High efficiency microwave-assisted synthesis of quinoline from acrolein diethyl acetal and aniline utilizing Ni/Beta catalyst

Article abstract of DOI:10.1016/j.catcom.2018.06.024

A facile and solvent-free microwave-assisted approach to quinoline was developed by utilizing both acrolein diethyl acetal and aniline as reagents, firstly employing Ni/Beta zeolite as mild, ecofriendly and low-cost solid catalyst. As high as 83% yield of quinoline was quickly achieved at a short microwave time. The results indicated that the effect of Ni on Beta zeolite not only significantly promoted conversion of acrolein diethyl acetal to effective intermediate but also dramatically accelerated dehydrogenation rate of tetrahydroquinoline/dihydroquinoline to quinoline.

Full text of DOI:10.1016/j.catcom.2018.06.024

Accepted Manuscript
High efficiency microwave-assisted synthesis of quinoline from
acrolein diethyl acetal and aniline utilizing Ni/Beta catalyst
An Li, Zan Yang, Tao Yang, Cai-Wu Luo, Zi-Sheng Chao, Cong-
Shan Zhou
PII:
DOI:
Reference:
S1566-7367(18)30237-1
doi:10.1016/j.catcom.2018.06.024
CATCOM 5439
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
18 April 2018
20 June 2018
25 June 2018
Please cite this article as: An Li, Zan Yang, Tao Yang, Cai-Wu Luo, Zi-Sheng Chao, Cong-
Shan Zhou , High efficiency microwave-assisted synthesis of quinoline from acrolein
diethyl acetal and aniline utilizing Ni/Beta catalyst. Catcom (2018), doi:10.1016/
j.catcom.2018.06.024
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ACCEPTED MANUSCRIPT
High
efficiency
microwave-assisted
synthesis of quinoline from acrolein diethyl
acetal and aniline utilizing Ni/Beta catalyst
An Li,a Zan Yang,a Tao Yang,a Cai-Wu Luo,b Zi-Sheng Chao*c and
Cong-Shan Zhou*a
a
College of Chemistry and Chemical Engineering, Hunan Institute of
Science and Technology, Yueyang, 414000, China. E-mail:
zhoucongsh@126.com.
b School of Environmental and Safety Engineering, University of South
China, Hengyang 421001,China
c
College of Materials Science and Engineering, Changsha University
of Science &Technology, Changsha, Hunan 410114, China. E-mail:
zschao@yahoo.com
*Corresponding
author.
Email:
zschao@yahoo.com
and
zhoucongsh@126.com.

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ABSTRACT
A facile and solvent-free microwave-assisted approach to quinoline
was developed by utilizing both acrolein diethyl acetal and aniline as
reagents, firstly employing Ni/Beta zeolite as mild, ecofriendly and
low-cost solid catalyst. As high as 83% yield of quinoline was quickly
achieved at a short microwave time. The results indicated that the effect
of Ni on Beta zeolite not only significantly promoted conversion of
acrolein diethyl acetal to effective intermediate but also dramatically
accelerated dehydrogenation rate of tetrahydroquinoline/dihydroquinoline
to quinoline.
Keywords: microwave-assisted, acrolein diethyl acetal, quinolines, Beta
zeolite

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1. Introduction
Quinolines(Quinoline and its derivatives), as an important class of
nitrogen heterocyclic compounds, have extensive application prospects in
various fields. In particular, quinoline can act as a building block for the
preparation of a wide range of value-added products applied in many
industries such as pharmaceuticals, fungicides, herbicides, corrosion
inhibitors and functional chemicals.[1-6] The typical quinolines synthesis
methods involved Skraup[7, 8], Friedlander[9, 10], Doebner-Miller[11,
12], Conrad-Limpach[13, 14] and other methods[15-17], which could be
carried out via conventional liquid-phase, vapor-phase or microwave
route. Among these routes, compared with conventional thermal
conditions requiring long reaction time and poisonous organic solvent,
the microwave-assisted route is straightforward, quickly, solvent-free and
heating evenly, which play more and more important role in quinolines
synthetic strategy.
Up to now, there are many literature reports relating to
microwave-assisted synthesis of quinoline derivatives, but most of them
employed various unsaturated aldehydes/ketones or alkynes as one of
reagent, such as alkyl vinyl ketones[18, 19], crotonaldehyde[20],
cinnamaldehyde[21] and phenylacetylene[22]. Unfortunately, unsaturated
aldehydes/ketones and alkynes as reagent were toxic, expensive and
prone to polymerization during reaction, which is difficult to fulfill strict

