Synthesis and characterization of trans-di(nitrobenzo)- and di(aminobenzo)-18-crown-6 derivatives with high selectivity

Article abstract of DOI:10.1080/00397911.2017.1402350

The dibenzo-18-crown-6 derivatives such as di(nitrobenzo)-18-crown-6 and di(aminobenzo)-18-crown-6 were synthesized by nitration reaction and catalytic hydrogenation with high selectivity. The chemical structures were determined by FTIR, ¹H NMR, ¹³C NMR, and UV. Regarding the mixture of Ac₂O and HNO₃ as nitrating agent, the reaction exhibited commendable trans-isomer selectivity. Effects of nitrating agent ratio, reaction temperature and reaction time on yield of trans-di(nitrobenzo)-18-crown-6 were investigated. The yield of trans-di(nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1/1, reaction temperature of 50 °C and reaction time of 5 h. Moreover, effect of reaction time on trans-di(aminobenzo)-18-crown-6 was also studied.

Full text of DOI:10.1080/00397911.2017.1402350

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Synthesis and characterization of trans-
di(nitrobenzo)- and di(aminobenzo)-18-crown-6
derivatives with high selectivity
Dongyun Wu, Chunhai Yi, Beibei Zhang & Bolun Yang
To cite this article: Dongyun Wu, Chunhai Yi, Beibei Zhang & Bolun Yang (2018): Synthesis and
characterization of trans-di(nitrobenzo)- and di(aminobenzo)-18-crown-6 derivatives with high
selectivity, Synthetic Communications, DOI: 10.1080/00397911.2017.1402350
To link to this article: https://doi.org/10.1080/00397911.2017.1402350
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Date: 08 January 2018, At: 16:21

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https://doi.org/10.1080/00397911.2017.1402350
Synthesis and characterization of trans-di(nitrobenzo)- and
di(aminobenzo)-18-crown-6 derivatives with high selectivity
Dongyun Wu, Chunhai Yi, Beibei Zhang, and Bolun Yang
Shaanxi Key Laboratory of Energy Chemical Process Intensification, School of Chemical Engineering and
Technology, Xi’an Jiaotong University, Xi’an, P.R. China
ABSTRACT
ARTICLE HISTORY
Received 6 April 2017
The dibenzo-18-crown-6 derivatives such as di(nitrobenzo)-18-
crown-6 and di(aminobenzo)-18-crown-6 were synthesized by
nitration reaction and catalytic hydrogenation with high selectivity.
The chemical structures were determined by FTIR, H NMR, C NMR,
and UV. Regarding the mixture of Ac O and HNO as nitrating agent,
KEYWORDS
Catalytic hydrogenation;
high selectivity; nitration
reaction; trans-di
1
13
2
3
the reaction exhibited commendable trans-isomer selectivity. Effects of
nitrating agent ratio, reaction temperature and reaction time on yield of
trans-di(nitrobenzo)-18-crown-6 were investigated. The yield of trans-di
(aminobenzo)-18-crown-6;
trans-di(nitrobenzo)-18-
crown-6
(
nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1/1,
reaction temperature of 50 °C and reaction time of 5 h. Moreover, effect
of reaction time on trans-di(aminobenzo)-18-crown-6 was also studied.
GRAPHICAL ABSTRACT
Introduction
In 1967, Pedersen[1] at DuPont first synthesized the dibenzo-18-crown-6, and found that it
possessed the selective cation-complexing properties. From then on, the research of crown
ethers arouses great interest, and numerous types of crown ethers have been synthesized
through approximate 50 years of development. Crown ethers are cyclic chemical
compounds that consist of a ring including several ether groups. The most common crown
ethers are cyclic oligomers of ethylene oxide, and the repeating unit is ethyleneoxy,
–
CH CH O–. Furthermore, crown ether derivatives containing other heteroatom are also
2 2
synthesized, such as oxa-aza crown ether, azacrown ether, and thiacrown ether.
At present, crown ethers have been extensively applied in organic chemical reaction,
polymerization reaction, inorganic chemistry, analytical chemistry, enrichment and
[
2–7]
separation of metal ions, and separation of chiral compounds.
For instance, B15C5
CONTACT Chunhai Yi
chyi@mail.xjtu.edu.cn
Shaanxi Key Laboratory of Energy Chemical Process Intensification,
School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an 710049, P.R. China.
Supplemental data for this article can be accessed on the publisher’s website.
©
2017 Taylor & Francis

