Bifunctional acyl-1,2,4-triazole: An alternative monomer of dicarbonyl chloride for metal-and halogen-free polyester synthesis

Article abstract of DOI:10.1246/cl.171098

Bifunctional acyl-bis(1,2,4-triazole) functioned as a highly reactive and nontoxic, halogen-free monomer for polyester synthesis that did not require a metal catalyst. Isophthaloyl 1,2,4-triazole was prepared from the corresponding chloride and polymerized with 1,12-dodecanediol at 120 °C in the presence of 4-(N,N-dimethylamino)pyridine, resulting in polyester with high molecular weight (Mn = 48.3

Full text of DOI:10.1246/cl.171098

Received: November 22, 2017 | Accepted: November 28, 2017 | Web Released: December 8, 2017
CL-171098
Bifunctional Acyl-1,2,4-triazole: An Alternative Monomer of Dicarbonyl Chloride
for Metal- and Halogen-free Polyester Synthesis
Yasuhiro Kohsaka,*1 Kazumasa Homma,1 Ichiro Mori,1 Susumu Sugiyama,2 and Yoshikazu Kimura2
1Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
2Iharanikkei Chemical Industry Co., Ltd., 5700-1 Kambara, Shimizu-ku, Shizuoka, Shizuoka 421-3203, Japan
E-mail: kohsaka@shinshu-u.ac.jp
Bifunctional acyl-bis(1,2,4-triazole) functioned as a highly
reactive and nontoxic, halogen-free monomer for polyester
synthesis that did not require a metal catalyst. Isophthaloyl
1,2,4-triazole was prepared from the corresponding chloride and
polymerized with 1,12-dodecanediol at 120 °C in the presence
of 4-(N,N-dimethylamino)pyridine, resulting in polyester with
high molecular weight (Mn = 48.3 © 103) as a colorless solid.
The use of solvents such as diphenyl ether was effective to
conduct the polymerization of monomers that would not melt at
low temperature.
Recently, we have found that acylazole, an active amide
prepared from acyl chloride and 1,2,4-triazole, quantitatively
yields esters at comparable and higher reaction rate than acyl
chloride in the presence of 4-(N,N-dimethylamino)pyridine
(DMAP) and 4-pyrrolydinopyridine (PPY), respectively, under
ambient conditions.17 Consequently, we envisioned that bifunc-
tional acyl-1,2,4-triazoles might function as an alternative
monomer of dicarbonyl chlorides. On the other hand, however,
it is not always true that the best conditions and procedures for
organic synthesis are best for polymerization; side reactions such
as cyclization14 and transesterification (“back-biting”)1,18 exist
behind the propagation that prevent the increase of molecular
weight. In addition, the solubility of polyester restricts the
applicable solvents, while the high viscosity decreases the
reaction rate. In fact, we have found that the melt polymerization
of bifunctional acyl-1,2,4-triazole afforded better results than
solution polymerization conducted in a similar manner to the
organic reactions described in our latest report.17 In this report,
we describe the polymerization of bifunctional acyl-1,2,4-
triazoles through various methods and conditions and conclude
that the new monomers provide polyester synthesis under mild
conditions without metal catalyst and halogen atoms.
In our first experiments, the isophthaloyl group was chosen
as a backbone, as the polyesters were reported as soluble in
tetrahydrofuran (THF) and chloroform and thus convenient for
characterization.14 In addition, the meta-substitution excludes
the reactivity change from the substituent effects simplifying the
discussion. Isophthaloyl bis(1,2,4-triazole) (1b)19,20 and diimi-
dazole (1c)21 were prepared from the substitution reaction of
isophthaloyl dichloride (1a) with 1,2,4-triazole and imidazole,
respectively, in almost quantitative yields (Scheme 1). The
obtained crystals were stable enough to be stored in a
refrigerator for more than one year.
