Synthesis and characterisation of new Schiff base monomers containing N-(alkyl and phenyl) pyrrole moieties

Article abstract of DOI:10.1016/j.molstruc.2017.06.067

This article deals with the synthesis and characterisation of seven new functional Schiff base monomers, such as: M1: 1-(3-Pyrrole-1-yl-propylimino-methyl)-naphtalen-2-ol; M2: 2-(3-Pyrrole-1-yl-phenylimino-methyl)-phenol; M3: 1-(3-Pyrrole-1-yl-phenylimino-methyl)-naphtalen-2-ol; M4: N-(pyridin-2-yl-methylene)-2-(pyrrol-1-yl)-benzenamine; M5: N-(pyridin-2-yl-methylene)-3-(pyrrol-1-yl)-propan-1-amine; M6: 2-(3-pyrrol-1-yl-propylimino-methyl)-quinolin-8-ol; M7: 2-(3-pyrrol-1-yl-phenylimino-methyl)-quinolin-8-ol. Two series of compounds emerged from this study, N-propyl pyrrole derivatives (M1, M5, M6) and N-phenyl pyrrole compounds (M2, M3, M4, M7). All monomers were elaborated by condensation reactions between appropriate amines and aldehydes, and their molecular structures were confirmed by spectroscopic analysis methods like FT-IR, ¹H NMR, ¹³C NMR, and GC-MS.

Full text of DOI:10.1016/j.molstruc.2017.06.067

Accepted Manuscript
Synthesis and Characterization of New Schiff Base Monomers Containing N-(alkyl
and phenyl) Pyrrole Moieties
Ahcene Ait Amer, Hocine Ilikti, Ulrich Maschke
PII:
S0022-2860(17)30848-7
10.1016/j.molstruc.2017.06.067
MOLSTR 23953
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
02 January 2017
13 June 2017
15 June 2017
Please cite this article as: Ahcene Ait Amer, Hocine Ilikti, Ulrich Maschke, Synthesis and
Characterization of New Schiff Base Monomers Containing N-(alkyl and phenyl) Pyrrole Moieties,
Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.06.067
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ACCEPTED MANUSCRIPT
Synthesis and Characterization of New Schiff Base Monomers Containing
N-(alkyl and phenyl) Pyrrole Moieties
Ahcene Ait Amer a, b, c, Hocine Ilikti , and Ulrich Maschke *
b
a,
a) Unité Matériaux et Transformations – UMET (UMR CNRS N°8207), Bâtiment C6,
Université Lille 1 - Sciences et Technologies, 59655 Villeneuve d’Ascq Cedex, France
b) Laboratoire de Chimie et d’Electrochimie des Complexes Métalliques (LCECM),
Université des Sciences et de la Technologie d’Oran Mohamed Boudiaf (USTO-MB), BP
1
505, El-M’naouer, 31000 Oran, Algeria
c) Département de Chimie, Faculté des Sciences, Université Djilali Liabès (UDL), BP 89,
2000 Sidi-Bel-Abbès, Algeria
2
Fax : 0033 3 20 43 65 91 ; e-mail : ulrich.maschke@univ-lille1.fr
1

ACCEPTED MANUSCRIPT
Abstract
This article deals with the synthesis and characterization of seven new functional Schiff base
monomers, such as : M1: 1-(3-Pyrrole-1-yl-propylimino-methyl)-naphtalen-2-ol; M2: 2-(3-
Pyrrole-1-yl-phenylimino-methyl)-phenol;
naphtalen-2-ol; M4: N-(pyridin-2-yl-methylene)-2-(pyrrol-1-yl)-benzenamine; M5: N-
pyridin-2-yl-methylene)-3-(pyrrol-1-yl)-propan-1-amine; M6: 2-(3-pyrrol-1-yl-propylimino-
M3:
1-(3-Pyrrole-1-yl-phenylimino-methyl)-
(
methyl)-quinolin-8-ol; M7: 2-(3-pyrrol-1-yl-phenylimino-methyl)-quinolin-8-ol.
Two series of compounds emerged from this study, N-propyl pyrrole derivatives (M1, M5,
M6) and N-phenyl pyrrole compounds (M2, M3, M4, M7). All monomers were elaborated by
condensation reactions between appropriate amines and aldehydes, and their molecular
1
13
structures were confirmed by spectroscopic analysis methods like FT-IR, H NMR, C NMR,
and GC-MS.
Keywords: N-pyrrole derivatives; Schiff base; functional monomers; spectroscopy.
2

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1
. Introduction
Pyrrole and its derivatives represent an important class of heterocyclic compounds in organic
chemistry, due to their presence during the synthesis of pharmaceutical, biological,
agricultural, and active natural products, as well as functional starting materials to elaborate
organic semi-conductors [1,2].
One of the most important derivatives, the N-alkyl pyrroles or N-disubstituted pyrroles, were
employed as monomers for the preparation of conducting polymers [3-6], as chelating agent
for the synthesis of coordinating ligands [7,8], and for the preparation of chemical and bio-
sensors [9-11]. In particular, these monomers were applied as modified electrodes used as
mediators in electrocatalytic reactions [12].
For these reasons research efforts are actually carried out worldwide to develop new
structures including N-alkyl pyrrole moieties. Various synthetic pathways are reported in
literature, such as the Clausen Kass method involving 2,5-dimethoxytetrahydrofuran as four-
carbon source condensed with a primary amine [13,14], and many other methods like
Hantzsch-Feist, and Paal-Knorr [15-18]. N-alkyl pyrrole moieties of controlled molecular
architecture can be engineered for their desired applications. For example, N-alkyl pyrrole
polymerizes electrochemically since the positions two and five on the pyrrole molecule are
free to allow evolution to polymeric chains on these positions. Furthermore, membranes can
be prepared as well as modified electrodes (ME), used in catalytic applications by
electrodeposition of functionalized pyrrole (N-[3-(dimethylpyridyl-2-yl)aminopropyl], N-(3-
aminopropyl), N-(3-acetamidopropyl) and N-(2-cyanoethyl)) [19]. Structures used as
coordinating ligands could also be achieved, by attachment of the pyrrole on a functional
moiety to obtain ML-type coordination compounds (M: metal, L: ligand), as it is the case for
bipyridyl-pyrrole [20] and N,N-bis (2-pyrrole) N-methylamine (BPEMA) [21].
3