2
D. WU ET AL.
was chosen as lithium isotopes separation extractant because its cavity size was closed to
þ [8]
the ionic diameter of Li . Since the micromolecule crown ethers have certain physiologi-
cal toxicity, the derivatives of crown ethers have been synthesized for the enrichment and
[
9–13]
separation of metal ions, catalytic reaction and reverse osmosis membranes.
Yakshin
[
14]
et al.
synthesized the cis-di(nitrobenzo)-18-crown-6, trans-di(nitrobenzo)-18-crown-6,
cis-di(aminobenzo)-18-crown-6 and trans-di(aminobenzo)-18-crown-6 for metal salt sorp-
tion from aqueous chloride solutions, and found that trans-di(nitrobenzo)-18-crown-6
possessed the highest sorption efficiency. Despite the superior property of trans-derivate,
there are very few reports on the product selectivity for cis- and trans-derivates. Although
[
15]
[16]
Feigenbaum and Michel
and Saigo et al.
synthesized the di(nitrobenzo)-18-crown-6,
the content of cis-isomer was almost the same as trans-isomer.
In this paper, derivates of dibenzo-18-crown-6 (DB18C6) were synthesized with high
selectivity for trans-product. The physical properties of di(nitrobenzo)-18-crown-6 and di
1
13
(
aminobenzo)-18-crown-6 were characterized by FTIR, H NMR, C NMR and UV. The
effects of synthesis parameters on yield of trans-di(nitrobenzo)-18-crown-6 and trans-di
aminobenzo)-18-crown-6 were investigated, and reaction conditions were optimized.
(
Discussion
The syntheses of DB18C6 derivatives are described in Scheme 1. The synthetic method is
notable as it is easy to operate and shows a very high trans-selectivity. Di(nitrobenzo)-18-
crown-6 was obtained from DB18C6 by nitration reaction. The product possessed a
Scheme 1. Reaction equations of di(nitrobenzo)-18-crown-6 and di(aminobenzo)-18-crown-6.

SYNTHETIC COMMUNICATIONS®
3
commendable selectivity for trans-di(nitrobenzo)-18-crown-6 compared with other
[
15,16]
literatures.
The corresponding di(aminobenzo)-18-crown-6 was obtained through
catalytic hydrogenation of the nitro group.
In this work, a mixture of HNO and Ac O as a low active nitrating agent was selected
3
2
for the nitration of DB18C6 due to the fact that DB18C6 contains the ether groups (–O–),
which are connected with the benzo ring and thus can promote the nitration reaction. The
effect of nitrating agent ratio on the yield of trans-di(nitrobenzo)-18-crown-6 was studied.
As shown in Table 1, the yield of trans-di(nitrobenzo)-18-crown-6 can reach up to 41.4%
when the molar ratio of Ac O/HNO was 1/1. By contrast, the yield decreased to only
2
3
2
7.9% with Ac O/HNO molar ratio of 1.5/1, and no desired production can be detected
2 3
for its molar ratio of 0.5/1. It means that the optimal proportion of Ac O/HNO for the
2
3
maximum yield of trans-di(nitrobenzo)-18-crown-6 is 1/1.
The reaction mechanism of the nitrating agent is mentioned below.
HNO þ ðCH COÞ O Ð CH CO NO þ CH COOH
3
3
2
3
2
2
3
HNO þ CH COOH Ð CH CO NO þ H O
3
3
3
2
2
2
ðCH COÞ O þ H O Ð 2CH COOH
3
2
2
3
The reaction product of HNO and Ac O is acetyl nitrate, which is nitrating agent with
3
2
high reaction activity. Thus, the acetyl nitrate is the real nitrating agent in this reaction. On
one side, Ac O can remove the water produced in step two and promote the nitrating
2
reaction process. On the other side, the excessive Ac O is likely to bring about the vice-
2
product, and reduce the yield of trans-di(nitrobenzo)-18-crown-6. Therefore, the optimum
proportion of Ac O/HNO is 1/1.
2
3
The effect of reaction temperature on yield of di(nitrobenzo)-18-crown-6 was
investigated subsequently (Fig. 1). The results showed that the yield of trans-di(nitro-
benzo)-18-crown-6 reached to a maximum and then decreased with increasing the reaction
temperature. While the yield of cis-di(nitrobenzo)-18-crown-6 increased obviously with the
reaction temperature. The highest yield of trans-di(nitrobenzo)-18-crown-6 reached 41.4%
at the reaction temperature of 50 °C. When reaction temperature was below 50 °C, trans-di
(
nitrobenzo)-18-crown-6 yield increased with the reaction temperature due to the increase
in reaction rate. For the reaction temperature higher than 50 °C, the cis-di(nitrobenzo)-18-
crown-6 yield increased obviously, which led to a decline in trans-di(nitrobenzo)-18-
crown-6 yield. Thus the optimal point of reaction temperature for the largest production
of trans-di(nitrobenzo)-18-crown-6 is 50 °C.
The effect of reaction time on yield of di(nitrobenzo)-18-crown-6 was displayed in
Figure 2. It was observed that the yield of trans-di(nitrobenzo)-18-crown-6 increased with
the increase of reaction time, and reached to 62.9% when the reaction time was 5 h. However,
due to the existence of multiple nitration by-products, the reaction yield would decrease if the
reaction time continued to extend; therefore, the optimum reaction time is 5 h.
Table 1. Yield of di(nitrobenzo)-18-crown-6 for varied ratios of nitrating agent.*
Nitrating agent ratio/(mol/mol)
Ac
2
O/HNO
3
¼ 0.5/1
Ac
2
O/HNO
3
¼ 1/1
Ac
2
O/HNO
3
¼ 1.5/1
Trans-di(nitrobenzo)-18-crown-6
Cis-di(nitrobenzo)-18-crown-6
None
None
41.4
5
27.9
1.2
*Reaction time: 6 h, reaction temperature: 50 °C.

