Hydrolysis of 1,2-disubstituted imidazolines in aqueous media

Article abstract of DOI:10.1023/B:RUCB.0000037846.18796.e8

The kinetics of hydrolysis of 1,2-disubstituted imidazolines in aqueous media was studied (pH 2.0 - 12.5, T = 25 - 90°C) by UV spectroscopy. The hydrolysis products were identified. The introduction of a branched substituent into position 2 of the imidazoline ring increases the hydrolytic stability of the compounds. The effect of the pH on the hydrolysis rate of imidazolines is discussed.

Full text of DOI:10.1023/B:RUCB.0000037846.18796.e8

Russian Chemical Bulletin, International Edition, Vol. 53, No. 4, pp. 803—807, April, 2004
803
Hydrolysis of 1,2ꢀdisubstituted imidazolines in aqueous media
b
b
a
S. O. Bondareva,a V. V. Lisitskii, N. I. Yakovtseva, and Yu. I. Murinov
ꢀ
aInstitute of Organic Chemistry, Ufa Research Center, Russian Academy of Sciences,
71 prosp. Oktyabrya, 450054 Ufa, Russian Federation.
Fax: +7 (347 2) 35 6066. Eꢀmail: murinov@anrb.ru
bBashkir State University,
32 ul. Frunze, 450074 Ufa, Russian Federation
The kinetics of hydrolysis of 1,2ꢀdisubstituted imidazolines in aqueous media was studied
(рН 2.0—12.5, T = 25—90 °С) by UV spectroscopy. The hydrolysis products were identified
The introduction of a branched substituent into position 2 of the imidazoline ring increases the
hydrolytic stability of the compounds. The effect of the pH on the hydrolysis rate of imidazolines
is discussed.
Key words: substituted imidazolines, hydrolysis rate constants, hydrolysis products, protoꢀ
nation of imidazolines.
The use of 1,2ꢀdisubstituted imidazolines (DI) for the
preparation of cationꢀactive and ampholytic surfactants
was started more than 50 years ago. Their derivatives are
used today as corrosion inhibitors in processes of petroꢀ
leum production, transportation, and refining. Various
detergents, antistatics for polymeric materials processing,
hardeners of polymeric resins, accelerators of vulcanizaꢀ
tion, and textileꢀauxiliary substances of manyꢀsided deꢀ
sign were created on the basis of DI.1 A possibility and
expediency of industrial use of DI depend, to a great
extent, on their hydrolytic stability. Amphoteric DIꢀbased
surfactants were synthesized in aqueousꢀbasic media at
40—98 °С.2 To intensify petroleum production, highly
mineralized water (sometimes sea water) is pumped into a
bed or acid treatment of aquifers is used.3 Similar factors
can result in imidazoline hydrolysis.
that the introduction of a branched substituent into the
αꢀposition to the reaction center can hinder the addition
of the hydroxide ion and, hence, inhibits imidazoline
hydrolysis.
The purpose of this work is to study the kinetics of
hydrolysis of some 1,2ꢀdisubstituted imidazolines in aqueꢀ
ous media in a wide pH interval and to determine the
hydrolytic stability of imidazolines with an αꢀbranched
substituent in position 2 of the ring.
Experimental
All compounds were synthesized by the condensation of
anhydrous diethylenetriamine (DETA) or triethylenetetraamine
with linear (acetic and octanoic) and αꢀbranched (2ꢀethylꢀ
hexanoic) carboxylic acids at a molar ratio of 1 : 0.9 in a nitroꢀ
gen atmosphere at 200—300 °С.6
Imidazoline samples (Tables 1 and 2) containing at least
95% of the main substance were used. Previously described7,8
imidazolines 1 and 2 were synthesized as model substances. To
identify hydrolysis products, we also synthesized Nꢀ(5ꢀaminoꢀ
3ꢀazapentyl)ꢀ2ꢀethylhexaneamide (3а), which is the most probꢀ
able product of hydrolysis of compound 3. Purity of compounds
was monitored by GLC 9 on a Chromꢀ5 instrument (He, colꢀ
umn 1.2 m×3 mm with 15% SEꢀ30 on Chromaton NꢀAW).