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In this report more versatile modified electrodes were elaborated and several functional
groups were introduced and attached on the N-alkyl pyrrole, including the azomethine group
more known as Schiff base. These compounds allow coordination with a large variety of
metal ions, especially transition metals like copper to obtain complexes designated for
different applications. Only a few records on N-alkyl pyrrole containing Schiff bases are
reported in the literature, such as the synthesis and characterization of 6-[3′-N-pyrrole
propoxy]-2-hydroxyacetophenone combined with 1,2-diaminoethane, corresponding to a
derivative of N-substituted pyrrole salicylaldehyde, and their copper complexes [22-23]. The
synthesis of Schiff base of N-(3-aminopropyl)pyrrole-salicylaldehyde was also reported [24-
2
5].
However, the synthesis of the compounds mentioned above requires a large number of
sequential reaction steps and the use of many solvents and organic products. For all these
reasons and the importance of these derivatives in terms of their advantages and applications,
this work aims to elaborate seven new Schiff base compounds, containing pyrrole moieties
with coordination sites. It will be shown that these manifold structures could be synthesized in
high yield and purity by simple condensation reactions between appropriate amines and
aldehydes.
4

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2
. Experimental part
2
.1 Materials
Ethanol was purchased from Merck (absolute grade for analysis); hexane, acetone, diethyl
ether and petroleum ether were purchased from Aldrich (p.a. grade solvents). Magnesium
sulphate, sodium hydroxide, sodium chloride, Lithium aluminium hydride (LiAlH ), N-(2-
4
cyanoethyl)
pyrrole
(NCPy),
2-hydroxy-1-naphtaldehyde,
salicylaldehyde,
2-
pyridinecarboxaldehyde, 8-Hydroxy-2-quinoline-carboxaldehyde, and 1-(2-aminophenyl)
pyrrole were obtained from Sigma Aldrich. All these reagents were used as received.
2
.2 Instrumentation
Fourier Transform Infrared spectra (FTIR) were recorded in ATR mode using a Perkin Elmer
-1
-1
Frontier model spectrometer between 4000 cm and 600 cm with a spectral resolution of 4
-1
cm over 16 scans.
The melting points were determined by Differential Scanning Calorimetry on a Perkin Elmer
DSC 8000 apparatus. Temperature and heat flow scales were calibrated with high purity
indium standards. Samples of about 5mg were analyzed under nitrogen gas flow at a heating
rate of 10°C/min from -72°C to 230°C. At least two samples were analyzed for each
compound to verify reproducibility of the results. The melting temperatures were taken from
the end of the melting peaks.
1
13
H- and C-NMR spectra were recorded in appropriate deuterated solvents (concentration
6
mg/10mL) with tetramethylsilane as internal standard, using a Bruker AC 300MHz
spectrometer.
The Gas Chromatography/Mass Spectrometry (GC/MS) analysis was performed on a Perkin
Elmer Clarus 680 gas chromatograph coupled with a Clarus 600T mass detector
5

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(PerkinElmer, Shelton, USA). The gas chromatograph was equipped with a quadripole mass
analyser (QSM). Elite-5HT (5% diphenyl, 95% dimethylpolysiloxane) capillary column of
0m length × 0.25µm ID with film thickness 0.10µm (PerkinElmer, Shelton, USA) was
employed. The injector temperature was 300°C and a 10μL syringe was used for injections of
.2μL. Helium was the carrier gas, with a constant flow of 1.5mL/min. The Electron
3
0
ionization (EI) was used with an ion source temperature of 180°C and an interface
temperature of 300°C. The furnace temperature was maintained at 70°C for 15min, then rises
to 150°C with a rate of 20°C/min followed by an isotherm of 10min, then rises to 240°C
followed by an isotherm of 10min.
2
.3 General procedure for the synthesis of the monomers
2
.3.1 Synthesis of 1-(3-aminopropyl) pyrrole (APP)
The APP monomer was synthesised by catalytic reduction of N-(2-cyanoethyl) pyrrole
NCPy) (Fig. 1) as previously described [5,10]. In brief, 33.2mmol (1.26g) of LiAlH were
(
4
dispersed in 100mL of anhydrous diethyl ether for 30min by ultrasonic dispersion. In a three-
necked flask (500mL), 16.6mmol (5.2g) of N-(2-cyanoethyl) pyrrole (NCPy) were dissolved
in 20mL of anhydrous diethyl ether. The dispersed LiAlH was slowly added under vigorous
4
magnetic stirring. The mixture was then heated under reflux conditions (~35°C) for 20h.
Fig. 1. Synthesis of 1-(3-aminopropyl) pyrrole (APP).
After cooling, the excess hydride was destroyed by successive addition of 3.4mL of ultra pure
water, 3.4mL of 15% aqueous NaOH solution, followed by slow addition of 10mL of ultra
6

