Physical and chemical properties of N-(2-hydroxyethyl)alkylamines

Article abstract of DOI:10.1134/S107042721008029X

Physical and chemical properties of N-(2-hydroxyethyl)alkylamines were studied, isotherms of a surface tension of homologous series of these compounds on a liquid-gas interface in water and hydrochloric acid were obtained. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S107042721008029X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 8, pp. 1475−1479. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Radushev, D.V. Koltashev, T.Yu. Nasrtdinova, M.G. Shcherban’, L.G. Chekanova, M.D. Plotnikova, 2010, published in
Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 8, pp. 1369−1373.
Physical and Chemical Properties
of N-(2-Hydroxyethyl)alkylamines
A. V. Radusheva, D. V. Koltasheva, T. Yu. Nasrtdinovaa, M. G. Shcherban’b,
L. G. Chekanovaa, and M. D. Plotnikovab
aInstitute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, Perm, Russia
bPerm State University, Perm, Russia
Received March 25, 2010
Abstract—Physical and chemical properties of N-(2-hydroxyethyl)alkylamines were studied, isotherms of
a surface tension of homologous series of these compounds on a liquid–gas interface in water and hydrochloric
acid were obtained.
DOI: 10.1134/S107042721008029X
It is known that N-(2-hydroxyethyl) alkylamines
(HEA) are nonionic surfactants [1]; N-(2-hydroxyethyl)
alkylamines with radicals C5N11–C8H17 were suggested
as precipitants for waste water treatment from ions of
Cu(II) [2]. The presence of amine and hydroxyethyl
groups in these compounds opens up prospects for their
use as complexing agents, including surfactant properties.
However, information on their physical and chemical
properties is necessary for practical application of HEA.
In the literature there are only fragmentary data on the
properties of some of the lower representatives of this
series [2].
hexane and 2–3 fold recrystallization from a hexane–ethyl
acetate mixture (1 : 1). In the case of the reagent with R =
C8Н17 cleaning was performed by a vacuum distillation.
Identity and purity of compounds were confirmed by
1
IR and H NMR spectroscopy and elemental analysis.
An amount of the main substance in the samples was not
less than 96%, it was determined by the potentiometric
titration in an I160M ionomer equipped with glass and
silver chloride electrodes. We dissolved a weighted por-
tion of the sample (0.1 g) in 20 ml of ethanol, then we
added 16 ml of distilled water and 4 ml of 1 M KCl so-
lution and titrated with 0.1 M aqueous solution of HC1.
Calculation of HEA content (%) was conducted by the
following formula
The aim of this work was to study the physical and
chemical properties in a HEA series to assess the possi-
bility of using them in the separation and concentration
of metals or as a surfactant.
(2)
EXPERIMENTAL
where VHCl is a volume of hydrochloric solution treated
for titrating (ml); NHCl, a concentration of the working
solution of HCl (M); М, molecular weight of the appro-
priate HEA.
N-(2-Hydroxyethyl) alkylamines of RNHCH2CH2OH
formula, where R = C8Н17–C16H33 was prepared by a re-
action of monoethanolamine with primary chloroalkanes
according to technique described in [2]:
Computation of рKа values of the compounds with
the aid of potentiometric measurements was conducted
by the following equation [3]
CnH2n+1Cl + NH2СН2СН2ОН
' CnH2n+1NHСН2СН2ОН + НСl.
(1)
(3)
The products were purified gradually by washing with
1475