Electronic spectra were recorded on Specord UV—Vis
The usual2,4,5 scheme of hydrolysis of substituted
imidazolines in aqueousꢀbasic media (Scheme 1) suggests
Scheme 1
and Specord Mꢀ40 spectrophotometers in
a region of
50500—28000 cm–1 (in EtOH). IR spectra were recorded on a
Specord Mꢀ80 spectrophotometer (in film). 13С NMR spectra
were measured on a Bruker AMꢀ300 spectrometer (CDCl3,
Me4Si). Potentiometric studies were carried out on an ORꢀ211/1
pHꢀmeter with a combined glass electrode in water (1 М КCl)
using a known procedure.10
The content of imidazolines in a solution during hydrolysis
was determined by UV spectroscopy from the intense absorption
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 767—771, April, 2004.
1066ꢀ5285/04/5304ꢀ0803 © 2004 Plenum Publishing Corporation

804
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 4, April, 2004
Bondareva et al.
Table 1. Physicochemical characteristics of the synthesized compounds
Compound
Structural
formula
Yield
(%)
B.p.
/°С
Found
Calculated
Molecular
formula
(%)
(р/Torr)
С
Н
N
Ntitr
1ꢀ(2ꢀAminoethyl)ꢀ2ꢀmethylꢀ
4,5ꢀdihydroimidazole (1)
85
88
81
110—112
(2)
56.50
56.66
10.65
10.30
—
—
21.05
22.03
C6H13N3
C12H25N3
C12H25N3
1ꢀ(2ꢀAminoethyl)ꢀ2ꢀheptylꢀ
4,5ꢀdihydroimidazole (2)
133—135
(1—2)
67.02
68.20
11.87
11.92
12.59
13.25
1ꢀ(2ꢀAminoethyl)ꢀ2ꢀ(1ꢀethylꢀ
pentyl)ꢀ4,5ꢀdihydroꢀ
imidazole (3)
140—142
(2—3)
68.37
68.20
11.90
11.92
18.80
19.88
13.20
13.25
Nꢀ(5ꢀAminoꢀ3ꢀazapentyl)ꢀ
2ꢀethylhexaneamide (3a)
92
77
190—192
(2—3)
63.21
62.84
12.08
11.86
18.41
18.32
12.30
12.21
C12H27N3O
C14H30N4
1ꢀ(5ꢀAminoꢀ3ꢀazapentyl)ꢀ
2ꢀ(1ꢀethylpentyl)ꢀ
182—185
(2)
65.08
66.09
11.93
11.88
20.00
22.02
15.41
16.52
4,5ꢀdihydroimidazole (4)
1ꢀ(5ꢀEthylꢀ4ꢀoxoꢀ3ꢀazanonyl)ꢀ
2ꢀ(1ꢀethylpentyl)ꢀ4,5ꢀ
55
210—213
(1—2)
71.76
71.17
12.08
11.65
11.93
12.45
4.39
4.15
C20H39N3O
dihydroimidazole (5)
π→π*ꢀband at 230—235 nm, which corresponded to the transiꢀ
tion of the С=N bond in the heterocycle.8 Samples were hydroꢀ
lyzed in a cell, whose temperature was maintained constant, at a
constant stirring velocity. The conversion of imidazolines was at
least 60% in an interval of рН 7.0—9.0 and at least 90% at
рН > 9.0 (hydrolysis did not virtually occur in acidic media).
The pH value was monitored by an ORꢀ211/1 pHꢀmeter with a
combined glass electrode, and a needed value was established by
the addition of 0.1 М HCl or 0.1 М NaOH.
The preliminary experiment established that at the molar
ratio imidazoline : water 1 : 50—1 : 150 the hydrolysis rate
constants for DI were virtually unchanged. Therefore, experiꢀ
ments were carried out at the molar ratio imidazoline : water
1 : 120, the concentrations of imidazolines 3, 4, and 5 beꢀ
ing ∼0.4, ∼0.3, and ∼0.25 mol L–1, respectively.
Results and Discussion
Table 2. Spectral characteristics of the synthesized compounds
Identification of hydrolysis products. Hydrolysis prodꢀ
ucts (HP) of imidazolines isolated from working solutions
were studied by GLC, IR spectroscopy, and 13С NMR
spectroscopy. The chromatogram of the HP of imidazoline
3 exhibits a small peak of nonꢀhydrolyzed imidazoline,
which is eluted first, followed by two rather intense peaks
with very close retention times (Fig. 1). The retention
times of these peaks coincide with the elution time of
compound 3а. Analysis of the chromatogram shows that
the HP of imidazolime 3 also contain minor amounts of
acylated imidazoline 5 and bisacylated DETA. It is likely
that imidazoline 5 is primarily present as an amine adꢀ
mixture in the hydrolyzed samples of imidazoline 3 and is
partially hydrolyzed during experiment to form bisꢀ
acylated DETA.
