Synthesis and thermal oxidative degradation of quaternized 1,2-dipyridylethanes (-ethylenes) and their oxo derivatives

Article abstract of DOI:10.1134/S1070427210080252

Quaternized compounds derived from 1,2-dipyridylethanes (-ethylenes) and their oxo derivatives were synthesized and characterized. Their thermal degradation was studied, and the dependence of the degradation sequence on the structure of the compounds was examined. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S1070427210080252

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 8, pp. 1454−1460. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © Yu.S. Chekryshkin, N.V. El’chisheva, Zh.A. Vnutskikh, Yu.V. Shklyaev, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83,
No. 8, pp. 1348−1354.
Synthesis and Thermal Oxidative Degradation of Quaternized
1,2-Dipyridylethanes (-ethylenes) and Their Oxo Derivatives
Yu. S. Chekryshkin, N. V. El’chisheva, Zh. A. Vnutskikh, and Yu. V. Shklyaev
Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, Perm, Russia
Received March 10, 2010
Abstract—Quaternized compounds derived from 1,2-dipyridylethanes (-ethylenes) and their oxo derivatives were
synthesized and characterized. Their thermal degradation was studied, and the dependence of the degradation
sequence on the structure of the compounds was examined.
DOI: 10.1134/S1070427210080252
ammonium groups are introduced into polymers with
the aim to control their hydrophilic–lipophilic properties
[8]. Biquaternized dipyridylethylenes are studied as
complexing agents.
Thermal gravimetric (TG) and differential thermal
(DTA) analysis of organic substances is widely used for
studying the thermal stability and degradation sequence
of monomers, polymers, and compounds based on
them [1]. These data are required for the development
of new materials. At the same time, TG and DTA
methods are seldom used for studying quaternized
amines and nitrogen-containing heterocyclic systems,
and interpretation of the thermograms is restricted
to indication of the thermal effects and temperature
range of stability of substances and materials based
on them [2–4]. In the above-mentioned papers, the
sequence of degradation of the quaternary ammonium
compounds is not discussed. Busi et al. [2] studied the
thermal properties of quaternary ammonium halides,
in particular, of dimethyl(ethyl)dioctylammonium
bromides and iodides. The full weight loss of the
samples was observed at temperatures of up to 360°С.
Only endothermic effects caused by polymorphous
transitions, melting, and degradation of the samples are
recorded in the DTA curves. The onset temperature of
the degradation of quaternary ammonium salts increases
in going from bromides to iodides.
Here we report on the synthesis and on thermal and
thermaloxidativedegradationofmono-andbiquaternized
1,2-dipyridylethanes (-ethylenes), α-pyridoin, and
2,2'-pyridil. A study of thermal properties of a wide
range of compounds containing a common fragment
with different anions and substituents at the N atoms
will allow more definite conclusions on the sequence
of fragmentation of molecules containing pyridine and
pyridinium rings. Degradation of molecules can occur
at several bonds simultaneously, but the rates of bond
cleavage can differ. Therefore, from the sample weight
loss is possible to estimate the molecular fragment
formed in the course of decomposition in a certain
temperature interval.
The initial compounds for quaternization were
prepared by oxidative dimerization of α-, β-, and
γ-picolines on strongly basic (В– is melt of NaOH +
V2O5) and acid (А+ is V2O5–K2SO4/SiO2) types [9]
(Scheme 1).
Synthesis of I–III and their antimicrobial activity
have been described previously [5].
Quaternary ammonium salts exhibit antimicrobial
properties [5] and surface activity [2]. Therefore, they
are components of drugs [6], ionic liquids, phase-transfer
catalysts (including those for enantioselective synthesis
[7]), and composite materials [3, 4, 8]. Quaternary
Quaternization was performed following Scheme 2.
The results of differential thermal and thermal
gravimetric analysis of the compounds are given in
1454

SYNTHESIS AND THERMAL OXIDATIVE DEGRADATION
1455
Scheme 1.
N
N
N
N
B_
+
N
N
CH3
II
I
III
N
A+
OH
O
N
N
N
N
+
O
O
V
IV
Scheme 2.
and at 295°С it loses 92% of its weight, whereas the
temperatureintervalinwhich85%ofweightofII.0islost
is 130–305°С, i.e., compound III.0 starts to decompose
at a higher temperature than II.0, but the decomposition
is faster. This fact indicates that an increase in the
conjugation chain between the nitrogen atoms of the
pyridine (pyridinium) rings makes the compounds more
resistant to thermal degradation. Similar trend was
noted in studies of the thermal oxidative degradation of
heterocyclic N-oxides [10, 11].