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pure water. The solution was then heated to 40°C for 4h and filtered on MgSO . After rotary
4
evaporation, a yellow oily APP product was obtained and dried in vacuum.
The product appearance: light-yellow viscous oil, yield: 78.38%, refractive index:
nD(20°C)=1.5217.
-1
FTIR (ATR) ν (cm ): 3369- 3292 (NH ), 3090 (aromatic C-H stretch), 2950 and 2870
2
(aliphatic C-H stretch), 1503 (N-H out of plane deformation), 1300 (N-ring stretch), 1280 (C-
N stretch) and 750 (C-H out of plane).
1
1
2
H-NMR (300 MHz, CDCl ) δ (ppm): 6.55 (s, 2H , C-H pyrrole), 6.04 (s, 2H , C-H
3
3
3
3
5
pyrrole), 3.87 (t, J=6.94Hz, 2H , CH ), 2.60ppm (t, J=6.84Hz, 2H , CH ), 1.80 (p,
2
2
3
4
6
J=6.88Hz, 2H , CH ), 1.22 (s, 2H , NH ).
2
2
1
3
1
2
C-NMR (75 MHz, CDCl ) δ (ppm): 120.53 (C , pyrrole), 108.06 (C , pyrrole) and 47.35
3
3
5
4
(
C ), 39.07 (C ), 34.53 (C ) aliphatic CH carbons.
2
+
+
+
+
MS (ES ): 124 (M ), 81 (C H N , base peak). Accurate mass (ES ): 124.145, calculated:
5
6
1
24.184.
2
.3.2 Synthesis of monomer M1: 1-(3-Pyrrole-1-yl-propylimino-methyl)-naphtalen-2-ol
In general, the monomers were synthesized by reproducing the same synthesis protocol with
appropriate aldehydes and amines, so in the following the synthesis method of the monomer
M1 will be given, which represents the synthetic pathway of the other monomers as well (see
Fig. 2 and their structures in Fig. 3).
In a three-necked flask 10mmol (1.72g) of 2-hydroxy-1-naphtaldehyde were dissolved in
1
5mL of absolute ethanol under thermal agitation, and 10mmol (1.24g) of 1-(3-aminopropyl)
pyrrole (APP) was added using the same volume of absolute ethanol. The mixture was then
kept under nitrogen atmosphere and heated under reflux (~78°C) for 3h. After cooling, the
7

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solvent was removed with a rotator evaporator and the crude product was purified by column
chromatography using a mixture of petroleum ether-acetone (3:1) as eluent, revealing high
purity of the compound.
Fig. 2. Synthesis route of monomer M1.
The product appearance: brown viscous oil, yield: 82.13%.
-1
FTIR (ATR) ν (cm ): 3300 (broad, OH aromatic), 3097 and 3055 (aromatic C-H stretch),
965 and 2870 (aliphatic C-H stretch), 1630 (C=N), 1550, 1525 and 1490 (aromatic C-C
stretch), 1357 (C-N stretch), 1270 (=C-OH phenolic), 825 and 720 (C-H out of plane).
2
1
H-NMR (300 MHz, CD OD) δ (ppm): 10.89 (s, 1H, OH phenolic), 8.89 (s, 1H, H6,
16
3
1
4
9
HC=N), 7.99 (d, J=8.32Hz, 1H, H aromatic), 7.77 (d, J=8.32Hz, 1H, H aromatic), 7.62 (m,
1
2
10
11
1
H, H aromatic), 7.46 (ddd, J=8.41, 7.04, 1.47Hz, 1H, H aromatic), 7.24 (m, 1H, H
1
5
1
2
aromatic) , 6.82 (d, J=9.38Hz, 1H, H aromatic), 6.75 (s, 2H , C-H pyrrole), 6.12 (s, 2H , C-
3
5
H pyrrole), 4.09 (t, J=6.70Hz, 2H , CH ), 3.60 (t, J=6.77Hz, 2H , CH ), 2.24 (p, J=6.76Hz,
2
2
4
2
H , CH ).
2
1
3
16
6
C-NMR (75 MHz, CD OD) δ (ppm): 180.68 (C , C-OH phenolic), 160.66 (C , C=N),
3
1
4
8
10
12
13
11
10
1
1
39.84(C ), 135.82(C ), 130.18(C ), 129.44(C ), 127.32(C ), 126.19(C ), 123.84(C ),
1
5
7
1
2
19.37(C ), 109.84(C ), all aromatic carbons, 121.52(C , pyrrole), 109.17(C , pyrrole), and
8

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3
5
4
5
8.35(C ), 47.14(C ), 33.13(C ) aliphatic CH carbons.
2
+
+
+
+
MS (ES ): 278 (M ), 198.241 (C H NO , base peak). Accurate mass (ES ): 278.222,
1
3
12
calculated: 278.142.
Fig. 3. Structure of 1-(2-aminophenyle) pyrrole (APP) and Schiff base monomers (M1-M7).
9