4
D. WU ET AL.
Figure 1. Yield of di(nitrobenzo)-18-crown-6 for different reaction temperature (Ac O/HNO molar
2
3
ratio: 1/1, reaction time: 6 h).
Figure 3 listed the comparison of di(nitrobenzo)-18-crown-6 yield between the current
work and the references. Feigenbaum and Michel[15] and Deetz et al.[17] synthesized di
(
nitrobenzo)-18-crown-6 from DB18C6 nitrated with a mixture of nitric acid and acetic
acid, and found that the percentages of trans-di(nitrobenzo)-18-crown-6 were 57.5% and
2.4%, respectively. In this study, the percentage of trans-di(nitrobenzo)-18-crown-6
accounted for 93.7% nitrated with a mixture of Ac O and HNO , indicating that the
5
2
3
nitration agent possessed a high selectivity with trans-di(nitrobenzo)-18-crown-6 yield of
6
2.9% at the optimal condition.
Trans-di(aminobenzo)-18-crown-6 was prepared by the catalytic hydrogenation of
trans-di(nitrobenzo)-18-crown-6. As shown in Figure 4, the productivity of trans-di(ami-
nobenzo)-18-crown-6 increased gradually with the increase of reaction time. However,
there was only 3.8% increase in the trans-di(aminobenzo)-18-crown-6 yield when the
Figure 2. Yield of di(nitrobenzo)-18-crown-6 for different reaction time (Ac O/HNO molar ratio: 1/1,
2
3
reaction temperature: 50 °C).

SYNTHETIC COMMUNICATIONS®
5
Figure 3. Yield of di(nitrobenzo)-18-crown-6 obtained in this study compared with the references.
reaction time was prolonged from 2 to 4 h. Therefore, the optimum reaction time is set
as 2 h.
In conclusion, the derivatives obtained from DB18C6 were synthesized by nitration
reaction and catalytic hydrogenation. The chemical structures of di(nitrobenzo)-18-
1
13
crown-6 and di(aminobenzo)-18-crown-6 were certified by FTIR, H NMR, C NMR,
and UV. Using Ac O and HNO as nitrating agent, the nitration reaction can obtain a
2
3
commendable selectivity, and the main product was trans-di(nitrobenzo)-18-crown-6.
The yield of trans-di(nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1,
reaction temperature of 50 °C and reaction time of 5 h. The di(aminobenzo)-18-crown-6
was prepared from di(nitrobenzo)-18-crown-6 by catalytic hydrogenation. The reaction
yield of trans-di(aminobenzo)-18-crown-6 was 76.2% for the catalyst and trans-
di(nitrobenzo)-18-crown-6 ratio of 0.04 (wt), hydrogen pressure of 0.35 MPa, reaction
temperature of 70 °C and reaction time of 2 h.
Figure 4. Yield of trans-di(aminobenzo)-18-crown-6 for different reaction time (hydrogen pressure:
0.35 MPa, reaction temperature: 70 °C).