Keywords: Polyester synthesis
| Metal- and halogen free |
Acyl-1,2,4-triazole
Polyesters are useful plastic materials with excellent me-
chanical, thermal, and optical properties. A typical procedure to
prepare polyesters is the direct esterification of dicarboxylic acid
or the transesterification of their esters with diols. For example,
poly(ethylene terephthalate) (PET) is industrially synthesized by
the transesterification of dimethyl terephthalate and ethylene
glycol in two-step stages.1 However, both direct esterification
and transesterification require high temperature, 250 °C or above,
and metal catalysts in order to enhance the reaction rate and to
achieve high molecular weight.2-7 In addition, as the reactions
are equilibrium processes, the removal of liberated water/diols
under partial or high vacuum are necessary. Recently, these harsh
conditions have become problems not only for the considerable
expenditure of energy but also for other specific reasons. For
example, residual heavy metals from the catalysts become issues
for use in food applications and environmental pollution from
the plastic waste,8 while they might deteriorate the performances
of electric devices. Therefore, new catalytic systems utilizing
nontoxic metals6-9 and organic molecules10 for polyester
syntheses have been of interest. In other words, synthetic
methods for polyester with high molecular weight under mild
conditions8-13 without heavy metal catalyst are desirable.10
As is well-known, dicarbonyl chlorides have high reactivity,
and the polycondensation with diol can be employed in mild
conditions even in the absence of catalyst.14,15 These features
seem better than the aforementioned direct esterification/trans-
esterification processes, but the industrial use of the monomer
has still been limited due to the liberated acidic gas, hydrogen
chloride, which causes problems such as toxicity and corrosion
of metal reactors. In addition, the residual hydrogen chloride
might promote the degradation of the resulting polymer by
hydrolysis and would not be favored for electric devices. An
active ester prepared in situ from dicarboxylic acid and
carbodiimide is a possible alternative method to achieve the
polymerization under ambient conditions,16 but the high cost of
condensation agent remains a significant issue.
We have recently reported that the esterification of benzoyl
azoles with primary alcohol did not proceed in CH2Cl2 at
ambient temperature but were efficiently catalyzed with DMAP
and PPY.17 In particular, benzoyl 1,2,4-triazole esterified at a
fast rate comparable to benzoyl chloride, while the rate of
esterification of benzoylimidazole was much slower. Therefore,
the polycondensations of 1b and 1c with 1,4-butanediol (2a)
H
N
O
O
O
O
X
a
c
f
N
Cl
Cl
N
X
N
N
N
b
X
d
e
1a
1b (X = N)
1c (X = CH)
Scheme 1. Synthesis of bifunctional acylazoles.
Chem. Lett. 2018, 47, 221–224 | doi:10.1246/cl.171098
© 2018 The Chemical Society of Japan | 221

Table 2. Polycondensation of isophthaloyl derivatives (1) and
diols (2, 1.02 equiv) in bulk for 3 h in argon atmosphere under
reduced pressure to 375 Torr
O
O
cat. DMAP
1a-c
HO CH2 x OH
O
CH2 x O
n
2a (x = 4)
2b (x = 6)
2c (x = 12)
a
Monomer
Temp. Yield
Mn
Run
Đa Color
/°C
/%
(©103)
1
2
4b
5b
1a
1a
2a
2b
2b
2b
2b
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
180
180
180
180
180
180
180
180
180
150
150
120
120
120
120
>99
81
83
94
61
89
>99
91
>99
>99
>99
>99
83
®
14.6
5.1
8.6
1.9
23.1
21.6
18.6
3.0
31.6
22.6
48.3
15.8
20.2
14.6
®
colorless
Scheme 2. Polycondensation of 1a and the azole derivatives.
1.46 colorless
1.78 brown
1.54 brown
1.29 brown
1.53 colorless
1.60 brown
1.51 brown
1.46 brown
1.84 colorless
1.50 colorless
1.84 colorless
1.46 colorless
1.53 colorless
1.77 colorless
6b,c 1b
7c
8c
1b
1c
1a
1b
1b
1c
1b
1b
1b
1b
1b
1c
Table 1. Polycondensation of isophthaloyl derivatives (1,
6.49 mmol) and 2a (6.49 mmol) in CH2Cl2 (13 mL) at 25 °C
for 24 h
9b
b
10c
11
Yield
/%
Mn
Run
1
Catalysta
Đb
(©103)
12c
13c
14
1
2
3
1a
1b
1c
(Et3N)c
DMAP
DMAP
99
71
81
2.50
1.50
2.00
1.28
1.38
1.16
15c
16
a10 mol %. bDetermined by SEC (40 °C, THF, polystyrene
c
standards). Et3N (2.0 equiv) was used as a proton scavenger.
17d
18d
>99
>99
were conducted under similar conditions, i.e. in CH2Cl2 in the
presence of DMAP (10 mol %) catalyst (Scheme 2, Table 1,
Runs 2 and 3).22 For the control, the polycondensation of 1a was
employed in the presence of Et3N (Run 1). Although all
isophthaloyl monomers underwent polycondensation, the num-
ber-averaged molecular weights (Mns) were less than 104.
