Oligomerization of cyclic imines N-carboxamides by the action of anion type catalyst

Article abstract of DOI:10.1134/S1070363211010130

Using methods of nuclear magnetic resonance, gel-permeation chromatography, and differential-scanning calorimetry, we showed that N-carboxamides were capable of polymerization. The polymerization mechanism of N-carboxamides in the presence of e-caprolactam sodium salt was suggested.

Full text of DOI:10.1134/S1070363211010130

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 1, pp. 91–95. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © F.M. Filippova, R.R. Spiridonova, A.M. Kochnev, Ya.D. Samuilov, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81,
No. 1, pp. 93–98.
Oligomerization of Cyclic Imines N-Carboxamides
by the Action of Anion Type Catalyst
F. M. Filippova, R. R. Spiridonova, A. M. Kochnev, and Ya. D. Samuilov
Kazan State Technological University, ul. K. Marksa 68, Kazan, Tatarstan, 420015 Russia
e-mail: faridah@rambler.ru
Received March 1, 2010
Abstract―Using methods of nuclear magnetic resonance, gel-permeation chromatography, and differential-
scanning calorimetry, we showed that N-carboxamides were capable of polymerization. The polymerization
mechanism of N-carboxamides in the presence of ε-caprolactam sodium salt was suggested.
DOI: 10.1134/S1070363211010130
Recently the interest of scientists grew to the
chemistry of cyclic imines. Consequently the spectrum
of their application was extended. These compounds
can be used in pharmacology as antibacterial drug
components [1]. They can be used also as polyvinyl
chloride plasticizers, catalysts in polyurethane syn-
thesis, epoxy resin hardeners, antioxidants for rubber,
etc. [2–5].
Our earlier studies showed that cyclic saturated
imines are incapable of entering into the poly-
merization under the conditions of anionic initiation
[6]. Therefore it is of interest to estimate the influence
of different substituents at the nitrogen atom of the
cyclic imine carboxamides on the ability to poly-
merization via ring opening.
N-(cyclohexylazepane)-1-carboxamide
phenylazepane-1-carboxamide Ib, N-(4-chlorophenyl)
azepane-1-carboxamide Ic, N,N'-(4-methyl-1,3-
Ia,
N-
Cyclic saturated imines (pyrrolidine, piperidine,
hexamethyleneimine and others) and their derivatives
can be considered as potential monomers, whose poly-
merization may lead to new high-molecular com-
pounds possessing unique properties inherent to this
class. However, there are no data in the literature on their
application as monomers for the synthesis of polymers.
phenylene)-diazepane-1-carboxamide IIa, and also
N,N'-hexane-1,6-diylazepane-1-carboxamide IIb ob-
tained by the reaction of hexamethylene imine with
different isocyanates were selected as cyclic imine N-
carboxamides for the investigation.
R
N
C
NH
R
O
C
N
NH +
O
Iа−Ic
(а),
(c).
(b),
R =
Cl
N
2
R' N
C
O
NH R' NH C
O
C
N
N
C
O
+
NH
O
IIа, IIb
CH3
(b).
(a),
R =
CH2
6
91