RX
C
+
X_
N
N
+
R
C
(a)
N
N
2RX
C
+
N
+
N
_
X
X_
Compound IV.0 decomposes in the temperature
interval 145–581°С. Such a wide temperature interval
is characteristic of all the examined quaternized
compounds of this series (see table), which suggests
stepwise mechanism of their degradation, in contrast to
compounds I.0, II.0, and III.0, which decompose in one
step at temperatures of up to 305°С. In the first step, up
to a temperature of 215°С, the weight loss of IV.0 is
24%, which corresponds to the fragment СОН=СОН.
Then, up to 262°С, the weight loss rate decreases
(weight loss 28%), and up to 438°С the weight loss rate
decreases gradually (weight loss 8%). In the range 438–
581°С, the weight loss rate increases, with the weight
loss amounting to 36%. Apparently, breakdown of one
pyridineringwiththereleaseoftheСОН=СОН fragment
is accompanied by protonation of the nitrogen atom of
the second ring, which decomposes in the temperature
interval 400–582°С, with 36% weight loss. The last
step of the weight loss of all the examined quaternized
pyridine derivatives occurs in approximately the same
temperature interval. The other fragments that could be
R
R
(b)
C = СН2–СН2, position 3 (I); СН=СН, position 3 (II),
position 4 (III); (НО)СН–СО, position 2 (IV); ОС–СО,
position 2 (V); I.0*: R = 0 (I.0); Ia: R = C14H29, X = Cl
(Ia.1); R = C16H33, X = Cl (Ia.3); R =СН2СОС6Н5, Х =
I (Ia.4); Ib: R = C12H25, X = Br (Ib.2); R = C14H29, X =
Cl (Ib.1); R = C16H33, X = Cl (Ib.3); R =СН2СОС6Н5,
Х = I (Ib.4); II.0*: R = 0 (II.0); IIa: R = CH2CH=CH2,
X = Cl (IIa.1); R = C14H29, X = Сl (IIa.2); R = C16H33,
X = Cl (IIa.3); IIb: R = CH2CH=CH2, X = Br (IIb.1);
R = C12H25, X = Br (IIb.2); R =СН2СОС6Н5, Х = I
(IIb.3); III.0*: R = 0; IIIa: R = C14H29, X = Br (IIIa.1);
IIIb: R = C16H33, X = Cl (IIIb.1); IV.0: R = 0; IVа:
R = C16H33, X = Cl (Va.1); V.0*: R = 0; nonquaternized
compounds are marked with an asterisk.
the table. As can be seen, degradation of II.0 starts at
a 10°C higher temperature compared to I.0; the same
is true for their quaternized derivatives. Compounds
Iа.3 and IIа.3 are exceptions. In turn, compound III.0
starts to decompose at a higher temperature, 160°С,
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1456
CHEKRYSHKIN et al.
formed in degradation of α-pyridoin are removed before
this temperature interval is reached.
atom bears an alkyl substituent, degradation of the
molecules starts with fragmentation of the substituent,
which is followed by cleavage of the С–С bond and
formation of two fragments containing pyridinium
rings. The fragments containing quaternized nitrogen
atom, formed in the course of degradation, remain in
the condensed phase, and their oxidation, as well as
oxidation of the coke formed, is manifested as a strong
broad exothermic peak at 400–570°С in the DTA curves
of all the examined quaternized compounds.
The TG curves of V.0 and IV.0 are similar.
Compound V.0 decomposes in the temperature interval
from 157–227 to 411–582°С. On heating to 227°С,
the sample weight loss is 36%, which corresponds to
removal of one pyridine ring. The endothermic effect is
recorded at 156°С (melting), and the exothermic effects,
at 162 and 461°С (broad). The results of studying the
thermal properties suggest that the degradation of IV.0
starts with the cleavage of pyridyl–СНОН bonds, and
in the molecule of V.0, because of symmetrical electron
distribution, the СО–СО bond is cleaved first.
The thermogram of 1,2-bis(N-allylpyridinium-3-yl)
ethylenedibromideIIb.1isshowninthefigure.Ascanbe
seen, degradation in the temperature interval 185–220°С
occurs with 7% weight loss. Presumably, degradation
of the molecule occurs at bonds linking the ethylene
fragment with the pyridinium moiety. The sample weight
does not change in the temperature interval 220–250°С,
which is followed by the weight loss, more gradual than
in the first step. The weight loss on heating to 375°С
corresponds to breakdown of the pyridyl rings, and
heating to 570°С causes decomposition of the fragment
containing bromide ion and quaternized nitrogen atom.
