J. Chil. Chem. Soc., 60, Nº 3 (2015)
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1529 cm-1, NO2-, at 1489 cm-1 and at 1430 cm-1, C-O at 1206 cm-1, vinyl bond
at 1623 cm-1. 1H-NMR (DMSO-d6): aromatic CH at 8.12 ppm (1H,d); CH at
7.63 ppm (1H,d); vinyl CH at 7.75 ppm (1H,d), vinyl CH at 6.60 ppm (1H,d);
-OH at 12.70 ppm. Elemental analysis, Calcd.: C 42.2, H 2.5, N 7.0, S 16.10.
Found: C 41.0, H 1.6, N 6.0, S 12.13.
1249 cm-1, vinyl bond at 1598 cm-1. H-NMR (DMSO-d6): CH phenylen at
5.48 ppm (2H,d); CH phenylen at 6.53 ppm (2H,d); CH vinyl at 6.14 ppm, NH2
at 3.64 ppm, CH=N + CH vinyl + CH thiophene at 7.23 ppm (4H, m).
Synthesis of polymers
Polyamides were synthesized under the same experimental condition
using the phosphorylation method. Triphenylphosphite was used as
3-(5-aminothiophen-2-yl)propenoic acid, (ATPA): In a 50 mL round-
bottom flask, equipped with a reflux condenser 0.83 g (4.16 mmole)
3-(5-nitrothiophen-2-yl)propenoic acid, 27 mL acetic acid, 1.1 mL water, six
drops 37% HCl were placed and the mixture was heated to 95-100 ºC. Once
dissolved (10 min), 0.60 g tin was added and after 20 min 0.28 g tin and 5
drops HCl (37 %) were added. The reaction mixture was refluxed for 2 h after
which the hot mixture was filtered, concentrated to half its volume followed by
volume duplication with water. The mixture was left standing for 48 h and then
vacuum-filtered, washed with a small amount of water and finally dried at 60
ºC. 0.30 g of product was obtained, 42.5 % yield. mp > at 300º C. FT-IR: NH
+ OH, at 3700-3000 cm-1, C=O, at 1688 cm-1, C-O at 1206 cm-1, vinyl bond at
1618 cm-1. 1H-NMR (DMSO-d6): aromatic CH at 8.10 ppm (1H,d); CH at 7.60
ppm (1H,d); vinyl CH at 7.75 ppm (1H,d), vinyl CH at 6.58 ppm (1H,d); -OH
at 12.6 ppm, NH2 at 2.50 ppm.
initiator and polymers can be produced with higher molecular weight33
.
3-(5-aminothiophen-2-yl)propenoic acid polymerization was accomplished as
follow: to a 20 mL round-bottom flask equipped with a reflux condenser 1.54
mmol monomer, 0.72 mL DMF, 0.72 mL pyridine, 0.44 g triphenylphosphite
and catalytic amounts of LiCl were added. The mixture was heated to 110-120
ºC for 17 h, concentrated to half its volume, cooled to room temperature, 10
mL water added and stirred. After being left standing for 10 min, the solid
was filtrated off and successively washed with a small amount of 3 M HCl,
water, and methanol. The polymer was dried at 60 ºC in an oven, and 0.24 g
was obtained.
3-(5-aminofuran-2-yl) propenoic acid polymerization was performed
using 1.1 mL DMF, 1.1 mL pyridine, 0.44 g triphenylphosphite, and for
3-(4-((5-aminothiophen-2-yl) methyleneamino)phenyl) propenoic acid
polymerization 12.9 mL DMF, 4.8 mL pyridine and 0.97 g initiator were
utilized. 0.22 and 0.071 g of the respective polymer was obtained.
In the present work, polyamides obtained from 3-(5-aminothiophene-2-
yl)propenoic acid and 3-(5-aminofuran-2-yl)propenoic acid were called PTPA
and PFPA respectively. Monomers of those polymers are designated ATPA and
AFPA respectively. Polyamide synthesized from 3-(4-((5-aminothiophen-2-
yl)methyleneamino) phenyl)propenoic acid is called PTIPA and its respective
monomer ATIPA.
3-(5-nitrofuran-2-yl) propenoic acid: In a 50 mL round-bottom flask,
equipped with a reflux condenser 3.0 g (17 mmole) 5-nitrofuraldehyde, 2.46
g (24 mmole) malonic acid and 1.86 g (24 mmole) pyridine were placed. The
mixture was heated to 150 ºC, cooled to room temperature, next, the solid was
extracted two times using 20 mL ethanol to boiling and then, again extracted
the solid with ethanol to boiling that contain 20 drops pyridine, the extraction
process of the solid using a mix ethanol-pyridine was repeated five times,
then all the extracts were boiled and filtered. The filtrates were gathered and
concentrated to half its volume by solvent evaporation. The mixture volume
was duplicated by adding water, and finally acidified with HCl (37%) to pH
0-2 under stirring. The obtained mixture was left standing for 2 h and then
filtered. The solid product was dried at 60 ºC in an oven. 1.20 g of product was
obtained (30.0 % yield), mp = 158-160 ºC (decomposed). FT-IR: OH, at 2906
cm-1 (broad), C=O, at 1678 cm-1, C=C, at 1573 cm-1, C-O at 1201 cm-1, vinyl
RESULTS AND DISCUSSION
Figure 1 depicts monomers synthesis scheme. 3-(5-nitrothiophene-2-
yl)propenoic acid, 3-(5-nitrofuran-2-yl)propenoic acid, were obtained by
condensation of malonic acid with 5-nitrothiophene-2-carboxaldehyde and
5-nitrofuraldehyde in the presence of pyridine. Selective reduction of the
nitro compounds in the presence of vinyl bonds was accomplished using
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bond at 1623 cm-1. H-NMR (DMSO-d6): aromatic CH at 7.76 ppm (1H,d);
CH at 7.28 ppm (1H,d); vinyl CH at 7.46 ppm (1H,d), vinyl CH at 6.51 ppm
(1H,d); -OH at 12.88 ppm (1H,s). Elemental analysis, Calcd.: C 45.9, H 2.8, N
7.6, O 43.7. Found: C 44.8, H 2.4, N 6.6, O 46.2.