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2
.3.3 Synthesis of monomer M2: 2-(3-Pyrrole-1-yl-phenylimino-methyl)-phenol
The monomer M2 was prepared in the same manner as M1, with 3.1mmol (0.38g) of
salicylaldehyde and an equivalent of 1-(2-aminophenyl) pyrrole (0.5g). At the end of the
reaction and after cooling, the precipitated product was filtered and washed with cold ethanol,
and finally dried in vacuum.
The product appearance: yellow crystalline solid; yield: 59.17%; m =169.55°C (determined
p
by DSC).
-1
FTIR (ATR) ν (cm ): 3290 (OH aromatic), 3098 and 3051 (aromatic C-H stretch), 1610
C=N), 1587, 1518 and 1472 (aromatic C-C stretch), 1338 (C-N stretch), 1226 (=C-OH
(
phenolic), 759, 733 and 720 (C-H out of plane).
1
9
H-NMR (300 MHz, acetone-D ) δ (ppm): 8.73 (s, 1H, H , HC=N), 7.51 (d, J=7.87Hz, 1H,
6
4
11
5
H aromatic), 7.40 (dd, J=1.56, 7.87Hz, 1H, H aromatic), 7.15 (td, J=1.68, 8.01Hz, 1H, H
7
1
aromatic), 7.04 (dd, J=1.59, 7.61Hz, 1H, H aromatic), 6.97 (d, J=1.11, 4.04Hz, 2H, H , C-H
1
4
6
pyrrole), 6.90 (dd, J=1.09, 8.09Hz, 1H, H aromatic), 6.84 (m, 1H, H aromatic), 6.78 (td,
1
3
12
15
J=1.14, 7.48Hz, 1H, H aromatic), 6.23 (m, 1H, H aromatic), 5.88 (s, 1H, OH phenolic),
2
5
.73 (d, J=4.87Hz, 2H, C-H pyrrole).
1
3
15
9
C-NMR (75 MHz, acetone-D ) δ (ppm): 178.58(C , C-OH phenolic), 161.29(C , C=N),
6
8
13
03
05
06
04
07
1
1
32.94(C ), 130.26(C ) 129.18(C ), 129.08(C ), 126.71(C ), 120.04(C ), 118.78(C ),
1
2
10
14
1
2
17.82(C ), 115.59(C ), 115.44(C ), all aromatic carbons, 119.60(C , pyrrole), 111.57(C ,
pyrrole).
+
+
+
+
MS (ES ): 262 (M ), 260.247 (C H N O , base peak). Accurate mass (ES ): 262.298,
1
7
12
2
calculated: 262.306.
1
0

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2
.3.4 Synthesis of monomer M3: 1-(3-Pyrrole-1-yl-phenylimino-methyl)-naphtalen-2-ol
The monomer M3 was prepared in the same manner as M1, with 3.1mmol (0.53g) of 2-
hydroxy-1-naphtaldehyde and an equivalent of 1-(2-aminophenyl) pyrrole (0.5g). The solvent
used in this reaction was methanol. At the end of the reaction and after cooling, the
precipitated product was filtered and washed with cold ethanol, and finally dried in vacuum.
The product appearance: white - yellow solid; yield: 48.50 %; m =193°C (determined by
p
DSC).
-1
FTIR (ATR) ν (cm ): 3360 (broad, OH aromatic), 3064 (aromatic C-H stretch), 1625 (C=N),
1
510, 1463 and 1420 (aromatic C-C stretch), 1310 (C-N stretch), 1240 (=C-OH phenolic),
8
12 and 742 (C-H out of plane).
1
9
H-NMR (300 MHz, acetone-D ) δ (ppm): 9.76 (s, 1H, H , HC=N), 8.09 (d, J=8.6Hz, 1H,
6
1
2
4,15
13
H aromatic), 7.86 (d, J=8.50Hz, 2H, H aromatic), 7.61 (d, J=7.70Hz, 1H, H aromatic),
.44-7.34 (m, 3H, H14,15,7 aromatic), 7.19-6.99 (m, 4H, 2C-H pyrrole, H aromatic), 6.56
2
17,6
7
2
19
(
m, 2H, C-H pyrrole 2H), 5.28 (s, 1H, OH ).
1
3
9
19
C-NMR (75 MHz, acetone-D ) δ (ppm): 157.68(C , C=N), 140.16(C , C-OH phenolic),
6
8
17
3
16
11
10
7
1
1
1
38.52(C ), 134.78(C ), 130.67(C ), 130.65(C ), 129.76(C ), 19.51(C ), 128.36(C ),
1
5
12
13
14
6
1
28.15(C ), 127.95(C ), 125.57(C ), 124.81(C ), 123.19(C ), 122.66(C , pyrrole),
5
18
4
2
20.86(C ), 118.98(C ), 117.44(C ), 110.13(C , pyrrole).
+
+
+
+
MS (ES ): 312 (M ), 311.230 (C H N O , base peak). Accurate mass (ES ): 312.255,
3
1
15
2
calculated: 312.365.
1
1