All the steps of degradation of IIb.1 are well resolved.
Exothermic effects are recorded at 225, 260, 305, 347,
354, and 358°С, and a broad peak is recorded at 470°С.
The degradation onset temperature for quaternized
dipyridylethanes (-ethylenes) is higher than that
for the starting bases. For example, compound II.0
starts to decompose at 130°С, whereas its derivative
monoquaternized with allyl chloride (IIа.1) decomposes
after melting at 148°С, i.e., the presence of an electron-
deficient nitrogen atom in the molecules of the
compounds under consideration enhances their thermal
stability. The derivatives obtained by quaternization
of the pyridine nitrogen atoms with cetyl chloride are
exceptions: The degradation onset temperature for these
compounds (IIа.3, IIIb.1, IVа.1) is lower than that of the
respective bases, which may be due to limited thermal
stability of the cetyl substituent.At the same time, higher
degradation onset temperature for α-pyridoin IV.0
(145°C), compared to its derivative monoquaternized
with cetyl chloride (118°С), may be due to stabilization
of the endiol form of the α-pyridoin molecule as a result
of formation of hydrogen bonds [12] and distortion of
the molecular symmetry upon quaternization.
In argon, the weight loss starts at 192°С, and on
heating to 236°С it reaches 15.6%. Then the weight
loss rate decreases, and at 500°С the residual sample
weight in the crucible is 37%. In the DSC curve of this
compound, there is an endothermic effect at 186°С,
corresponding to the sample melting. The thermal effect
of this process is 2.4 kJ mol–1. Endothermic effects
Δm, g
The thermal stability and degradation sequence
of the compounds depends on the kind of halogen,
structure of the substituent at the quaternary nitrogen
atom, conjugation between the rings, and symmetry of
the electron density distribution in the molecule.
DTG
Degradation of dipyridylethanes (-ethylenes)
quaternized with alkyl bromides starts at a higher
temperature than the degradation of the corresponding
chlorides, which is consistent with the results of thermal
analysis of quaternized alkylamines [2].
DTA
TG
Ifthequaternizednitrogenatombearsallylsubstituent,
degradation of biquaternized dipyridylethanes starts
with the cleavage of the С–С bond in the ethane bridge
between the pyridinium rings, which is followed by
breakdown of the rings. If the quaternized nitrogen
T, °C
Thermogram of 1,2-bis(N-allylpyridinium-3-yl)ethylene
dibromide in air. (Δm) Weight change and (T) temperature.
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SYNTHESIS AND THERMAL OXIDATIVE DEGRADATION
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010

1458
CHEKRYSHKIN et al.
were also noted at 207 and 290°С (broad). Because of
the absence of oxygen, no exothermic effects due to
oxidation of the fragments formed are observed.
0.4 kJ mol–1) is manifested at 326°С.
Compound Ia.4, dipyridylethane monoquaternized
with phenacyl iodide, undergoes multistep thermal
oxidative degradation. The process starts at 160°С,
and on heating to 324°С the weight loss is 40%
(171 amu). Then the degradation rate decreases, but in
the temperature interval 364–376°С it sharply increases.
The sample weight loss in this step is 14%, which is
attributable to the breakdown of the pyridinium ring.
On heating to 584°С, the fragment containing the
quaternized nitrogen atom and iodide ion undergoes
gradual oxidative degradation accompanied by a broad
exothermic effect.
The IR spectra of the gaseous products formed by
thermal degradation of Iа.4, IIа.1, and IIb.1 in argon do
not change in the temperature interval from the melting
point to 367°С; only the band intensities increase. The
observed bands suggest the presence of compounds
with triple С≡С, –С≡N bonds (2392–2333 cm–1) and of
conjugated olefins and aromatic compounds (series of
С=С bands at 1600, 1580, 1500, and 1450 cm–1, with
the band at 1500 cm–1 being more intense than the band
at 1600 cm–1). The results obtained show that partial
degradation of the molecules, with vaporization of
fragments formed, is observed already on melting. The
following scheme of thermal degradation of IIb.1 can
be suggested:
Under argon, decomposition of Iа.4 also starts at
160°С. The weight loss is 36% on heating to 265°С and
74% on heating to 350°С. In the interval 160–224°С,
there are two ill-resolved endothermic peaks. The total
thermal effect corresponding to them is 51.5 kJ mol–1.
Endothermic effects are also observed at 320 and 502°С.