a
Sn/AcOH/HCl mixture. 3-(4-((5-nitrothiophen-2-yl)methyleneamino)
phenyl) propenoic reduction was performed using a Zn/NH Cl/H2O mixture.
3-(5-aminofuran-2-yl)propenoic acid, (AFPA):A 20 mL round-bottom
flask, equipped with a reflux condenser it was charged with 0.45 g (2.5 mmole)
3-(5-nitrofuran-2-yl)propenoic acid, 8 mL acetic acid, 0.6 mL water and 3
drops 37% HCl and the mixture was heated and once solubilized, 0.30 g tin was
added and refluxed under stirring during 100 min. The hot mixture was filtered
and the filtrate was concentrated to half its volume by evaporation, cooled to
room temperature, its volume duplicated with water, left standing, and finally
filtrated and dried at 60 ºC in an oven. 0.14 g was obtained. (33.2 % yield), mp
>300 ºC. FT-IR: OH, at 3423 cm-1, C=O, at 1718 cm-1, C=C, at 1655 cm-1, C-O
at 1231 cm-1, vinyl bond at 1589 cm-1. 1H-NMR (DMSO): aromatic CH at 7.0
ppm (1H,d); CH at 6.9 ppm (1H,d); vinyl CH at 7.2 ppm (1H,d), vinyl CH at
6.5 ppm (1H,d); NH2 at 3.6 ppm.
Sn/AcOH/HCl mixture hidrolyzes the imine group and wa4s thus discarded.
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Selective reduction of each nitro group was confirmed by H-NMR and FT-
IR spectroscopy. H-NMR exhibited vinyl hydrogen signals with a coupling
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constant of 17 Hz 34
.
3-(4-(((5-nitrothiophen-2-yl)methylene)amino)phenyl)propenoic
acid:
In a 100 mL round-bottomed flask, equipped with a reflux condenser, were
added 0.63 g (4.1 mmol) 5-nitro-2-thiophene-2-carboxaldehyde dissolved in
20 mL of heated ethanol, 0.80 g (4.0 mmole) 3-(p-aminophenyl)propenoic acid
hydrochloride dissolved in 40 mL hot ethanol, the mixture was heated during 1
h under stirring, then, it was immediately vacuum filtered. The solid was then
washed with ethanol and dried at 60 ºC. 0.17 g product was obtained (yield
14.1 %). mp = 276 ºC (decomposed). FT-IR: OH, at 2816 cm-1 (broad), C=O,
at 1678 cm-1, NO2-, at 1489 cm-1 and 1420 cm-1, C-O at 1211 cm-1, vinyl bond at
1618 cm-1. 1H-NMR (DMSO-d6): CH thiophene ring at 8.20 ppm (1H,d); CH
thiophene ring at 7.75 ppm (1H,d); CH=N at 8.95 ppm (1H; s); CH phenylene
at 7.78 ppm (2H, d), CH phenylene at 7.39 ppm (2H,d), vinyl CH at 7.61 ppm
(1H,d), vinyl CH at 6.56 ppm (1H,d); -OH at 12.5 ppm (1H,s).
3-(4-(((5-aminothiophen-2-yl)methylene)amino)phenyl)propenoic acid,
(ATIPA):
Fig. 1: Synthesis of a) ATPA, b) AFPA, c) ATIPA monomers
1.0 g nitro-compound (3.3 mmol), 25 mL de methanol, 2.8 mL of water,
0.52 g NH4Cl 50 mL were placed in a round-bottom flask equipped with a
reflux condenser. The stirred mixture was heated for 10 min after which 3.5
g of Zn powder was slowly added. The mixture was now heated during 105
min at 71 ºC, and the hot mixture vacuum filtered, concentrated to half its
volume, cooled in a water bath for 15 min or until separation of a solid occurs.
The mixture was filtered, washed with ebulled methanol and dried at 60 ºC in
an oven. 0.17 g amino compound was obtained (18.9 % yield), mp = 255 ºC
(decomposed). FT-IR: OH, at 3219, cm-1 (broad), C=O, at 1633 cm-1, C-O at
Polyamides FT-IR spectra are shown in Fig. 2. PTPA, PFPA and PTIPA
show characteristic absorption bands at 3200 cm-1 (NH+OH); 1684, 1713,
1657 cm-1 (C=O); 1594, 1593, 1588 cm-1 (vinyl bond); 1483, 1490, 1487 cm-1
(aromatic CH=CH). The characteristic bands of carbonyl and NH group in all
spectra confirm the presence of amide groups.
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