Comꢀ
pound λ/nm (logε)
UV,
IR,
ν/cm–1
13С NMR
(δ)
1
202 (3.41),
231 (3.75)
1600 (ν(C=N));
1016 (ν(C—N) ring);
940 (δ(Me))
164.21 (s,
>С=N)
2
205 (3.30),
1610 (ν(C=N));
168.50 (s,
>С=N)
170.70 (s,
>С=N)
231.5 (3.77) 998 (ν(C—N) ring)
202 (3.20), 1610 (C=N);
232.5 (3.78) 998 (ν(C—N) ring)
3
3a
4
204 (3.60)
1644 (ν(C=O));
1552 (δ(NH))
176.05 (s,
NHC=O)
170.57 (s)
204 (3.28),
236 (3.79)
201 (3.67),
234 (3.83)
1604 (ν(C=N));
996 (ν(C—N) ring)
1644 (ν(C=O));
1605 (ν(C=N));
1552 (δ(NH));
5
170.43 (s,
>С=N);
176.11 (s,
NHC=O)
The data of IR spectroscopy (Table 3) indicate the
amide structure of the HP. The IR spectra of the HP are
virtually identical with the IR spectrum of individual amide
1000 (ν(C—N) ring)

Hydrolysis of 1,2ꢀdisubstituted imidazolines
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 4, April, 2004
805
2
Table 4. 13С NMR spectra of the hydrolysis products of imidꢀ
azolines
Atom
δ
C
HPꢀ2
HPꢀ3
3а
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
37.48 (w), 37.65
39.62
42.05
52.24
173.45 (w), 173.64
49.13 (w), 49.30
40.33 (w), 40.55
42.01
38.71
41.32
48.57
51.50
176.05
49.34
44.12
52.38 (w), 52.54
177.41, 177.60
50.03 (w), 50.22
1
data.11 For example, a scheme of alkaline hydrolysis of
1,2ꢀdisubstituted imidazolines was proposed (Scheme 2).
Reaction a was proved to be the main process, whereas
the product of reaction b is formed only in insignificant
amounts.
3
4
0
t
Scheme 2
Fig. 1. Chromatogram of the hydrolysis products of imidazoꢀ
line 3: nonꢀhydrolyzed imidazoline 3 (1), monoacylated DETA
(3а) (2), monoacylated imidazoline 5 (3), and bisacylated
DETA (4); vertical arrow corresponds to the moment of sample
injection.
3а but differ from the latter by a noticeable broadening of
the bands.
The 13С NMR spectra confirm the amide structure of
the HP (Table 4), and the downfield signal of the
sp2ꢀhybridized C atom of the amide group (С(5)) is the
most characteristic. The most part of signals in the spectra
of the HP are duplicated by less intense signals, which
differ from the main signals by ∼0.2 ppm. It is most likely
that some isomeric amide is formed as an admixture along
with the main product, which agrees with the published
Thus, amide 3a is the HP of imidazoline 3. Solutions
of amide 3а in an H2O—PriOH mixture were stored for
1—3 days at 85 5 °С; however, they did not show DETA
and 2ꢀethylhexanoic acid. Evidently, the hydrolysis of
amides with an αꢀbranched substituent requires more
"drastic" conditions or a longer reaction time.
Kinetics of hydrolysis of imidazolines. The consumpꢀ
tion of imidazolines during hydrolysis is described by an
equation of the pseudoꢀfirst order: the effective hydrolysis
constants of DI with linear (1, 2) and αꢀbranched alkyl
substituents in position 2 of the imidazoline ring (3—5)
are given in Table 5. The published data for their closest
analogs, viz., 1ꢀ(2ꢀhydroxyethyl)ꢀ2ꢀnonylimidazoline (6)
and 1ꢀ(2ꢀaminoethyl)ꢀ2ꢀdecylimidazoline (7), are given
for comparison.