6
D. WU ET AL.
Experimental section
General
Nitric acid, N,N-dimethyl formamide (DMF), ethylene glycol monomethyl ether, ethanol,
acetic acid, trichloromethane and 10 wt% Pd/C catalyst were purchased from Sinopharm
Chemical Reagent Co., Ltd. Acetic anhydride was purchased from West Long Chemical
Co., Ltd. Dibenzo-18-crown-6 (DB18C6, 98%) was purchased from J&K Scientific Co.,
Ltd of Beijing, China. DMF and ethylene glycol monomethyl ether were purified by 5A
molecular sieves before using. The other chemicals were used as received. Melting points
were determined on the YRT-3 melting-point apparatus with open-ended capillary tubes.
The UV spectrum was tested by UV-1900PPC. The element analysis was tested by Vario EL
Ⅲ
. The FTIR spectra were measured with Nicolet Avatar 360 instrument with OMNI-
−
1
1
13
sampler. The resolution of FTIR is 4 cm . H NMR spectra and C NMR spectrum were
measured on the Bruker AVIII 500WB at 60 °C and Bruker Avance 400 MHz at room
temperature, respectively. The chemical shifts were recorded with tetramethylsilane as
the internal standard.
Trans-di(nitrobenzo)-18-crown-6
About 5.1000 g of DB18C6, 105 mL of trichloromethane and 75 mL of acetic acid were
added into a 250 mL round-bottomed flask equipped with a mechanical stirrer, and dis-
solved at room temperature. Then the mixture of acetic anhydride and nitric acid was
added dropwise. The reaction mixture was refluxed at 50 °C for 5 h and then filtered.
The filter cake was trans-di(nitrobenzo)-18-crown-6 and recrystallization was used by
DMF at 150 °C. Trans-di(nitrobenzo)-18-crown-6 was obtained as a white powder by
[
15,17]
removing solvent in vacuum. Mp. 236.8–238.6 °C, lit
247–252 °C or 237–242 °C. FTIR
−1 1
(
KBr) 1592, 1516, 1346 (–NO ), 897, 882 (C–N) cm . H NMR (500 MHz, DMSO) δ
2
7
.87 (dd, 2H, J ¼ 9, 2.6 Hz), 7.73 (d, 2H, J ¼ 2.6 Hz), 7.16 (d, 2H, J ¼ 9 Hz), 4.24 (m,
8
H), 3.88 (m, 8H). UV (99.7% ethanol): λ (log ε) ¼ 340 (4.47). Anal. Calcd for
max
C H N O : C, 53.33; H, 4.89; N, 6.22%. Found: C, 53.12; H, 4.91; N, 6.18%.
2
0
22 2 10
Trans-di(aminobenzo)-18-crown-6
About 1.6500 g of above-produced trans-di(nitrobenzo)-18-crown-6 was dissolved in
1
00 mL ethylene glycol monomethyl ether, and subsequently 0.0660 g of 10 wt% Pd/C
catalyst was added into cooled solution. The reaction was peformed at 70 °C under hydro-
gen pressure of 0.35 MPa for 2 h. The mixture was cooled to room temperature, discharged
after the pressure released, and filtered to remove the Pd/C. The filtrate was distilled to
remove the solvent under vacuum, and the crude trans-di(aminobenzo)-18-crown-6 pro-
duct was recrystallized from the mixture of ethylene glycol monomethyl ether and ethanol.
Trans-di(aminobenzo)-18-crown-6 of light brown powder was gained by removing solvent
[
15]
in vacuum. Mp. 187–191 °C, lit 199–203 °C. FTIR (KBr) 3428, 3353 (–NH ), 1613, 1515,
2
−
1 1
1
278 (C–N) cm . H NMR (500 MHz, DMSO) δ 6.65 (d, 2H, J ¼ 8.4 Hz), 6.27 (d, 2H,
J ¼ 2.2 Hz), 6.09 (dd, 2H, J ¼ 8.4, 2.4 Hz), 4.52 (s, 4H), 4.03–3.94 (m, 8H), 3.85–3.77
1
3
(
6
m, 8H). C NMR (100 MHz, DMSO) δ 149.7, 143.9, 139.6, 116.1, 105.8, 101.1, 69.9,
9.6, 69.5, 68.2. UV (99.7% ethanol): λmax (log ε) ¼ 295 (4.53). Anal. Calcd for
C H N O : C, 61.54; H, 6.67; N, 7.18%. Found: C, 61.52; H, 6.62; N, 6.87%.
2
0
26 2 6

SYNTHETIC COMMUNICATIONS®
7
Funding
This work is supported by the National Key R&D Program of China (2017YFB0603402), the
National Natural Science Foundation of China (21576217), and the Fundamental Research Funds
for the Central Universities (xjj2016044).
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