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requirements for environmental protection at present and then distinctly
restricts the further development of quinolines synthesis. acrolein diethyl
acetal(ADA), as a valuable chemical compound, possesses extraordinary
diffusion ability and chemical stability, which is usually used to protect
carbonyl group and also significantly avoids acrolein’s relatively high
cost and propensity to oligomerize when acrolein was directly used as
reagent.[23, 24] Moreover, the procedure for the preparation of acetal is
straightforward, which could be directly produced by corresponding
aldehydes/ketones with alcohols with high conversion as well as excellent
selectivity[23, 25]. Recently, Bryan J. Cowen reported that the reaction of
ADA and aniline could obtain quinoline with high yield[26]; the only
drawback is the reaction time up to 24 h under traditional thermal
condition. Anyway, ADA shows a very promising future in quinolines
synthetic reactions.
In the microwave-assisted synthetic quinolines routes, sulfuric acid,
K10, InCl3/SiO2, phosphotungstic acid, AgOTf/NH4PF6, CuCl/Mont,
functionalized-ionic liquid were usually employed as catalyst[18-22],
which existed low selectivity, expensive or not environment-friendly at
present. On the contrary, metal-modified zeolite possess large surface
area, excellent hydrothermal stability as well as flexible adjustable active
sites, which was utilized as catalyst to synthesize quinolines and
exhibited excellent catalytic performance previously in conventional

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liquid- or vapor-phase synthetic routes[27, 28]. Hence, in the presence
work, a facile, fast and solvent-free microwave-assisted approach to
quinoline utilizing ADA as one of reagent was provided, firstly
employing metal-loaded zeolite as mild, ecofriendly and low-cost solid
catalyst. High yield of quinoline was achieved over Ni/Beta catalyst
undergo short microwave reaction time.
2. Experimental
2.1. Catalysts preparation
The Beta, ZSM-5, and Y zeolites were supplied by Nankai
University Catalyst Factory; and all the chemicals were commercially
available and had analytic purity. The metal-modified Beta catalysts were
prepared by deposition-precipitation method. The typical procedures were
as follows: The Beta zeolite powder was first added into the mixture
aqueous solution containing a calculated amount of 0.2 M Ni(NO3)2 and
excessive urea. The suspension was strongly stirred at room temperature
for 1 h and then heated to 90 °C to refluxing for 4 h. subsequently, the
resultant was cooled to room temperature, filtrated and washed with
deionized water. Finally, the obtained solid was dried at 120 °C for 12 h
and calcined at 550 °C for 4 h. The thus-prepared catalysts were denoted
as Ni/Beta. The similar preparation method for other metal (metal: Zn, Fe,
Cu and Mn) oxides supported catalysts.
2.2. Catalytic performance evaluation

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General procedure for synthesis of quinolines from anilines and
ADA was carried out in Panasonic NN-K5541JF microwave oven reactor
equipping a magnetic stirring device. The typical procedures were as
follows: ADA (1 mmol), excessive anilines (4 mmol) and solid catalyst
were charged into a round-bottom flask; and then, the mixtures was
placed into microwave reactor. The reaction was conducted by continuous
microwave irradiation for 1-40 min under refluxing and stirring condition.
Finally, the resulting products were determined by GC-MS of Varian
Saturn 2200/ CP-3800 gas chromatography–mass spectrometry equipped
with two CP8944 capillary columns (VF-5, 30 m × 0.25 mm × 0.25 μm).
2.3. Catalysts Characterization
X-ray diffraction spectroscopy was performed with a Bruker
D8-Advance X-ray diffractometer. The detection conditions as follow:
Cu target Kα ray (λ=1.54187 Å); scanning voltage 40 kV, scanning
current 40 mA; scanning speed 0.2 s, scanning step 0.02o.
N2-physisorption was conducted on a Quantachrome Autosorb-1
instrument. Firstly, the catalyst was in situ outgassed at 300 °C for 12 h
under a vacuum of 10-8 Torr. Subsequently, the specific surface area was
calculated by multipoint BET equation, and the total pore volume was
calculated at relative pressure of P/P0=0.99. Temperature programmed
desorption of NH3 was determined on a Micromeritics Autochem II 2920
instrument. Firstly, the catalyst was pretreated at 400 °C for 30 min in a