Monoquaternized 1,2-dipyridylethane (-ethylene)
derivatives undergo degradation in a wider temperature
interval than the biquaternized derivatives. For example,
compound Iа.3 decomposes in the temperature interval
155–535°С, whereas the degradation of Ib.3 is
observed in the interval 170–455°С. The thermogram
of biquaternized derivative Ib.1 is simpler than that of
the monoquaternized compound Ia.1. This fact indicates
that, after the cleavage of the С–С bond between the
rings (170–268°С), the two similar fragments formed
decompose simultaneously without formation of steps
in the TG curve, except the step of thermal degradation
of fragments containing the quaternized nitrogen atom
in the temperature interval 268–440°С. Compound
Iа.1 decomposes in several steps. In the TG curve,
one can distinguish steps of the decomposition of the
alkyl substituent (155–280°С), pyridine and pyridinium
rings (280–485°С), and fragment with the quaternized
nitrogen atom (485–560°С). The endo- and exothermic
effects accompanying thermal decomposition of alkyl
radicals are, as a rule, insignificant because of partial
compensation of the thermal effects of degradation and
vaporization, on the one hand, and oxidation, on the
other hand.
+
N
+
N
_
Br _
CH=CH
Br
N
Br_
+
_
+
N
2
+
BrH
CH
According to DTA, melting of dipyridylethylene
monoquaternized with allyl chloride (IIа.1) starts at
148°C, and the degradation starts at 168°С. Further
increase in temperature to 305°С leads to 93% weight
loss without pronounced steps. Then, on heating to
450°С, the remaining 5 wt % of the sample is oxidized,
as indicated by a broad peak in the interval 400–445°С.
In an argon medium (DSC method), degradation of
IIа.1 also starts at 168°С, and on heating to 294°С
the sample weight loss is 94.5%; the melting point is
154°С (ΔН = 31.0 kJ mol–1). Furthermore, in the DSC
curve in the interval 168–294°С there is an endothermic
effect (ΔН = 98.8 kJ mol–1). When the degradation
is performed in air, this peak is absent because of its
compensation by exothermic processes of oxidation of
the products formed. A weak endothermic effect (ΔН =
Biquaternized 1,2-bis(3-pyridyl)ethylene deriva-
tives start to degrade at a higher temperature than
monoquaternized derivatives, with the release of the
СН=СН fragment. Degradation of unsymmetrical
monoquaternized 1,2-bis(3-pyridyl)ethylenes starts with
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SYNTHESIS AND THERMAL OXIDATIVE DEGRADATION
1459
the decomposition of alkyl substituents at the nitrogen
atom, followed by bond cleavage in the ring. In the
process, the endothermic effect of the bond cleavage is
compensated by the exothermic effect of the oxidation
of the fragments formed. The exothermic effects have
maxima at 255–300 (small peak) and 400°С.
CH2–N+); 7.98 t (2H, H5-py); 8.66 d (2H, H4-py); 9.06 d
(2H, H6-py); 10.11 s (2H, H2-py). Yield 12.4%, mp 135–
137°С. Found, %: С 72.05, Н 10.59, N 4.21. Calculated,
%: С 73.96, Н 10.79, N 4.31.
1-(N-Tetradecylpyridinium-3-yl)-2-(3-pyridyl)
ethylene chloride (IIa.2). 1Н NMR spectrum (CDCl3),
δ, ppm: 0.85 t (3Н, СН3); 1.24 m (22Н, СН2); 1.75 m
(2Н, β-CH2); 4.95 d (2Н, +N–CH2); 7.15 s (1Н, Н=CH);
7.24 s (1Н, Н=СН); 7.31 t (1Н, Н5'-Py); 7.39 t (1Н, Н5-Py);
7.63 d (1Н, Н4'-Py); 8.41 d (1Н, Н6'-Py); 8.70 s (1Н, Н2'-Py);
8.78 d (1Н, Н4-Py); 9.00 d (1Н, Н6-Py); 10.45 s (1Н, Н2-Py).
Yield 7.24%, mp 180°С with decomposition. Found, %:
С 75.20, Н 9.39, N 6.68.Calculated, %: С 75.24, Н 9.47,
N 6.75.
EXPERIMENTAL
The IR spectra were recorded on an IFS 66 Fourier
1
transform IR spectrometer, and the Н NMR spectra,
on a Mercury plus 300 spectrometer (Varian) operating
at 300 MHz, with TMS as internal reference. Elemental
analysis was performed with a CHNS-932 device
(LECO Corporation, USA). The reaction progress was
monitored by TLC on Silufol UV-254 plates using
the system ethanol–chloroform–acetone (3 : 1 : 0.1)
+ two drops of H2SO4 per 10 ml of the mixture. The
chromatograms were visualized in an iodine chamber
or by UV. Thermal gravimetric analysis was performed
with a Q-1500D derivatograph at a heating rate of
2.5 deg min–1 in Alundum crucibles in air, and also
with an STA 449C Jupiter Fourier transform device
(Netzsch) at a heating rate of 2.5 deg min–1 under
argon (the device allows simultaneous recording of the
thermogram and DSC curve with analysis of the gas
phase).
