Synthesis, molecular structure, and vibrational spectra of tetrakis(2-hydroxyethylammonium) chloride and its triethanolamine precursor and metabolite

Article abstract of DOI:10.1134/S1070363214100065

A unique one-stage synthesis of tetrakis(2-hydroxyethylammonium) salts, precursors of new hypervalent silicon compounds, has been developed. The vibration spectra of tetrakis(2-hydroxyethylammonium) chloride and its triethanolamine precursor and metabolite have been studied by IR spectroscopy and quantum chemistry. Analysis of alterations in the modes with increasing number of HOCH₂CH₂ groups has been performed.

Full text of DOI:10.1134/S1070363214100065

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 10, pp. 1904–1908. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © G.S. Buslaev, I.S. Ignat’ev, N.G. Tyurnina, T.A. Kochina, 2014, published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 10,
pp. 1624–1628.
Synthesis, Molecular Structure, and Vibrational Spectra
of Tetrakis(2-hydroxyethylammonium) Chloride
and Its Triethanolamine Precursor and Metabolite
G. S. Buslaeva, I. S. Ignat’evb, N. G. Tyurninaa, and T. A. Kochinaa
a Grebenshchikov Institute of Silicate Chemisry, Russian Academy of Sciences,
nab. Makarova 2, St. Petersburg, 199034 Russia
e-mail: t-kochina@mail.ru
b St. Petersburg State University, St. Petersburg, Russia
Received May 26, 2014
Abstract—A unique one-stage synthesis of tetrakis(2-hydroxyethylammonium) salts, precursors of new
hypervalent silicon compounds, has been developed. The vibration spectra of tetrakis(2-hydroxyethyl-
ammonium) chloride and its triethanolamine precursor and metabolite have been studied by IR spectroscopy
and quantum chemistry. Analysis of alterations in the modes with increasing number of HOCH2CH2 groups has
been performed.
Keywords: triethanolamine, tetrakis(2-hydroxyethylammonium) chloride, molecular structure, vibration spectra
DOI: 10.1134/S1070363214100065
Organic derivatives of triethanolamine are of parti-
cular interest among atranes. Triethanolammonium
salts of protic acids [HN(CH2CH2OH)3]+X– (prota-
tranes [1]) have an endo atrane structure and are much
more bioactive [2, 3] than their precursor and
metabolite triethanolamine, as well as acids HX, which
are widely used in medicine and agriculture. Further
research on compounds of this class resulted in the
development of new medicines [4]. Later Walker and
Bruce suggested compounds with flexible hydroxy-
alkyl groups in the cation to be applied as ionic liquids
capable to dissolve, stabilize, and activate enzymes
[5, 6]. Tris(hydroxymethyl)aminomethane (Tris) added
in even small amounts to various ionic liquids much
enhanced the activity of horseradish peroxidase [7].
An even stronger effect can be obtained if to increase
the number and flexibility of hydroxyalkyl substituents
in the ammonium cation. The activity of enzymes
of previously unknown hypermetallatranes, in
particular, hypersilatranes.
Aimed at preparing tetrakis(2-hydroxyethyl-
ammonium) chloride, we have studied the reaction of
2-chloroethanol with triethanolamine. The reaction
was performed under reflux for 24 h in the absence of
a solvent, as well as in different solvents (butanol,
dioxane, acetonitrile) and at different reagent ratios.
However, we failed to obtain tetrakis(2-hydroxyethyl-
ammonium) chloride by this procedure. The reaction
yielded no other products but chloroprotatrane
[NH(CH2CH2OH)3]+Cl–. A similar reaction of trietha-
nolamine with iodoethanol in an open reaction system
resulted too in an exclusive formation of iodoprota-
trane [9]. Tetrakis(2-hydroxyethylammonium) chloride
could only be prepared by the procedure described in
[10]. However, also herethe major reaction product
was chloroprotatrane (as a powder insoluble in
methanol). The formation of chloroprotatrane is due to
a high proton affinity of the triethanolamine nitrogen;
as a consequence, the latter abstracts proton from the
2-chloroethanol hydroxyl (Scheme 1).
in
a
tetrakis(2-hydroxyethylammonium) chloride
[N(CH2CH2OH)4]+Cl– ionic liquid was 30–240 times
higher than in other ionic liquids [8]. On the whole, the
reactivity, molecular and stereoelectronic structure, as
well as bioactivity of this class of compounds have
never been studied. Moreover, tetrakis(2-hydroxy-
ethylammonium) salts can be considered as precursors
Possibly, tetrakis(2-hydroxyethylammonium) chlo-
ride obtained by the latter procedure is a secondary
1904