92
FILIPPOVA et al.
Probable mechanism of cyclic polymerization of
Reactions with the participation of selected cyclic
imine N-carboxamides in the presence of a catalytic
amount of compound III at 180–190°C afford the
products of light beige color, whose yield is given in
Table 1. It follows from the data in Table 1 that in all
cases when N-carboxamides were used the yields of
the obtained compounds extracted into acetone were
sufficiently high.
the imine N-carboxamides under the action of ε-capro-
lactam sodium salt III can be represented as follows:
(1) Initiation reaction. At the nucleophilic attack of
the lactam anion on the monomer amide carbon atom
an anion is formed, which is stabilized through the
cycle opening to give the N-anion, which plays the role
of an active center:
The study of molecular-mass characteristics by the
gel-permeation chromatography method showed that at
least four monomer molecules were added in the
reaction. The reaction products of cyclic imines N-
carboxamides Ia and IIb, which contain no aromatic
rings in their chemical structure, are characterized by
the largest values of Mw. To explain the observed
results we carried out a comparative analysis of the
first LUMOs of the studied compounds (Fig. 1). It was
shown that the LUMO of N-carboxamides containing
aromatic substituents in their structure have no
occupancy on the carbon atoms of the heterocycle
fragments СН2–N (Figs. 1b, 1d). The occupancy on
these atoms appears only in the third (in the case of Ib)
and the second (IIa) LUMOs (Figs. 2, 3). This
predetermines the greater probability of the
nucleophilic attack on the heterocycle carbon atom,
accompanied by the breaking of C–N bond, in the case
of aliphatic N-carboxamides in comparison with
aromatic analogs.
CH2
(CH2)n
CH2
(CH2)5
+
NH R
N
C
O
Na
N
O
C
C
N
O
(CH2)5
Na
C
(CH2)n+2
N
NH
R
O
(2) Chain growth reaction. The obtained N-anion
attacks the monomer molecule at the amide carbon
atom of the ring, opens the N-carboxamide ring, and
adds to it to form in this case a trimer, which again
carries an anion. The trimer anion again attacks N-
carboxamide molecule and thus the chain growing
continues through the repeated opening of the ac-
tivated ring by the monomer anion.
C
O
CH2
R
+
(CH2)n
(CH2)5
Na
C
(CH2)n+2
N
N
NH
R
NH
N C
Study of the structure of the obtained compounds
O
O
CH2
1
by means of H NMR spectroscopy confirms the
C
O
opening of the N-carboxamide imine ring and the
addition of the next molecules. Thus, by the example
of compound IIa (Fig. 4) it is possible to observe the
appearance of new signals in the region of 0.6–
1.2 ppm which belong to the protons of CH2-groups of
the opened imine cycles.
(CH2)5
(CH2)n+2
N
C
O
NH
NH
N
R
(CH2)n+2
etc.
R
N
C
O
The broadening of signals in this spectrum indicates
the presence the studied reaction product of the
Na
Table 1. Yields and molecular-mass characteristics of N-carboxamides and of the reaction productsa
Oligomerization
–
–
–
–
–
Мw
Мn
Мw/Мn
Мcarboxamide
Yield, %
substrate
Iа
51
72
65
59
61
1330
990
290
570
4.6
1.7
1.3
1.2
2.1
224
218
252
372
366
Ib
640
480
Ic
880
730
IIа
2400
1150
IIb
–
a
Mw is weight-average molecular mass, Mn is number-average molecular mass, Mw/Mn is the polydispersity index, Мcarboxamide is molecular
mass of the corresponding N-carboxamide.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

OLIGOMERIZATION OF CYCLIC IMINES N-CARBOXAMIDES
93
hydrogen atoms with different environment, charac-
teristic of the high-molecular compounds with repeat-
ing units. At the same time the spectrum of the
reaction product contains the signals of СН2 group
protons of cyclic structure. A similar observation, in
spite of the symmetrical structure of compound IIa
shows the unequal capability of imine cycles to
opening, which is confirmed by the occupancy nature
of the heterocycles MOs (Fig. 3).
of the reaction products are appreciably different from
the same characteristics of the corresponding mono-
mers (Table 2).
The melting diffusivity indicates the spread of the
molecular mass values of the new compounds. The
diffusivity of the samples Ia and IIb correlates with
their polydispersity indices.
Thus, the oligomerization of cyclic imine N-
carboxamides was carried out in the presence of
anionic type catalyst. It was shown that the products
obtained on the basis of aliphatic N-carboxamides has
higher molecular weight in comparison with the
aromatic substrates.
The values of melting points obtained by the
method of differential-scanning calorimetry also
confirm the fact that the actions of high temperatures
in the presence of compound III leads the formation of
new reaction products. Thus, the melting points values
(а)
(b)
(c)
(d)
Fig. 1. Pictograph image of LUMOs of compounds: (a) Ia, (b) Ib, (c) IIa, and (d) IIb.
(а)
(b)
Fig. 2. Pictograph image of the (a) first and (b) third LUMOs of compound Ib.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