1476
RADUSHEV et al.
where α is neutralization degree of HEA (a fraction of
a unit) сL is HEA concentration in the weighted sample
(M), [Н+] and [OH–] are concentration of the ions in the
computation point in a titration curve (M).
with heating the plate to 70°C. The surface tension at the
interface of aqueous solution of HEA–air, HEA solution
in 0.1 M HCl–air was measured by stalagmometr [5].
The critical micelle concentration (CMC) was determined
graphically by the points of inflection on the plot of sur-
face tension dependence on the concentration of reagents.
Solubility was determined by gravimetric method
[4], thermal stability was studied on a Q-1500D MOM
company derivatograph (Hungary) in air at a temperature
of 20–600°C at a heating rate of 10 deg min–1. 1H NMR
spectra were recorded on a MERCURY plus 300 spec-
trometer in CDCl3, the IR spectra, by Fourier IFS 66
spectrometer (Bruker, Germany): suspension in vaseline
oil, glass of KBr, a resolution of 1 cm–1, 100 scans. El-
emental analysis was performed on a CHNS-932 analyzer
(LECO Co., USA).
The test reagents (Table 1) were white crystalline
substance (except reagent with R = C8H17, which was
a liquid). NMR spectra of compounds obtained are pre-
sented in Table. 2. For compounds III and IV (Table 2)
values of proton chemical shifts of OH- and NH-groups
coincide. The IR spectra of these reagents have absorp-
tion bands of medium intensity in the regions of 3290
and 3280 cm–1 [ν(NH)] and 3150 and 3120 cm–1 [ν(OH)],
respectively.
To study the stability to acid hydrolysis the weighted
samples containing 5 × 10–2 mol of reagent were thermo-
statically controlled to within 1 day in 0.1 M HCl solution
at 20 and 60°C. Monitoring the hydrolysis was carried
out at regular time intervals by TLC on Silufol plated in
a chloroform–methanol system (1 : 2), the developing
was performed by a 3% solution of chloranil in toluene
Data on the solubility of reagents (Table 1) demon-
strate that the compounds are of poor solublility in water,
of moderate one in aqueous solutions of HCl, and of
good solubility in ethanol; their use is preferably in the
form of hydrochloride salts. With increasing length of
hydrocarbon radical the solubility of reagents markedly
Table 1. Melting points and solubility of compounds RNHСН2CН2ОН at Т = 20°C
Solibility, M
0.1 M HCl
1.2 × 10–1
1.3 × 10–1
1.1 × 10–1
1.1 × 10–3
9.1 × 10–4
Compd. no.
R
mp, °C
water
EtOH
>0.9
>0.8
>0.7
>0.4
>0.1
I
C8H17
125–126/4 Hg mma
28–29
3.0 × 10–3
2.0 × 10–3
3.9 × 10–4
3.9 × 10–4
2.8 × 10–4
II
C10H21
C12H25
C14H29
C16H33
III
44–45
IV
54–55
V
58–59
* bp is noted here.
Table 2. 1HNMR spectroscopy data of compounds RNHСН2CН2ОН
δ,a ppm
Compd.
R
RСН2N
NH
(s)
RСН2СН2N
no.
ОН(s)
СН2ОН(t) СН2СН2ОН(t)
ССН2С(m) СН3(t)
(t)
(m)
I
С8Н17
3.10
3.16
2.34
2.28
3.18
3.64
3.65
3.64
3.63
3.62
2.73
2.77
2.76
2.76
2.76
2.60
2.61
2.63
2.60
2.60
1.95
2.00
2.39
2.28
1.78
1.48
1.49
1.48
1.48
1.47
1.26
1.25
1.25
1.25
1.25
0.87
0.87
0.87
0.87
0.87
II
С10Н21
С12Н25
С14Н29
С16Н33
III
IV
V
a (s) singlet, (t) triplet, (m) multiplet.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010

PHYSICAL AND CHEMICAL PROPERTIES OF N-(2-HYDROXYETHYL)ALKYLAMINES
1477
reduced (except reagent II in 0.1 M HCl, where there is
a maximum solubility). The choice of these solvents was
portion of the curve reflects a gradual filling of the surface
layer by the surfactant molecules thereby the adsorption
made from practical considerations: application of HEA attains the limiting value, the further input of the surfac-
to the flotation of metals.
tant leads to the micelle formation in a bulk of the solution
and does not effect on the surface tension of the solution.
The further growth in the surfactant concentration causes
a transition from spherical micelles formed in the solu-
tions at the small surfactant concentrations to asymmetric
ones, aspheric, that affects the state of the surface layer
[7]. These changes result in the shape of the following
portion of the isotherm where a further gradual decrease
in the surface tension occurs.
Based on data of the thermal analysis we established
that up to 140°С the compounds are stable. In the tem-
perature range 140–275°С there is thermal decomposi-
tion of all the samples accompanied by a considerable
loss of weight.
Like the aliphatic amines, the compounds under study
have the basic properties due to an capability of lone pair
of electrons of the nitrogen atom to attach a proton. Ba-
sicity of HEA can be characterized by the values of acid
dissociation constants Ka of conjugated acids:
The results are evidence that HEA series belongs to
a class of the strong surfactant since minimal values of
the surface tension σmin of compounds with R = C8H17,
C10H21, C12H25 are 25–45 mJ m–2 in water, of compounds
with R = C8H17, C10H21, C12H25, C14H29 in 0.1 M HCl,
30–35 mJ m–2 (Table 3). The slight decrease in the surface
[R–NH2–CH2CH2OH]+
Ka
→ R–NH–CH2CH2OH + H+.
(4)
tension by compounds with R = C14H29 in water (σmin
=
63 mJ m–2) and with R=C16H33 in water and in 0.1 M HCl
Results of the computations of рKa of the conjugated
acids RNHСН2CН2ОН series, calculated according to
data of the potentiometric, show that the constant values
are practically independent of the length of the HEA
radical; in comparison with monoethanolamine [6] the
basicity of the compounds under study changes slightly.
(a)
Chemical stability of HEA is determined by their
resistance to hydrolysis, which will most likely be oc-
cur with the formation of the primary amine (A) and
ethylene glycol. The chemical stability was assessed
by thin layer chromatography (TLC) on the example of
N-(2-hydroxyethyl) dodecylamine. The most suitable was
chloroform–methanol solvent system (1 : 2), for which
values of the relative speed of movement Rf of the reagent
under study and a hydrolysis product (dodecylamine)
were 0.45 and 0.60, respectively. Found that the reagent is
chemically stable to within a 1 day in 0.1 M HCl solution
at 20°C. At 60°C after 45 min in the chromatogram were
revealed two spots corresponding to the initial reagents
and dodecylamine; after 1 h incubation reagent was
completely hydrolyzed: only one spot of dodecylamine
was revealed.
(b)
Figure 1 shows he isotherms of the surface tension
of the solutions of HEA with R=C8H17 (curve 1), C12H25
(curve 2), and C14H29 (curve 3). The isotherms of the
reagents with R = C10H21, C16H33 were analogous. In
the region of the HEA small concentrations a value of σ
decreases sharply and then a decrease in the surface ten-
sion slows upon the concentration growth. A descending
Fig. 1. The isotherms of the surface tension σ (mJ m–2) of
compounds RNHCH2CH2OH (a) in water and (b) in 0.1 M
HCl. (с) Concentration, M. R: (1) C8H17, (2) C12H25, (3) C14H29.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010