SYNTHESIS, MOLECULAR STRUCTURE, AND VIBRATIONAL SPECTRA
1905
Scheme 1.
Cl–[N(CH2CH2OH)4]+
N(CH2CH2OH)3 + ClCH2CH2OH
Cl–[NH(CH2CH2OH)3]+ + C2H4O
reaction product of chloroprotatrane with ethylene
oxide in a closed system under increased pressure.
Such chemical reaction has been described in a number
of patents [11].
have studied its structure and vibration spectra and
compared them with those of triethylamine. The
equilibrium structures of triethanolamine and tetrakis-
(2-hydroxyethyl)ammonium
[N(CH2CH2OH)4]+,
optimized at the B3LYP level with the aug-cc-pVTZ
basis set (including diffuse functions), are shown in
Figs. 1 and 2. The structure of monomeric
triethanolamine (Fig. 1a) belongs to the C3 point
group. The feature of this structure is that the hydroxy
groups of each of the HOCH2CH2N “blades” form
hydrogen bonds with each other with the O···H
distance of 2.023 A.
We suggested that the yield of tetrakis(2-hydroxy-
ethylammonium) chloride could be increased by
introducing ethylene oxide to the closed reaction
system. Therefore, before reaction varied quantities of
ethylene oxide were dissolved in a cold 2-chloro-
ethanol or its mixture with methanol. The triethanol-
amine–2-chlotoethanol–ethlene oxide molar ratio was
1.01 : 1 : (0.15–0.50). The weight fraction of methanol
in the reaction mixture was 30%. In view of the fact
that tetrakis(2-hydroxyethylammonium) chloride is
highly sensitive to moisture, after the reaction per-
formed with no solvent the required quantity of
methanol was added to the reactor to dissolve the
reaction product. When ethylene oxide was added
(even in a very small quantity), no precipitation of
methanol-insoluble chloroprotatrane was observed.
Tetrakis(2-hydroxyethylammonium) chloride was
recrystallized from ethanol taken in a quantity double
the weight of the methanol solution. The recrystallized
product was dissolved in methanol, and its concentra-
tion in the solution was determined by chloride
gravimetry. The yield of tetrakis(2-hydroxyethyl-
ammonium) chloride after recrystallization, calculated
per 2-chloroethanol in the initial methanol solution,
was 73%. According to X-ray diffraction data, tetrakis
(2-hydroxyethylammonium) chloride has several
polymorphic modifications which are likely to have
quite different melting points. The salt starts to melt at
80°С but does not liquefy completely until it starts to
decompose. Derivatographic analysis (heating rate
2.5 deg/min) showed that tetrakis(2-hydroxyethylammo-
nium) chloride is a fairly thermally stable compound.
It starts to decompose at about 200°С. Decomposition
sharply accelerates with temperature. When thermal
treatment of tetrakis(2-hydroxyethylammonium) chloride
is performed using an oil bath, at the beginning of the
decomposition the salt irreversibly transforms into a
liquid more viscous than triethanolamine.
Monomeric triethanolamine is likely to exist in the
gas phase (no experimental data are available), but in
the crystal phase it exists exclusively as dimers, where
monomer molecules are held together by six strong hyd-
rogen bonds [12]. As follows from X-ray diffraction
data and the first quantum-chemical calculation [13],
the molecule of triethanolamine has an endo
conformation, where the nitrogen lone electron pair is
directed inside the “dome.” The equilibrium structure
of the dimer is shown in Fig. 1b. The structure belongs
to the S6 point group. The arrangement of hydrogen
bonds in the dimer differs from that in the monomer:
The hydroxy groups of one of the monomers are
hydrogen-bonded to the hydroxy groups of the other,
and each hydroxy group acts both as a donor and as an
acceptor. Therefore, the monomers are held together
by six hydrogen bonds; the length of these bonds is
1.711 A, which is appreciably shorter compared to the
hydrogen bonds in the monomer. The other bonds
lengths in the dimer are close to the bonds in the
monomer: C–N bonds are slightly longer and C–C
bonds are slightly shorter. In the whole, the equilib-
rium bond lengths in the dimer are closer to the
experimental values.
We obtained an IR spectrum of triethanolamine and
tetrakis(2-hydroxyethylammonium) chloride films in
the range 4000–800 cm–1. The table lists the vibration
frequencies of these two compounds. To assign the
frequencies, we calculated harmonic vibration frequen-
cies for the triethanolamine monomer and dimer and
the [N(CH2CH2OH)4]+ cation by the B3LYP/aug-cc-
pVDZ method. As we showed previously [14, 15], the
As the molecular structure of tetrakis(2-hydroxy-
ethylammonium) chloride has never been studied, we
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 10 2014