Kricheldorf et al. reported that the solution polymerization was
very sensitive to the purity of amine (in the current cases, Et3N
for Run 1 and DMAP for Runs 2 and 3) and molar balance
of monomers,14 while the polymerization often suffers from
competitive cyclization. The low Mns in the above experiments
could be explained with similar reasons.
The sensitivity may not be suitable for discussing the
reactivity differences among the three monomers, 1a-1c, melt
polymerization was conducted (Table 2).23 Although the poly-
merization of 1a and 2a yielded a product insoluble in CHCl3
and THF (Run 4), that of 1a and 1,6-hexanediol (2b) at 180 °C
resulted in a soluble product with high molecular weight
(Mn = 14.6 © 103, Run 5). In a similar manner, 1b was polymer-
ized with 2b in the presence of DMAP (Run 6), resulting in the
polyester but the molecular weight (Mn = 5.1 © 103) was lower
than Run 5. Note that the polymerizations conducted under
reduced pressure (<375 Torr) yielded polymers with higher
molecular weight (Mn = 8.6 © 103, Run 7). Since the esterifica-
tion with 1b is irreversible,24 the effect of vacuum would exist on
the stirring of the reaction mixture by the boiling of liberated
1,2,4-triazole that enhances the diffusion of propagating chains
and/or on the increase of concentration. The details of the effect
of vacuuming will be discussed later. Anyway, the vacuuming
provided better results and thus all the experiments described
below were conducted under reduced pressure unless otherwise
noted. Polymerization of 1c and 2b also yielded the polyester,
although the Mn was low (Run 8).24 It can be explained by
the lower reactivity of acylimidazole than acyl-chloride and
-triazole.17,25 Similar experiments were conducted for 1,12-
dodecanediol (2c, Runs 9-16). In the absence of DMAP
(Run 11), the Mn of the resulting polymer was slightly lower
than that in the polymerized in the presence of DMAP (Run 10),
although both were comparable to that prepared from 1a (Run 9).
aDetermined by SEC (40 °C, THF, polystyrene standards).
bPolymerized in argon atmosphere without vacuum. c10 mol %
of DMAP was added as a catalyst. d10 mol % of PPY was
added as a catalyst.
The imidazole derivative, 1c also afforded the corresponding
polymer in the presence of DMAP, but the Mn was low (Run 12),
similar to Run 8.
It should be noted that the obtained polymers from 1b and
1c were tinged brown, probably due to some oxidized impurities
from 1,2,4-triazole and imidazole. As polyesters are often
applied as transparent plastic materials, the coloration is an issue
to be avoided.18 The polymerizations at lower temperatures,
150 °C (Runs 13 and 14) and 120 °C (Runs 15 and 16), resulted
in colorless polymers. In addition, Mns of the polymers prepared
in the presence of DMAP became higher at lower temperature
(Runs 10, 13, and 15) and particularly, the polymer prepared at
120 °C exhibited the highest (Mn = 48.3 © 103, Run 15) among
them. Therefore, 120 °C is the optimized temperature to obtain
high molecular weight and to suppress the coloration.
It is reported that DMAP catalyzes the transesterification at
high temperature and affords the cyclic oligomer behind the
propagation, which decreases the averaged molecular weight of
polyester.18 In addition, since 2c in excess of 2 mol % against 1b
was employed in the current polymerization according to the
standard conditions for 2a,26 the polymer should have hydroxy
groups at both ends that could increase the transesterification
including cyclization (back-biting). Therefore, a possible reason
why the Mns became lower at higher temperature might be
the formation of such cyclic oligomer by transesterification.
In fact, the transesterification at 180 °C catalyzed by DMAP
was confirmed by model experiments, whereas that at 120 °C
seemed much slower than the propagation (See Supplementary
Information). Furthermore, it was found that the Mns of the
resulting polyesters gradually decreased during the polymeriza-
tion at 180 °C in the presence of DMAP, while Mn increased in
the absence of DMAP (Figure 1a). Therefore, the polymerization
should be conducted at 120 °C and should not employ more than
222 | Chem. Lett. 2018, 47, 221–224 | doi:10.1246/cl.171098
© 2018 The Chemical Society of Japan

30
25
20
15
10
5
3
O
O
(a)
a
b
N
N
N
N
c
d
N
2.5
2
N
O
㾛
3b
cat. DMAP
polyester
㻹
1.5
1
HO CH2 12 OH
2c
0
0
100
200
300
Scheme 3. Polycondensation of 3b and 2c.