As expected, the introduction of a branched substituꢀ
ent into the αꢀposition to the reaction center substantially
inhibits the hydrolysis rate. For example, at 90 °С and
рН 12.4, sample 2 is completely hydrolyzed already within
12—15 min, whereas its isomer (sample 3) is hydrolyzed
only within 5—6 h, i.e., the hydrolysis rate slowed down
Table 3. Characteristic frequencies of vibrations of molecules of
the hydrolysis products of imidazolines in the IR region
Type of vibrations
ν/cm–1
HPꢀ1
HPꢀ2
HPꢀ3
3а
ν(NH2)
3296
3300,
3296,
3288
3190 sh
3080 w
3190 sh
3060 w
Overtone ν(С=О)
ν(C=O) (I amide
band)
δ(NH) (II amide
band)
3100 w
3060
1640
1660 sh, 1660 sh, 1638 br
1648
1568
1640
1560
1552 br
740 br
1560
740
δ(NH)
725 br
728 br
outꢀofꢀplane

806
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 4, April, 2004
Bondareva et al.
Table 5. Effective hydrolysis constants (keff) of imidazolines in
an aqueous medium at different temperatures (25—90 °С),
рН 12.4
Table 6. Activation parameters of hydrolysis
of imidazolines at pH ≈ 12
Compound
log(A/s–1
)
EА/kJ mol–1
Compound
keff•105/s–1
2a,b
3b
4.1
4.1
4.4
2.6
8
44.6
53.8
54.6
39.2
67
25 °С
50 °С
75 °С
90 °С
5b
1a
2a
21.8 2.6
20.0 2.3
—
—
—
—
—
500 85
6c,d
7a,c,d
3a
0.37 0.02 2.8 0.1
7.8 0.6 20.8 1.4
4a
—
—
—
15 1.5
20 1.4
37
a The parameters were estimated from two valꢀ
ues of effective hydrolysis constants measured
at two temperatures.
5a,b
0.67 0.02 7.2 0.1
2
b This work.
(6)c
(7)d
—
∼31
—
—
—
c The values were calculated from the experiꢀ
mental data presented.
d See Refs. 4 and 11.
∼56e
∼290
—
stable during at least 6 months. However, an almost 100%
conversion is observed13 on heating 1,2ꢀdiꢀ and 2ꢀmonoꢀ
substituted imidazolines for 6 h at 140 °С and рН ≈ 0—1.
Therefore, it can be assumed that comparatively drastic
conditions are needed to decompose the imidazoline
structure in acidic media.
a This work.
b In an H2O—PriOH mixture.
c See Ref. 4.
d See Ref. 11.
e T = 30 °C.
The influence of the pH on the hydrolysis of DI was
studied for compound 3 in an interval of рН 2.0—12.7 at
70 and 90 °С. The plot of logk vs. pH is presented in
Fig. 3, a. Two rectilinear regions with the inflection point
at рН ≈ 10 are well seen, and the distribution curves for
the protonated forms of compound 3 in water are given
for comparison (see Fig. 3, b). They were calculated from
the previously6 determined stepwise protonation constants
of imidazoline 3. The inflection point in the plot (see
Fig. 3, a) approximately corresponds to the maximum
content of imidazoline protonated at the primary amino
group. With an increase in the pH, the equilibrium shifts
toward the formation of the nonꢀprotonated form of DI;
the tangent slope close to 1 indicates the first order of the
reaction with respect to the hydroxide ion.14 Hydrolysis is
not virtually observed at рН < 6. However, the content of
DI protonated at the tertiary N atom in the imidazoline
ring is maximum at these pH values. It is most likely that
the positive charge on the N atom (structure B) prevents
by at least 25 times. Comparison of the experimental hyꢀ
drolysis rate constants (k) with the published data (taking
into account minor differences in the temperature, рН,
and concentrations) also gives a difference of 10—50 times.
The activation parameters of hydrolysis of 1,2ꢀdisubꢀ
stituted imidazolines with a branched substituent in posiꢀ
tion 2 of the imidazoline ring (Table 6) were determined
from the temperature dependence of lnk (Fig. 2). The
published data of imidazolines with linear substituents are
given in Table 6 for comparison.