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2
.3.5 Synthesis of monomer M4: N-(pyridin-2-yl-methylene)-2-(pyrrol-1-yl)-benzenamine
The monomer M4 was prepared in the same manner as M1, with 3.1mmol (0.34g) of 2-
pyridinecarboxylaldehyde and an equivalent of 1-(2-aminophenyl) pyrrole (0.5g). At the end
of the reaction and after cooling, the precipitated product was filtered and washed with cold
ethanol, and finally dried in vacuum.
The product appearance: yellow solid; yield: 68.13%; m =121.31°C (determined by DSC).
p
-1
FTIR (ATR) ν (cm ): 3060 (aromatic C-H stretch), 1625 (C=N), 1587, 1503, 1466 and 1437
(aromatic C-C stretch), 1335 (C-N stretch), 726 (C-H out of plane).
1
9
H-NMR (300 MHz, acetone-D ) δ (ppm): 8.72 (s, 1H, H , HC=N), 8.52 (dt, J=8.6, 1Hz,
6
1
4
12
4
1
H, H aromatic), 8.28 (dd, J=8.2, 1.4Hz, 1H, H aromatic), 8.14 (dd, J=8.2, 1.2Hz, 1H, H
2
5,7
11
aromatic), 7.92 (m, 4H, 2C-H pyrrole, H aromatic), 7.54 (m, 1H, H aromatic), 7.44 (m,
2
13
6
3
H, 2C-H pyrrole, H aromatic), 6.89 (dd, J=8.4, 2.8Hz, 1H, H aromatic).
1
3
9
10
14
C-NMR (75 MHz, acetone-D ) δ (ppm): 162.89(C , C=N), 150.62(C ), 137.52(C ),
6
1
2
8
5
6
13
11
4
1
1
28.18(C ), 128.12(C ), 126.36(C ), 125.83(C ), 124.40(C ), 123.32(C ), 122.24(C ),
7
1
2
22.19(C ), 120.67(C , pyrrole), 109.75(C , pyrrole).
+
+
+
+
MS (ES ): 247 (M ), 245.277 (C H N O , base peak). Accurate mass (ES ): 247.206,
1
6
11
2
calculated: 247.111.
2
.3.6 Synthesis of monomer M5: N-(pyridin-2-yl-methylene)-3-(pyrrol-1-yl)-propan-1-amine
The monomer M5 was prepared in the same manner as M1, with 8mmol (0.86g) of 2-
pyridinecarboxylaldehyde and an equivalent of 1-(2-aminopropyl) pyrrole (1g). At the end of
the reaction the product was purified by column chromatography using a mixture of hexane-
ethylacetate (4:1) as an eluent revealing high purity of the compound.
The product appearance: garnet viscous oil; yield: 91.76%.
1
2

ACCEPTED MANUSCRIPT
-1
FTIR (ATR) ν (cm ): 3094, 3056 (aromatic C-H stretch), 2931 and 2858 (aliphatic C-H
stretch), 1647 (C=N), 1591, 1515 and 1428 (aromatic C-C stretch), 1283 (C-N stretch), 760,
7
20 (C-H out of plane).
1
11
H-NMR (300 MHz, acetone-D ) δ (ppm): 8.63 (d, J= 6.38Hz,1H, H , aromatic), 8.36 (s,
6
6
8
9
1
7
H, H , HC=N), 8.03 (d, J=6.86Hz, 1H, H , aromatic), 7.93 (t, J=7.70Hz, 1H, H , aromatic),
1
0
1
2
.50 (m, 1H, H , aromatic), 6.72 (t, J=2.1Hz, 2H, C-H pyrrole), 6.5 (t, J=2.1Hz, 2H, C-H
3
5
4
pyrrole), 4.05 (t, J=6.81Hz, 2H , CH ), 3.63 (t, J=6.74Hz, 2H , CH ), 2.19 (p, J=6.76Hz, 2H ,
2
2
CH2).
1
3
7
11
10
C-NMR (75 MHz, acetone-D ) δ (ppm): 162.64(C , C=N), 149.02(C ), 136.72(C ),
6
8
9
6
1
1
1
24.81(C ), 122.68(C ), all aromatic carbons, 149.53(C , C=N), 120.56(C , pyrrole),
2
3
5
4
08.08(C , pyrrole), and 57.90(C ), 48.98(C ), 32.36(C ) aliphatic CH carbons.
2
+
+
+
+
MS (ES ): 213 (M ), 119.144 (C H N , base peak). Accurate mass (ES ): 213.273,
7
7
2
calculated: 213.278.
2
.3.7 Synthesis of monomer M6: 2-(3-pyrrol-1-yl-propylimino-methyl)-quinolin-8-ol
The monomer M6 was prepared in the same manner as M1, with 1.44mmol (0.25g) of 8-
Hydroxy-2-quinoline-carboxaldehyde and an equivalent of 1-(2-aminopropyl) pyrrole
(0.18g). At the end of the reaction and after cooling, the precipitated product was filtered and
washed with cold ethanol, and finally dried in vacuum.
The product appearance: yellow- orange solid; yield: 80.04 %; m =62.45°C (determined by
p
DSC).
-1
FTIR (ATR) ν (cm ): 3379 (OH aromatic), 3097, 3050 (aromatic C-H stretch), 2923 and
847 (aliphatic C-H stretch), 1645 (C=N), 1564, 1493 and 1450 (aromatic C-C stretch), 1280
C-N stretch), 1240 (=C-OH phenolic), 8.35, 720 (C-H out of plane).
2
(
1
3