㻾㼑㼍㼏㼠㼕㼛㼚㻌㼠㼠㼕㼙㼑㻛㼙㼕㼚
45
3
(b)
Table 3. Polycondensation of 3b and 2c in bulk for 3 h in
40
35
30
25
20
15
10
5
argon atmosphere under reduced pressure to 375 Torr
2.5
2
b
Temp. Yield
Mn
Runa Solvent
Đb Color
/°C
/%
(©103)
㾛
19
®
170
120
120
80
89
71
87
81
40
16.2
17.3
10.9
16.2
6.9
2.16 brown
20
Ph2O
Ph2O
Ph2O
Ph2O
1.75 colorless
1.64 colorless
1.63 colorless
1.63 colorless
㻹
21c
22
1.5
1
23c
80
0
0
100
200
300
400
500
a3b
0.455 mmol,
[3b]0/[2c]0/[DMAP]0 = 1/1.01/0.10,
㻾㼑㼍㼏㼠㼕㼛㼚㻌㼠㼠㼕㼙㼑㻛㼙㼕㼚
Ph2O = 1.5 mL. bDetermined by SEC (40 °C, THF, polystyrene
standards). cPolymerized in argon atmosphere without vacuum.
Figure 1. Time vs. Mn and Đ plots in the polymerizations with
1b and 2b at (a) 180 °C and (b) 120 °C in the presence (red) and
absence (blue) of DMAP catalyst.
170 °C yielded the corresponding polyester (Scheme 3, Table 3,
Run 19), although the color of product was brown. It is known
that the diphenyl ether is effective solvent for polyester synthesis
by transesterification in melt polymerization.28 In a similar
manner, 3b was polymerized with 2c in diphenyl ether. The
reaction mixture at 120 °C was transparent solution and could be
stirred smoothly, resulting in polyester with comparable mo-
lecular weight (Mn = 17.3 © 103, Run 20) to the bulk polymer-
ization (Run 19). Polymerization at 80 °C afforded a similar
result (Run 22). These results indicate that the use of solvents is
very effective to achieve the melt polymerization of bifunctional
acyl-1,2,4-triazole under mild conditions.
It was interesting that the vacuum seemed still effective
to increase the molecular weight (Runs 21 and 23), as the
polymerization without vacuum yielded polyester with lower
molecular weight. In this case, the reaction mixture was
smoothly stirred over the reaction, and thus the effect of vacuum
was not the mixing by boiling. In order to investigate the
possibility of equilibrium, the resulting polymer in Run 22 was
heated again at 80 °C in the presence of DMAP catalyst and an
equimolar amount of 1,2,4-triazole. As the result, molecular
weight increased rather than decreased (before: Mn = 16.2 ©
103, Đ = 1.63; after: Mn = 18.5 © 103, Đ = 1.67). Therefore,
the polymerization is irreversible and does not contain an
equilibrium process. Therefore, the effect of vacuum might
increase the concentration of the reaction system to promote
chain-growth. In fact, the liberated triazole that could perform
as a solvent evaporated and was observed as needlelike crystals
on the head of reactor after applying vacuum.
the required time to suppress transesterification. In order to
optimize the reaction time at 120 °C, the polymerization was
conducted for various periods (Figure 1b). The Mns rapidly grew
up to 70 min. In this period, the propagation in the presence of
DMAP proceeded much faster than that in the absence of the
catalyst. After that, the Mn increased slowly over a long time,
regardless the absence/presence of DMAP. The reaction mixture
became very viscous after 70 min and thus the reaction might be
controlled by diffusion. Since the Mn still increased at 433 min,
the propagation was more favorable than transesterification even
at the later stage of reaction.
Since PPY functions as a more efficient catalyst for the
esterification of acylazoles,17 the polymerizations of 1b (Table 1,
Run 17) and 1c (Run 18) in the presence of PPY were
investigated. Notably, not only 1b but also 1c, which yielded
oligomer in the presence of DMAP (Run 12), afforded the
corresponding polymers. However, the Mns were lower than that
of the polymer prepared from 1b with DMAP catalyst (Run 15).