In our opinion, the hydrolysis of DI in acidic media is
studied in less detail: the commonly accepted scheme for
acid hydrolysis is absent, and published data are poorly
generalized. For example, it has been reported5,12 that in
acidic media (рН ≈ 1—2) solutions of imidazolines are
ln(k/s–1
)
–6
–8
2
5
3
–10
–12
0.0028
0.0030
0.0032
T
–1/K–1
Fig. 2. Temperature dependence of the hydrolysis rate conꢀ
stant (k) for the hydrolysis of 1,2ꢀdisubstituted imidazolines
with αꢀbranched (3, 5) and linear (2) alkyl substituents.

Hydrolysis of 1,2ꢀdisubstituted imidazolines
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 4, April, 2004
807
8
10
pH
likely, causes the hydrolysis of imidazolines in acidic
media.
References
a
1. P. S. Belov, V. I. Frolov, and B. E. Chistyakov,
Novye poverkhnostnoꢀaktivnye veshchestva na osnove
zameshchennykh imidazolinov [New Surfactants Based on Subꢀ
stituted Imidazolines], TsNIITEneftekhim, Moscow, 1975,
54 pp. (in Russian).
2. B. S. Kolomiets, V. K. German, and V. V. Suchkov, Zh. Prikl.
Khim., 1978, 2758 [J. Appl. Chem. USSR, 1978 (Engl.
Transl.)].
–4
–6
log(k/s–1
)
3. V. A. Antipov and V. I. Levashova, Neftekhimiya, 2002, 6,
475 [Petroleum Chemistry, 2002, 6 (Engl. Transl.)].
4. B. S. Kolomiets, V. K. German, and V. V. Suchkov, Zh. Prikl.
Khim., 1978, 1141 [J. Appl. Chem. USSR, 1978 (Engl.
Transl.)].
5. V. P. Kasperchik, G. I. Sergeev, and V. S. Soldatov, Dokl.
Akad. Nauk BSSR [Rev. Acad. Sci. Belorussian Acad. Sci.],
1988, 7, 621 (in Russian).
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Akad. Nauk, Ser. Khim., 2000, 2041 [Russ. Chem. Bull., Int.
Ed., 2000, 49, 2007].
7. V. V. Krut´, Author´s Abstract, Ph. D. (Chem.) Thesis, Mosꢀ
cow, 1967, 23 pp. (in Russian).
b
α
H2L2+
HL+
1.0
0.8
0.6
0.4
0.2
H3L3+
L
8. P. A. Perov, V. V. Krut´, G. A. Tember, and N. T.
Gerasimova, Zh. Prikl. Spektrosk., 1980, 309 [J. Appl. Spectr.,
1980, No. 2 (Engl. Transl.)].
9. G. I. Batukova, V. D. Davydov, and N. S. Rodimushkina,
Zh. Anal. Khim., 1977, 1462 [J. Anal. Chem. USSR, 1977,
No. 7 (Engl. Transl.)].
10. F. R. Hartley, C. Burgess, and R. M. Alcock, Solution Equiꢀ
libria, Ellis Horwood, New York—Chichester—Brisbane—
Toronto, 1980.
11. A. Savignac, T. Kabbage, P. Dupin, and M. Calmon,
J. Heterocycl. Chem., 1978, 15, 897.
12. R. B. Martin, A. Parcell, J. Am. Chem. Soc., 1961, 83, 4834.
13. B. S. Kolomiets, V. K. German, and V. V. Suchkov, Zh. Prikl.
Khim., 1978, 2119 [J. Appl. Chem. USSR, 1978 (Engl.
Transl.)].
0
2
4
6
8
10
pH
Fig. 3. Effect of the рН on the hydrolysis rate of imidazoline 3 at
90 °С (a) and the distribution of the protonated forms of comꢀ
pound 3 in the 3—HCl—H2O system for different рН at
25 °С (b); α is the molar fraction.
hydrolysis via Scheme 1, because the partially positive
charge on the C atom is not formed in this case (A).
No protonation of the imidazoline molecule at the
sp2ꢀhybridized N atom (structure С) was observed under
the comparatively mild conditions chosen. In this case,
the presence of two like charges in the ring can result in
the decomposition of the imidazoline structure and, most
14. N. M. Emanuel´ and D. G. Knorre, Kurs khimicheskoi
kinetiki [The Course of Chemical Kinetics], Vysshaya Shkola,
Moscow, 1984, 463 pp. (in Russian).
Received July 30, 2003;
in revised form December 9, 2003