ACCEPTED MANUSCRIPT
1
6
H-NMR (300 MHz, acetone-D ) δ (ppm): 8.40 (s, 1H, H , HC=N), 8.27 (d, J=8.40Hz, 1H,
6
9
8
11
H , aromatic), 8.11 (d, J=8.60Hz, 1H, H , aromatic), 7.43(d, J=7.50Hz, 1H, H , aromatic),
1
2
13
7
6
.37 (dd, J=8.20, 1.40Hz, 1H, H , aromatic), 7.08 (dd, J=7.50, 1.40Hz, 1H, H , aromatic),
1
2
3
.66 (t, J=2.10Hz , 2H, C-H pyrrole), 5.91 (m, 2H, C-H pyrrole), 4.01 (t, J=6.90Hz, 2H ,
5
4
CH ), 3.59 (t, J=6.70Hz, 2H , CH ), 2.10(p, J=6.70Hz, 2H , CH ).
2
2
2
1
3
7
14
15
C-NMR (75 MHz, acetone-D ) δ (ppm): 162.94(C , C=N), 152.08(C ), 137.54(C ),
6
9
10
12
13
6
1
1
33.27(C ), 130.98(C ), 129.67(C ), 119.53(C ), all aromatic carbons, 154.38(C , C=N),
1
2
3
5
4
21.23(C , pyrrole), 108.31(C , pyrrole), and 58.66(C ), 47.64(C ), 33.57(C ) aliphatic CH
2
carbons.
+
+
+
+
MS (ES ): 279 (M ), 107.243(C H N , base peak). Accurate mass (ES ): 279.248, calculated:
7
9
2
79.336.
2
.3.8 Synthesis of monomer M7: 2-(3-pyrrol-1-yl-phenylimino-methyl)-quinolin-8-ol
The monomer M7 was prepared in the same manner as M1, with 1.44mmol (0.25g) of 8-
Hydroxy-2-quinoline-carboxaldehyde and an equivalent of 1-(2-aminophenyl) pyrrole
(0.23g). At the end of the reaction and after cooling, the precipitated product was filtered and
washed with cold ethanol, and finally dried in vacuum.
The product appearance: dark red solid: yield: 84.44%; m =167.23°C (determined by DSC).
p
-1
FTIR (ATR) ν (cm ): 3360 (OH aromatic), 3100, 3055 (aromatic C-H stretch), 1616 (C=N),
1
580, 1507 and 1480 (aromatic C-C stretch), 1320 (C-N stretch), 1245 (=C-OH phenolic),
8
35, 737 (C-H out of plane).
1
11
H-NMR (300 MHz, acetone-D ) δ(ppm): 8.63 (s, 1H, H , HC=N), 8.25 (d, J=8.57Hz, 1H,
6
H , aromatic), 7.50-7.36 (m, 5H, H , H , H H7,9 aromatic), 7.13 (dd, J=7.44, 1.37Hz, 1H,
1
4
16
6
13
,
1
7
18
4
8
H , aromatic), 6.99 (m, 2H, H , H aromatic), 6.78 (m, 1H, H , aromatic), 6.40 (broad, s,
py
1
4

ACCEPTED MANUSCRIPT
1
9
4
2
1
H, OH ), 6.31 (t, J=3.22Hz, 1H, C-H pyrrole), 6.07 (d, J=2.54Hz, 1H, C-H pyrrole), 5.93
3
(
d, J=2.86Hz, 1H, C-H pyrrole).
1
3
19
12
20
C-NMR (75 MHz, acetone-D ) δ(ppm): 175.36(C ), 160.39(C ), 137.70(C ),
6
1
4
10
5
9
17
15
7
1
1
1
36.53(C ), 134.43(C ), 131.28(C ), 128.55(C ), 127.67(C ), 125.29(C ), 124.81(C ),
8
13
16
5
11
23.91(C ), 121.51(C ), 118.37(C ), 115.36(C ), all aromatic carbons, 159.03(C , C=N),
1
,4
2,3
19.70(C , pyrrole), 110.87(C , pyrrole).
+
+
+
+
MS (ES ): 311 (M ), 311.112 (C H N O , base peak). Accurate mass (ES ): 311.112,
2
0
15
3
calculated: 311.12.
3
. Results and discussion
.1 Characterisation of 1-(3-aminopropyl) pyrrole (APP)
3
For the synthesis of the starting material 1-(3-aminopropyl)-pyrrole (APP), a catalytic
reduction reaction was applied using LiAlH on N-(2-cyanoethyl) pyrrole (NCPy) (Fig. 1).
4
This regioselective method leads to a conversion of the nitrile to the amine group, and the
final product can be obtained in good yield and purity.
Fig. 4 represents the FT-IR spectra of NCPy and the obtained product. It can be noticed that
-1
the absorption band of the nitrile group (CN) at 2250cm completely disappeared, and that
the absorption of the amine band appeared with two weak bands (N-H deformation out of
-1
-1
plane) at 3369-3292cm and 1503cm , respectively, confirming the formation of APP (Fig.
4
). These results were supported by H. Qin et al. [5] who recorded the same absorption bands
for APP in relationship with the reduction of the nitrile group and the appearance of the amine
group.
1
5

ACCEPTED MANUSCRIPT
Fig. 4. FT-IR spectra of raw product NCPy and APP with monomers M1, M3, and M5.
1
These observations were confirmed by H-NMR spectroscopy (Fig. 5a), where new peaks
were found in the spectrum of the product compared to NCPy: the amine function NH2
6
5
(
singlet, H ) at 1.22ppm, and a third methylene peak NCH at 2.60ppm (triplet, H ). These
2
results were found to be in good agreement with literature data for the same product [25-27].
In particular, the peak corresponding to the amine function NH usually appears above
2
2
2
.5ppm, but since APP represents a primary aliphatic amine, the peak was recorded far below
1
3
ppm. The structure of APP was also confirmed by C-NMR analysis (Fig. 5b), with the
5
appearance of methylene carbon attached to the amine function at 39.07ppm (C ). Another
confirmation of these results was obtained from GC-MS spectra exhibiting a molecule peak
corresponding to a mass of 124.145g/mol, which is in good agreement with the calculated
mass (124.184g/mol).
1
6