The results described above suggest that bifunctional acyl-
1,2,4-triazole functions as an alternative monomer to dicarbonyl
chloride for polyester synthesis. However, high temperature for
the melt polymerization still remains as an issue. 1b cannot melt
below 120 °C and thus the temperature was the lowest limit for
melt polymerization in bulk state. This limitation becomes more
serious for the monomers that have melting points at higher
temperature. For example, bifunctional acyl-1,2,4-triazole 3b27
derived from 4,4¤-oxydibenzoyl chloride (3a) has a melting
point at ca. 163 °C, while it is insoluble in melted 2c at 120 °C.
Therefore, the melt polymerization must be conducted above
the melting point of 3b. The polymerization of 3b and 2c at
In conclusion, bifunctional acyl-1,2,4-triazole functioned as
an alternative monomer to dicarbonyl chloride for polyester
synthesis. The monomer yielded colorless polyester with high
Chem. Lett. 2018, 47, 221–224 | doi:10.1246/cl.171098
© 2018 The Chemical Society of Japan | 223

molecular weight (Mn ¯ 48.3 © 103) in the presence of DMAP
catalyst. The use of solvent such as diphenyl ether is effective to
achieve the melt polymerization at mild conditions. Since the
polymerization can be conducted in moderate condition and does
not afford any toxic and acidic biproducts, the procedure might
become facile and practical method in industrial application.
(s, 2H, f), 8.58 (dd, J1 = 8.0 Hz, J2 = 1.8 Hz, 2H, b), 8.15
(s, 2H, e), 7.77 (t, J = 8.0 Hz, 1H, c). 13C NMR (100 MHz,
CDCl3, 26 °C): δ/ppm 163.9, 154.3, 146.5, 137.6, 135.8,
131.0, 129.5. IR (ATR) υ/cm 3140 (C-H), 3082 (C-H),
1705 (C=O), 1599 (C=C).
¹1
21 Isophthaloyl diimidazole (1c) was prepared in a similar
manner to 1b with imidazole instead of 1,2,4-triazole. mp:
1
Supporting Information is available on http://dx.doi.org/
10.1246/cl.171098.
138.0-140.0 °C. H NMR (400 MHz, CDCl3, 26 °C): δ/ppm
8.24 (t, J = 1.8 Hz, 1H, a), 8.10 (dd, J1 = 7.4 Hz,
J2 = 1.8 Hz, 2H, b), 8.09 (br, 2H, f), 7.81 (t, J = 7.4 Hz,
1H, c), 7.54 (t, J = 1.5 Hz, 2H, e), 7.22 (dd, J1 = 1.5 Hz,
J2 = 0.8 Hz, 2H, d). 13C NMR (100 MHz, CDCl3, 26 °C):
δ/ppm 165.1, 138.5, 134.5, 133.8, 132.2, 131.3, 130.4,
References and Notes
1
S. R. Turner, Y. Liu, in Polymer Science: A Comprehensive
Reference, ed. by K. Matyjaszewski, M. Möller, Elsevier,
Waltham, 2012, Vol. 5, Chap. 5.14, pp. 311-331.
doi:10.1016/B978-0-444-53349-4.00143-6.
¹1
118.4. IR (ATR) υ/cm 3144 (C-H), 3117 (C-H), 1707
(C=O), 1602 (C=C).
2
A. M. Nelson, A. M. Pekkanen, N. L. Forsythe, J. H.
Herlihy, M. Zhang, T. E. Long, Biomacromolecules 2017,
18, 68.
L. Wu, R. Mincheva, Y. Xu, J.-M. Raquez, P. Dubois,
Biomacromolecules 2012, 13, 2973.
Y. Tachibana, T. Masuda, M. Funabashi, M. Kunioka,
Biomacromolecules 2010, 11, 2760.
U. K. Thiele, Chem. Fibers Int. 2004, 54, 162.
Q. Lin, Y. Gu, D. Chen, Appl. Polym. Sci. 2013, 129, 2751.
B. Xiao, L. Wang, R. Mei, G. Wang, J. Polym. Res. 2011, 18,
2221.
22 A typical procedure of solution polymerization (Run 1): A
solution of 1a (1.32 g, 6.49 mmol) in CH2Cl2 (10 mL, Wako,
Super Dehydrated) was added to a solution of 2a (0.585 g,
6.49 mmol) and Et3N (1.31 g, 13.0 mmol) in CH2Cl2 (3 mL)
at 0 °C in the presence of Na2SO4 under dry N2 atmosphere.
The reaction mixture was stirred for 1 h at the ambient
temperature and poured into hexane (100 mL). The precip-
itate was collected by filtration, washed with hexane (10 mL)
and H2O (10 mL) and dried in vacuo to afford the corre-
sponding polyester (1.41 g, 99% yield) as a colorless solid.