1478
RADUSHEV et al.
Table 3. Minimal value of the surface tension in water and in 0.1 M HCl compounds RNHСН2CН2ОН, critical micelle
centration (CMC) and surface activity G at Т = 20°C
σ
min, mJ m–2 (сreagent, M)
ККМ, M
0.1 M HCl
G, kg m3 s–2 mol–1
water 0.1 M HCl
Compd. no.
R
water
0.1 M HCl
35(28.8)
water
1
40
I
C8H17
C10H21
C12H25
C14H29
C16H33
2
0.033
0.072
0.084
0.400
0.417
0.020
0.008
0.011
0.088
0.125
(2.65)
24
II
28(24.8)
32(6.97)
36(1.12)
0.68
0.32
5.5
4
(1.58)
III
IV
V
46(0.44)
63
0.025
0.024
0.43
0.032
(0.20)
70
(0.175)
63(0.14)
(σmin 63 and 70 mJ m–2, respectively) is influenced by
their small solubility in water (Table 1). With increasing
the length of the radical increases the ability of micelle
reagents. The most promising surfactant of this series
based on a complex of the physical and chemical proper-
ties is N-(2-hydroxyethyl)dodecylamine.
on the linear portion of the isotherm of surface tension
for all the studied homologues and meets the condition
c
reagent > 0. Dependence ln cΔσ–n is shown in Fig. 2.
The calculated value of ΔW was in the water and in
0.1 m HCl 1.28 and 0.645 kJ mol–1, respectively, and
that is below the theoretical value (~ 2.7 kJ mol–1) for the
aqueous medium [8]. Such a deviation may be due to the
large number of carbon atoms in the radical (n = 8–16,
whereas ΔWtheor corresponds to n = 3–6) and to the pres-
ence of two heteroatoms causing an increase in the lateral
cohesive interaction of surface molecules of HEA. For
the same reason too low values ofΔW compared with the
theoretical ones were observed, for example, for a series
of 1,1-dimethyl-1-alkylhydrazinium chlorides [9].
In the homologous series of surfactant the surface ac-
tivity is largely dependent on the number of carbon atoms
in the chain and increases with a growth of the length of
the hydrocarbon radical [7]. The surface activity G can
be determined by the equation [7]
where δ is an adsorption layer thickness, m; W0, an ad-
sorption work of polar groups, J mol–1; n, a number of
methylene group; ∆W, the contribution of one methylene
link in the adsorption work (J mol–1), R, universal gas
constant, J mol–1 K–1; T, temperature, K.
Computed values are listed in Table 3.
From equation (5) implies that for the homologous
series a dependence in the coordinates ln cΔσ–n should
be linear with slope tan α = ΔWR–1T–1, where cΔσ, the
surfactant concentration causing a reduction in the surface
tension on the magnitude ofΔσ;ΔW, a growth rate of the
adsorption potential: the contribution of a CH2 link to the
work of adsorption. The obtained isotherms of the surface
tension allow calculation of this characteristic for the ho-
mologous series of HEA. The calculation was performed
at σx = 70 mJ m–2. The value of the surface tension lies
Fig. 2. Effect of the radical length in the surface activity of
compounds RNHCH2CH2OH in (1) water and (2) in 0.1 M HCl.
(cΔσ) the reagent concentration, M, (n) a number of the methy-
lene groups in alkyl radical.
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PHYSICAL AND CHEMICAL PROPERTIES OF N-(2-HYDROXYETHYL)ALKYLAMINES
1479
CONCLUSIONS
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ACKNOWLEDGEMENT
This work was supported by RFBR (grant no. 10-03-
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010