh. Ross. Fiz.-Khim. O va., 1877,
1
2
in water and organic phase, respectively.
vol. 9, p. 208.
10. Jeffrey, G.A. and McMullan, R.K., Prog. Inorg.
Chem., 1967, vol. 8, p. 43.
elemental composition and melting point were deter-
mined (visually in a thin-wall capillary).
11. Goerdeler, J., Quaternary Ammonium Compounds
(Houben Weyl), 1958, vol. 2, part 2.
ACKNOWLEDGMENTS
12. Smolyakov, B.S., Dyadin, Yu.A., and Aladko, L.S.,
Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk,
1980, vol. 4, no. 14, p. 66.
The figures were prepared using the programs
developed by E.V. Grachev (Laboratory of Clathrate
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 4 2003