94
FILIPPOVA et al.
(а)
(b)
Fig. 3. Pictograph image of the (a) first and (b) third LUMO of compound IIa.
EXPERIMENTAL
obtained N-carboxamides is confirmed by IR spec-
troscopy. During the reaction progress an absorption
band appeared at 1620 cm–1 [stretching vibrations of
C=O group in amide structures of C(O)–NH type].
The investigation objects are the adducts of
isocyanates of various structure with hexamethylene
imine.
1
Compound Ia. H NMR spectrum, δ, ppm: 1.29 m
Synthesis of N-carboxamide. To 40% DMF
solution of hexamethylene imine was added dropwise
equimolar amount of isocyanate over 30 min. The
reaction mixture temperature was maintained in the
range of 0–4°С by cooling with ice. Then the mixture
was stirred at this temperature to the complete
isocyanate conversion. The residual amount of iso-
cyanate groups was determined by titration [7]. The
obtained precipitate was filtered off, dried in air, and
reprecipitated (chloroform–hexane) for purification.
The obtained products were dried at 50–60°С in a
vacuum to the constant weight.
(4Н, СН2СН2), 1.49 m (6Н, СН2СН2СН2), 1.53 m
(4Н, СН2), 1.55 m (4Н, СН2), 3.16 m (4Н, СН2N),
3.54 m (1Н, СНN), 6.0 s (1H, NH).
Compound Ib. 1H NMR spectrum, δ, ppm: 1.29 m
(4Н, СН2СН2), 1.55 m (4Н, СН2), 3.16 m (4Н, СН2N),
6.0 s (1H, NH), 7.0–7.64 m (5Н, Ar).
1
Compound Ic. H NMR spectrum, δ, ppm: 1.29 m
(4Н, СН2СН2), 1.55 m (4Н, СН2), 3.16 m (4Н, СН2N),
6.0 s (1H, NH), 7.25–7.58 m (4Н, Ar).
Compound IIa. 1H NMR spectrum, δ, ppm: 1.29 m
(8Н, СН2СН2), 1.55 m (8Н, СН2), 2.35 s (3Н, CH3),
3.16 m (8Н, СН2N), 6.0 m (2H, NH), 7.02 s, 7.26 s,
7.90 s (3Н, Ar).
The majority of the cyclic imine N-carboxamides
are soluble in the strong polar solvents. Structure of the
mW
0
2
1
–2
–4
–6
–8
–10
2
1
–12
–14
0 40 60 80 100 120 140 160 180 200 220
9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 δ, ppm
Temperature, °С
Fig. 5. DSC curves: (1) compound IIb and (2) oligomer on
1
Fig. 4. Н NMR spectra (DMSO-d6) of (1) compound IIa
and (2) its oligomerization product.
its base.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 1 2011

OLIGOMERIZATION OF CYCLIC IMINES N-CARBOXAMIDES
95
Table 2. Temperatures of the beginning and equilibrium melting of the reaction products (Tbeg and Teq, respectively) and
melting points of N-carboxamides Tcarboxamide
Tcarboxamide
,
Diffusivity
Oligomerization substrate
Tbeg, ºС
Teq,ºС
ºС
D = Teq – T beg
89
122
152
160
140
115
140
172
167
176
156
117
156
172
140
26
18
20
7
Iа
Ib
Ic
IIа
IIb
36
1
Compound IIb. H NMR spectrum, δ, ppm: 1.29
m (12Н, СН2СН2), 1.55 m (12Н, СН2), 3.16 m (12Н,
СН2N), 6.0 m (2H, NH).
ACKNOWLEDGMENTS
This work was financially supported by the Federal
Targeted Program “Scientific and Scientific-
Pedagogical Potential of Innovative Russia” (2009–
2013) (contract no. P478, 04.08.2009).
ε-Caprolactam sodium salt was obtained as 75%
solution in ε-caprolactam by reaction of the latter with
metal sodium in toluene at 110–112°С to complete
sodium conversion. The obtained product was
precipitated, dried, and stored in a desiccator in a
vacuum.
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