ACCEPTED MANUSCRIPT
1
13
Fig. 5. (a): H-NMR and (b): C-NMR of 1-(2-aminophenyl) pyrrole (APP) in CDCl .
3
1
7

ACCEPTED MANUSCRIPT
3
.2 Characterisation of the monomers M1-M7
In the second part of this work, two series of functional Schiff base monomers were
synthesized; the first one consists of N-alkyl pyrrole derivatives (M1, M5, and M6)
possessing an aliphatic chain, synthesized from APP, and the second series are derivatives of
N-phenyl pyrrole (M2, M3, M4, and M7), prepared from 1-(2-aminophenyl) pyrrole.
Moreover, these molecules contain coordination sites in their structures such as the
azomethine group (C=N), and electron pairs of heteroatoms like oxygen and nitrogen. It
should be highlighted that these compounds were obtained by simple condensation reactions
between amines and suitable aldehydes, in good yield, as described in [24].
It was found that the monomers of the first series are viscous at room temperature, or present
low melting points e.g. for M6: m =62.45°C, in contrast to those of the second series which
p
exhibit much higher melting temperatures. The physicochemical properties of these
compounds depend strongly on the nature of the amine, presenting either a propyl group with
APP, or being a phenyl pyrrole derivative.
3
.2.1 FT-IR spectroscopical characterisation
Fig. 4 illustrates the FT-IR spectra of all synthesized compounds. As expected, these spectra
reveal the presence of several common bands of these structures. In particular, the imine or
-1
-1
azomethine function (C=N) was detected between 1600 and 1650cm : M1 (cm ): 1630, M2
-1
-1
-1
-1
-1
(
cm ): 1610, M3 (cm ): 1625, M4 (cm ): 1625, M5 (cm ): 1647, M6 (cm ): 1648, M7
-1
(
cm ): 1616). The appearance of this band confirms that these structures represent Schiff
bases following the outcome of literature reports [28, 29], approving thus occurrence of
condensation reactions between amines and aldehydes. Furthermore, it was found that Pyrrole
is present in all structures through its characteristic bands: ν CH (aromatic stretching) at 3100
1
8

ACCEPTED MANUSCRIPT
-1
-1
and 3090cm , confirmed by either ν C=C (stretching), and ν CN between 1380 and 1300cm ,
-1
or by δ CH (deformation out of plane) around 720-740cm [17]. It should be mentioned that
some other functional groups such as ν C=C (aromatic) and ν OH (phenolic) were observed
-1
between 3500 and 3300cm , in addition to absorption bands of C-O (phenolic) situated
-1
between 1270 and 1220 cm , which were present in all structures except M4 and M5 [30].
Nevertheless, there are some differences related to the nature of the amine which was used,
for example monomers from the first series (M1, M5, M6) present asymmetric and symmetric
-1
-1
stretching of the methylene group at 2970cm and 2850cm , respectively, which can be
attributed to the presence of the propyl group (see Fig. 1) [17].
In the case of monomers of the second series (M2, M3, M4, M7), strong aromatic signals
were observed in the structural analysis, due to the presence of phenyl moieties and the
introduction of aromatic aldehydes during the synthesis. As a consequence, one can notice the
presence of aromatic C-H stretching while the out plane bending for the aromatic skeleton can
-1
be seen between 720 and 850cm [31].
1
3
.2.2 Characterisation by H-NMR analysis
1
Additionally, the synthesized compounds were characterized by H-NMR spectroscopy
confirming the various observations made by FTIR, and bringing more details on the structure
1
of the different monomers. Quantitative analyses of H-NMR spectra in terms of the
integration of each resonance, in relationship with the corresponding number of protons, show
1
a good agreement with the proposed structures. Details about the analysis of the H-NMR
spectra were given in the previous section (experimental section). Since these spectra present
some similarities, proton spectra from M1, M2, and M5 will be discussed as selected
examples (Fig. 6).
1
9

ACCEPTED MANUSCRIPT
1
Fig. 6. H-NMR spectra of monomers (a): M1, (b): M2, and (c): M5.
The condensation reaction previously expressed by the presence of imine groups is
represented by the presence of the methine proton (HC=N). This proton was observed for all
prepared monomers as singlet (one integrated proton): M1 (ppm): 8.89, M2 (ppm): 8.73, M3
(ppm): 9.76, M4 (ppm): 8.72, M5 (ppm): 8.25, M6 (ppm): 8.40, M7 (ppm): 8.63. The
singularity of this peak has been reported by different authors [24, 28, 32].
1H-NMR data also confirm the presence of the pyrrole moiety by the shift of pyrrolic CH- in
all structures, showing characteristic peaks for α- and β-protons in two positions: the α-proton
1
is more shifted than the β-proton, for example, M1: 6.75 (s, 2H , C-H at α N-pyrrole), 6.12 (s,
2
2
2
2
H , C-H at β N-pyrrole); M3: 7.19-6.99 (m, 2H, 2C-H at α N-pyrrole), 6.56 (m, 2H, C-H at
β N-pyrrole 2H) [10,33].
The presence of the propyl group in the structure of the synthesized azomethine monomers
1
(
M1, M5, and M6) could be confirmed by H-NMR spectroscopy as well. Indeed, aliphatic
2
0