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flow of helium (99.99%) with a flow rate of 60ml/min and then cooled to
100 °C. Ammonia was pulse-injected in a stream of 10 % NH3/He to
achieve saturation adsorption of catalyst. After purging with helium at
100 °C for 1.0 h, ammonia was desorbed by heated the catalyst from
100 °C to 800 °C at a rate of 10 °C/min.
3. Results and discussion
3.1. Catalysts performances
Table 1 shows catalytic performances of various catalysts for
microwave-assisted synthesis of quinoline from ADA and aniline. When
various parent zeolites are used as catalysts respectively, the yield of
quinoline is extremely low with low conversion of ADA. The completion
of this reaction is considered to undergo two steps, containing
decomposition of ADA to acrolein and/or other intermediate and
subsequent condensation with aniline to quinoline, as shown in Eqs. (1).
Thus, the terrible catalytic activity of pure zeolites is probably due to the
low decomposition of ADA to effective intermediate. When various
metal-loaded Beta zeolites are used as catalyst, respectively, both
conversion of ADA and yield of quinoline increase sharply; and
particularly as high as 83.1% yield of quinoline with complete conversion
of ADA is achieved over Ni/Beta catalyst. The result indicates that the
addition of metal on Beta zeolite catalyst significantly promote

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decomposition of ADA to effective intermediate and subsequently
condensation with aniline to form target product. Furthermore, when
moderate water is added into reaction system, the yield of quinoline
slightly decreases instead. Besides, the amount of catalyst also affects the
conversion of ADA as well as yield of quinoline, as shown in Fig. S1.
With increasing amount of catalyst, both conversion of ADA and yield of
quinoline firstly increase obviously and subsequent decrease slightly,.
This result is probably due that, more active sites could be provided to
complete this reaction with appropriate increasing amount of catalyst,
however, excessive active sites may be induce some side reactions, such
as alkylation of quinoline, deep decompose of ADA and et. al, which
decrease the yield of quinoline.
Fig.1 shows the effect of microwave time for quinoline yield over
Beta and Ni/Beta catalysts. with increasing microwave irradiation time,
the yield of quinoline just reaches to 32.1% after 40 min over the Beta
catalyst, while that of quinoline sharply increases to 83.1% after 5 min
over the Ni/Beta catalyst. The results show that, relative to the Beta
catalyst, the Ni/Beta one is capable to accomplish much higher yield of
quinoline under extremely short microwave time. This occurs probably
due to the fact that the Ni-loaded on Beta zeolite accelerates the
decomposition of ADA to effective intermediate and promotes the
formation of quinoline subsequently under microwave reaction condition.

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Therefore, the Ni/Beta catalyst exhibits high-effective catalytic
performance. What is more, the Ni/Beta catalyst possesses a good
recyclable performance, and its catalytic activity is near same to the fresh
one after reusing four times under microwave and free-solvent condition,
as shown in Fig. S2.
Fig.2 shows the effect of reaction time for product distribution over
Beta(I) and Ni/Beta(II) catalyst. By means of mass spectrometric
detection for product mixtures, it confirms that, besides quinoline,
dihydroquinoline (2HQ) and tetrahydroquinoline (4HQ) are also
generated during the reaction, as shows in Fig. S3. Over the Beta catalyst,
high yield of 2HQ and 4HQ, which even exceeds that of quinoline, are
obtained with 5 min microwave reaction; and meanwhile, the yield of
4HQ increases in entire reaction process while that of 2HQ increases
firstly and decreases generally subsequently with increasing microwave
time. Finally, the total yield of 4HQ and 2HQ still reaches to 23% after 40
min microwave irradiation. the result indicates that, with increasing
microwave irradiation time, ADA is cracked and further condensed with
aniline to form more 4HQ; and meanwhile, certain 2HQ is
dehydrogenized to quinoline especially during 10-20 min reaction time.
Besides, it is noteworthy that the level of side reactions also increase with
prolonging reaction time over the Beta catalyst. Over the Ni/Beta catalyst,
the total yield of 4HQ and 2HQ is 22% with 1 min microwave reaction