Mn (SEC) = 2500, Đ (SEC) = 1.28; Mn (NMR) = 4267.
23 A typical procedure of melt polymerization (Run 5): A
mixture of 1a (92 mg, 0.45 mmol) and 2b (93 mg,
0.46 mmol) was heated at 180 °C for 3 h under argon
atmosphere. After cooling, the product was dissolved in
CHCl3 and poured into hexane to afford the corresponding
polyester (140 mg, 80% yield) as a colorless solid. Mn
(SEC) = 23100, Đ (SEC) = 1.53. For the polymerization
of 1b, 1c, and 3b, the reaction system was evacuated
down to 375 Torr after the temperature reached the targeted
temperature.
3
4
5
6
7
8
9
P. Buzin, M. Lahcini, G. Schwarz, H. R. Kricheldorf,
Macromolecules 2008, 41, 8491.
M. Garaleh, M. Lahcini, H. R. Kricheldorf, S. M. Weidner,
J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 170.
10 T. Moyori, T. Tang, A. Takasu, Biomacromolecules 2012,
13, 1240.
11 A. Takasu, T. Makino, S. Yamada, Macromolecules 2010,
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12 A. Takasu, Y. Iio, T. Mimura, T. Hirabayashi, Polym. J.
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13 A. Takasu, Y. Iio, Y. Oishi, Y. Narukawa, T. Hirabayashi,
Macromolecules 2005, 38, 1048.
24 1c was soluble in melted 2b and thus the melt polymerization
could be conducted below the melting point of 1c.
14 H. R. Kricheldorf, M. Rabenstein, M. Maskos, M. Schmidt,
Macromolecules 2001, 34, 713.
15 J. A. Moore, J. E. Kelly, Polymer 1979, 20, 627.
16 J. S. Moore, S. I. Stupp, Macromolecules 1990, 23, 65.
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19 Y. Kimura, Jpn. Kokai Tokkyo Koho 2013-231027A;
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25 H. A. Staab, Angew. Chem., Int. Ed. Engl. 1962, 1, 351.
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27 CH2Cl2 and DMF was dried over molecular sieves 4A
overnight. A solution of 3a (2.9 g, 9.8 mmol) in CH2Cl2
(15 mL) and DMF (1 mL) was added dropwise to a
suspension of 1,2,4-triazole (2.8 g, 41 mmol) in CH2Cl2
(35 mL) and DMF (1 mL). The reaction mixture was stirred
for 2.5 h. Water (50 mL) was added and the organic layer was
separated and the aqueous layer was extracted with CH2Cl2
(15 mL). The combined organic layer was washed with water
(50 mL) and sat. NaHCO3 aq (50 mL © 2), dried over
Na2SO4 and concentrated. The residue was dried at 80 °C
for 1 h to afford 3b (2.52 g, 71% yield) as white crystal.
20 Isophthaloyl bis(1,2,4-triazole) (1b): A slurry of 1,2,4-
triazole (42.2 g, 0.611 mol) in CH2Cl2 (200 mL) was added
dropwise to a solution of 1a (30.7 g, 0.151 mol) in CH2Cl2
(25 mL) over 30 min. The solution was stirred at ambient
temperature for 1 h, and then water (100 mL) was added. The
organic layer was collected and washed with water (200 mL)
twice and dried over Na2SO4. The solvent was removed
under reduced pressure to afford 1b (39.7 g, 98.8% yield)
1
mp 163.0-163.8 °C; H NMR (400 MHz, DMSO-d6, 26 °C):
δ/ppm 9.44 (s, 2H, d), 8.39 (s, 2H, c), 8.25-8.21 (m, 4H, a),
7.35-7.31 (m, 4H, b). 13C NMR (100 MHz, DMSO-d6,
26 °C): δ/ppm 164.6, 161.1, 154.5, 147.9, 135.4, 126.8,
¹1
119.8. IR (ATR) υ/cm 3140 (C-H), 3119 (C-H), 1701
(C=O), 1593 (C=C).
1
as colorless solid. mp: 119.0-119.4 °C. H NMR (400 MHz,
28 R. Seto, T. Kojima, K. Hosokawa, Y. Koyama, G. Konishi,
T. Takata, Polymer 2010, 51, 4744.
CDCl3, 26 °C): δ/ppm 9.18 (t, J = 1.3 Hz, 1H, a), 9.15
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