ACCEPTED MANUSCRIPT
protons (CH ) present two triplets in three positions, and a pentaplet. Integration of the signals
2
3
5
yielded two protons in each case; M1 (ppm): 4.09 (t, J=6.70Hz, 2H ), 3.60 (t, J=6.77Hz, 2H ),
4
3
5
2
.24 (p, J=6.76Hz, 2H ); M5 (ppm): 3.97 (t, J=6.80Hz, 2H ), 3.60 (t, J=6.70Hz, 2H ), 2.24 (p,
4
3
5
J=6.76Hz, 2H ); M6 (ppm): 4.01 (t, J=6.90Hz, 2H ), 3.59 (t, J=6.70Hz, 2H ), 2.10 (p,
4
J=6.70Hz, 2H ) [19].
1H-NMR analysis allowed also to identify the aromatic protons of the monomeric structures
(experimental section). The hydroxyl (OH) proton belonging to the phenol group of the
1
monomers of the second series was observed by H-NMR analysis for M1 (ppm): 10.89 (s,
1
6
15
19
1
H, OH ); M2 (ppm): 5.88 (s, 1H, OH ); M3 (ppm): 5.28 (s, 1H, C-OH ); M7 (ppm): 6.40
1
9
(
s, 1H, OH ) [34, 35].
1
3
3
.2.3 Characterisation by C-NMR analysis
1
13
In addition to the H-NMR analysis presented before, Fig. 7 shows C-NMR spectra of the
1
3
monomers M1, M2, and M5. The results from C-NMR spectroscopy confirm the presence
of the carbon imine group (C=N) for all monomers: M1 (ppm): 160.66, M2 (ppm): 161.29,
M3 (ppm): 157.68, M4 (ppm): 162.89, M5 (ppm): 162.64, M6 (ppm):162.94, M7 (ppm):
1
59.03ppm [32]. Moreover, spectral analysis allows to distinguish between aromatic C=N and
9
10
6
vinylic CH=N: M4 (ppm):162.89 (C , C=N), 150.62 (C ), M5 (ppm): 149.53 (C , C=N),
7
6
7
11
1
62.64 (C , C=N), M6 (ppm): 154.38 (C , C=N), 162.94 (C , C=N), M7 (ppm): 159.03 (C ,
1
2
13
C=N), 160.39(C ). It should be mentioned that the C peaks of the azomethine group are
generally more deshielded than those corresponding to the aromatic (C=N) function [29, 36].
2
1

ACCEPTED MANUSCRIPT
1
3
Fig. 7. C-NMR spectra of monomers (a): M1, (b): M2, and (c): M5.
The presence of phenolic OH-groups in the structures of monomers M1-M3, M6, and M7 was
confirmed by the presence of signals of carbons bonded to phenolic -OH: M1-M3 (ppm)
1
80.60 (C16), 178.58 (C15), 140.16 (C19); M6 and M7 (ppm) 152.08(C14), 175.36(C19).
Methylene (CH ) signals from the propyl group are present in the spectra of monomers of the
2
3
5
4
first series (M1, M5, M6): CH , M1 (ppm) 58.27(C ), 47.14(C ), 33.13(C ), M5 (ppm)
2
3
5
4
3
5
4
5
7.90(C ), 48.98(C ), 32.36(C ), M6 (ppm) 58.66(C ), 47.64(C ), 33.57(C ) [37].
3
.2.4 Characterisation by GC-MS
The GC-MS analysis allowed to complete and to confirm the structure of the synthesized
products. The purity of the monomers was verified by GC, and MS yields accurate masses.
The corresponding results were reported in the experimental part. As an example, Fig. 8
represents the GC chromatogram and MS spectrum of the monomer M2 exhibiting a single
2
2

ACCEPTED MANUSCRIPT
peak at 40.4min (GC) and a mass of 262.298g/mol, which corresponds to the exact molar
weight of this monomer.
Fig. 8. Gas chromatogram (GC) and mass spectrum (MS) (inset) of monomer M2
4
. Conclusion
The synthesis of seven new Schiff base monomers was presented in this work. In particular,
two series of pyrrole derivatives were successfully obtained in high purity and yield. The first
series consists of N-propyl pyrrole compounds (M1, M5, M6), and the second series include
N-phenyl pyrrole based molecules (M2, M3, M4, M7). These monomers were obtained by
simple condensation reactions, and the structures proposed in the experimental section were
found to agree well with the results obtained by different spectroscopic analysis methods like
1
13
FT-IR, H-NMR, C-NMR and GC-MS.
The presence of groups such as azomethine (C=N), hydroxyl (OH) or heteroatoms like
nitrogen and oxygen as electron donor in these compounds, makes them good future
2
3

ACCEPTED MANUSCRIPT
candidates able to coordinate with various metal ions. Monomers containing the pyrrole
moiety are likely to be electro-attractive and can be considered as interesting starting
materials for electrochemical polymerization reactions. These monomers present thus
promising applications in various fields like electrical, optical, molecular recognition or to
elaborate modified electrodes (ME), which can be applied in catalysis.
Acknowledgements
This work has been accomplished in the framework of an international research program. The
authors gratefully acknowledge the support of the Algerian Ministry of Higher Education and
Scientific Research, the University USTOMB of Oran/Algeria, the CNRS, and the University
of Lille 1 – Sciences and Technologies/France.
2
4

ACCEPTED MANUSCRIPT
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(
2
9