1906
BUSLAEV et al.
(a)
θ 18.4°
(b)
Fig. 2. Equilibrium structure of the tetrakis(2-hydroxy-
ethylammonium) cation.
than the respective vibration frequencies in the tri-
ethanolamine dimer, we are safe to state that these
bonds are fairly strong.
The calculated COH bending vibration frequencies
are higher than 1500 cm–1. In view of the overesti-
mation of the strength of hydrogen bonds in the dimer
we can conclude that the experimental frequencies are
lower. However, they are likely to be obscured by
strong and broad band centered at 1456 cm–1. The
δ(CH2) frequencies, too, fall into this region.
θ 52.4°
The δ(COH) frequencies in tetrakis(2-hydroxy-
ethylammonium) chloride can be assigned to the band
at 1446 cm–1, which is absent from the spectrum of
triethanolamine. Even though certain δ(CH2) and
δ(COH) frequencies overlap each other, they are fairly
characteristic. The same relates to the wagging and
torsional vibrations of the CH2 groups. However, at
frequencies lower than 1200 cm–1, contributions of
different vibrations are mixed, which allows nothing
more than arbitrary assignments. Vibrations mostly
contributed by C–N (correspond to the IR band at
1153 cm–1), C–O (1073 cm–1), and C–C (908 and
883 cm–1) stretching can only be recognized.
Fig. 1. Equilibrium structure of triethanolamine: (a) mono-
mer and (b) dimer.
vibration frequencies of atranes calculated by this
method well fit the experimental values, except for the
C–H and, especially, O–H stretching vibration
frequencies. The reason for the latter finding is that
these frequencies are highly anharmonic, whereas the
calculation gives harmonic frequencies.
Nevertheless, the OH stretching vibration frequen-
cies in the triethanolamine dimer are close to ex-
perimental. This fact may suggest that the strength of
the hydrogen bond in the dimer is overestimated. The
calculated ν(OH) in the [N(CH2CH2OH)4]+ cation are
markedly higher, because our model does not include
cation−anion hydrogen bonds. Taking into account that
the ν(OH) frequencies in the cation are much higher
The introduction of one more ethanol moiety in
going from triethanolamine to tetrakis(2-hydroxy-
ethylammonium) chloride results in that the C–N bond
in the latter molecule much elongates and the C–C and
C–O bonds respectively shorten and elongate, though
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 10 2014