1-(N-Tetradecylpyridinium-4-yl)-2-(4-pyridyl)
ethylene chloride (IIIa.1). 1Н NMR spectrum
(DMSO-d6), δ, ppm: 0.86 t (3Н, CH3); 1.20 m (22Н,
CH2); 1.96 m (2Н, β-СH2); 4.86 t (2Н, СH2–N+); 7.38 s
(1Н, =СH); 7.53 d (2Н, Н3',5'-py); 7.79 s (1Н, =СH);
8.31 d (2Н, Н2',6'-py); 8.63 d (2Н, Н3,5-py); 9.35 d (2Н, Н2,6-
py). Yield 3.62%, mp 170–172°С. Found, %: С 75.27,
Н 9.14, N 6.75. Calculated, %: С 75.24, Н 9.47, N 6.75.
1-(N-Cetylpyridinium-2-yl)-2-(2-pyridyl)-2-
oxoethanol chloride (IVa.1). 1Н NMR spectrum
(CDCl3), δ, ppm: 0.98 t (3Н, СН3); 1.23 m (26Н, СН2);
1.99 t (2Н, β-СН2); 2.60 m (2Н, СН2); 4.97 t (1Н, СН2–
N+); 4.37 t (1Н, СН2–N+); 7.31 t (1Н, Н4'-ру); 7.6 d (1Н,
Н6'-ру); 7.94–7.97 m (2Н, Н4,5'-ру); 8.09 d (1Н, Н3'-ру);
8.16 d (1Н, Н6-ру); 8.16 t (1Н, Н5-ру); 8.54 d (1Н, Н3-ру).
Yield 8.5%, greasy substance.
Quaternization (general procedure). Equimolar
amounts of the starting compounds I–IV and halo
derivative were dissolved in acetonitrile and heated
for 5–72 h. The mixture was allowed to stand at room
temperature for 10–20 h. The resulting precipitate was
separated and washed with acetone or recrystallized
from water.
CONCLUSIONS
(1) The onset temperature and sequence of
degradation of 1.2-dipyridylethanes (-ethylenes) and
their quaternized derivatives are determined by the
symmetry of the electron distribution in the molecule,
by the presence or absence of conjugation between the
nitrogen atoms, by the structure of the substituent at the
quaternized nitrogen atom, and by the kind of the halide
ion, in agreement with the available data on thermal
degradation of related compounds.
1-(N-Tetradecylpyridinium-3-yl)-2-(3-pyridyl)
ethane chloride (Ia.1). 1Н NMR spectrum (СDCl3 ), δ,
ppm: 0.85 t (3Н, СН3); 1.23 m (22Н, СН2-alk); 1.71 m
(2Н, β-СН2); 3.01 t (2Н, СН2); 3.16 t (2Н, СН2); 4.56 t
(2Н, СН2–N+); 7.31t (1Н, Н5'-Py); 7.63 d (1Н, Н4'-Py);
8.09 t (1Н, Н5-Py); 8.41 d (1Н, Н6'-Py); 8.48 d (1Н, Н4-Py);
8.50 d (1Н, Н6-Py); 9.11 s (1Н, Н2'-Py); 9.35 s (1Н, Н2-Py).
Yield 23.6%, mp 150°С with decomposition. Found,
%: С 74.69, Н 9.78, N 6.83. Calculated, %: С 74.87,
Н 9.91, N 6.72.
(2) Quaternization leads to an increase in the
thermal stability of dipyridylethanes (-ethylenes). The
degradation onset temperature for the biquaternized
derivatives is higher than for the monoquaternized
derivatives, but the temperature interval of the
degradation for the latter compounds is broader.
1,2-Bis(N-tetradecylpyridinium-3-yl)ethane
dichloride (Ib.1). 1Н NMR spectrum (CDCl3), δ, ppm:
0.86 t (6Н, CH3); 1.23 t (44H, CH2); 2.03 t (4H, β-СН2);
2.76 t (4Н, СН2-alk); 3.57 t (4Н, СН2–СН2); 4.77 t (4H,
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CHEKRYSHKIN et al.
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the examined compounds was suggested.
7. Ayyanar, S. and Eagambaram, M., J. Mol. Catal. A, 2006,
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