SYNTHESIS, MOLECULAR STRUCTURE, AND VIBRATIONAL SPECTRA
1907
Experimental IR spectra (ν, cm–1) and B3LYP/aug-cc-pVDZ vibration spectra (km/mol) of triethanolamine and tetrakis(2-
hydroxyethylammonium) chloride
Triethanolamine
monomerа
Tetrakis(2-hydroxyethylammonium) chloride
IR
spectrum
IR
dimera,b
calculation
assignment
spectrum
3340 s
3611 (Au), 3565 (Eu)
3405 (2332),
3303 (2684)
3098 (184),
3092 (1), 3074
(20), 3070
(114)
3263 s
3822 (81), 3818 (78), 3817 (84), 3816 ν(OH)
(102)
3201 (0), 3188 (4), 3177 (19), 3169 νas(CH2)
(1), 3129 (4), 3121 (1), 3109 (5), 3106
(7)
2950 s
3082 (Eu), 3075 (Au), 3059
(Au), 3054 (Eu)
2972 m
2882 s
3008 (Au), 3006 (Eu), 2927
(Au), 2919 (Eu)
3034 (264),
3034 (327),
2898 (545),
2887 (220)
1562 (234),
1510 (2)
2884 m
1446 m
3088 (16), 3060 (2), 3055 (29), 3053 νs(CH2)
(18), 3039 (15), 3023 (33), 3020 (27),
3018 (28)
1467 (Au), 1431 (Eu)
1262 (80), 1253 (22), 1247 (17), 1245 δ(COH)
(41)
1456 m
1510 (Au), 1503 (Eu), 1478
(Eu),
1480 (Au), 1478 (Eu)
1410 (Eu), 1394 (Au)
1495 (12), 1487 1467 m
(30), 1469 (15),
1465 (18)
1413 (8), 1397 1446 m
(13)
1382 (10), 1389
(84)
1510 (4), 1506 (1), 1503 (28), 1491 δ(CH2)
(16), 1488 (1), 1480 (26), 1469 (15),
1457 (2)
1453 (2), 1452 (14), 1446 (5), 1437 w(CH2)
(5),
1408 m
1360 m
1338 w
1282 m
1250 m
1358 (Eu), 1353 (Au)
1303 (Au), 1267 (Eu)
1422 (2), 1407 (3), 1400 (0), 1387 (3)
1310 (53), 1299
(30)
1275 (19)
1366 (17), 1361 (15)
1337 (31)
tw(CH2)
1256 (10) (Eu), 1246 (19)
(Au)
1312 m
1238 m
1264 (10)
1328 (2), 1287(4), 1272 (1)
1240 (28)
1234 (12)
1153 m
1073 s
1185 (Eu), 1103
1174 (56)
1145 (5), 1140 (2)
1126 (34)
1117 (44)
1112 (7), 1103 (23)
ν(CN)
1110 sh
1096 (Eu), 1075 (Au)
1102 (13), 1098
(419)
ν(C−O)
1040 s
972 m
1074(29)
1068(28)
1030 (50)
1068 (Au), 997 (Eu)
904 (Eu), 852 (Au)
1080 (100)
1060 (70)
909 (70)
ρ(CH2)
ν(C−C)
1035 s
908 m
1005 (93), 982 (23), 972 (6)
938 (37)
926 (32)
941 s
920 s
878 m
886 (107)
898 (16)
890 (4)
883 m
844 (Eu), 734 (Eu)
871 (200)
851 (150)
815 m
835 (3), 818 (9), 786 (6)
653(1)
ρ(CH2)
a Calculated. bGiven are only the frequencies of IR-active vibrations of the irreducible representation Au.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 10 2014

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BUSLAEV et al.
to a lesser degree. This effect reveals itself in the
predicted vibration frequencies in the range of C–N
stretching vibrations. In going from triethanolamine to
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chloride
was prepared by the procedure in [10]. The reaction
was performed in dry methanol at 115°С in a pressure
reactor for 22 h with an excess of triethanolamine.
Yield 73%, transparent hygroscopic crystals, mp 80°С
(ethanol). Found, %: C 41.52; H 11.11; N 5.97.
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