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time, while that of 4HQ and 2HQ significantly decreases to 3.5% after
only 5 min microwave reaction time; and meanwhile, the conversion of
ADA is much higher than that over the Beta catalyst. The results indicate
that, relative to the Beta catalyst, the Ni/Beta catalyst not only
significantly accelerates the conversion of ADA but also effectively
promote the process of dehydrogenation of 4HQ and 2HQ to quinoline.
Table 2. shows the reaction of ADA with various substituted anilines
over Ni/Beta catalyst. Such as, o-, m- or p-methylaniline reacts with ADA
to deliver 8-, 7- or 6-methylquinoline in 58.4%, 41.3% and 66.8% yield,
respectively. Weak results are obtained with m- or o-nitroaniline reacting
with ADA to deliver target quinolines products with just 25.8% and
19.4% yield, and the reaction of 2-hydroxyaniline and ADA delivers
31.3% yield of 7-hydroxyquinoline. Besides, o- and p-methoxyaniline
reacts with ADA can obtain 65.3% and 57.2% yield of corresponding
substitute quinoline, respectively; while the reaction of o-/p-chloroaniline
and ADA delivers 8-/6-chloroquinoline in only 32.1% and 27.9% yield. It
is noteworthy that, relative to aniline, other various substituted anilines
reacting with ADA result in the decreased yield of desired quinolines, to
different extent; and particularly, the yield of quinolines decreases more
obviously using substituted aniline with electrondrawing group as reagent.
This occurs probably due to the negative effects of stereo-hindrance of
substituent group on benzene ring and/or the restraint of the condensation

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of substitute anilines and intermediate because of the existence of
electrondrawing group.
the reactions of other reagent and aniline to form desired quinolines
also were investigated, as shown in table 1S. Glycerol and acetaldehyde
as reagent respectively reacting with aniline can not generated quinoline
or methylquinoline, probably due to the difficulty of glycerol dehydrating
to intermediate acrolein or the leaving of acetaldehyde from reaction
system rapidly because of its high volatility under microwave
environment. Furthermore, acrolein directly as reagent reacting with
aniline indeed synthesizes quinoline, but the yield of quinoline is very
low (31.6 %) with full conversion of acrolein, which may arise from
acrolein side reactions and/or fast volatility from reaction system.
Relative to acrolein, ADA not only retains high chemical activity of
olefinic bond but also protects its carbonyl group via acetalization which
could restrain the level of side reactions effectively. Therefore, among
various raw materials, ADA as the optimized reagent reacting with aniline
can achieve high yield of quinoline.
3.2. Catalysts characterization
The Beta, Ni/Beta and reused-Ni/Beta catalysts are characterized by
XRD, BET and NH3-TPD methods. XRD patterns for catalysts are shown
in Fig. 4S. All the catalysts show the characteristic of Beta zeolite and
contain no diffraction peaks of Ni species for Ni/Beta catalysts, indicating

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that Ni species are highly dispersed on Beta zeolite. Besides, the
reused-Ni/Beta catalyst have almost same diffraction intensities relative
to the fresh one, implying that the structure of Ni/Beta is considerably
stable under microwave condition.
N2-adsorption/desorption isotherm are shown in Fig. 5S. The
isotherms of All the catalyst rise steeply at extremely low relative
pressure and exist a weak hysteresis loop at P/P0 > 0.4, indicating the
existence of microporous and some mesoporous probably deriving from
Beta secondary particle piled pore. The detailed textural properties of
catalysts are also listed in table 2S. the Ni/Beta catalyst has the smaller
surface area (SBET, Sext, Smic), pore volume (Vtotal, Vmic) as well as
micropore size (Dmic) than the pure Beta one. The decreased
microporosity of Ni/Beta is mainly due to certain occupation in
micropores by Ni component. Especially, the reused-Ni/Beta catalyst
shows little decrement of SBET, Sext, Smic and Vtotal, further indicating the
good stability of Ni/Beta catalyst after recycling.
The acidity property of catalyst are shown in Fig 6S. All the
catalyst exist T1 peak, attributing to weak acid sites.[29, 30] The T2 peak
is identified obviously over the Beta catalyst but virtually absent over the
Ni/Beta one, assigning to strong Brønsted acid sites. The T3 peak
appearing distinctly over Ni/Beta catalyst is attributed to strong Lewis
acid sites deriving from Ni-supported on Beta zeolite with certain

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interactions. The detail acidity date shows that, as listed in table 3S, the
Beta catalyst possesses a larger strong Brønsted acid sties while the
Ni/Beta one presents more strong Lewis acid sites; and especially,
concentration of both weak acid and strong Lewis acid over Ni/Beta
catalyst decreases little even if reuse four times. Therefore, combining
with catalyst performance, it is concluded that the introduction of Lewis
acid into Beta zeolite is favorable to generation of quinoline under
microwave condition.
3.3. Reactionpathways
Hence, a plausible reaction mechanisms from aniline and ADA
under microwave condition is speculated. ADA firstly converts to the
protonated acrolein and/or oxocarbenium ion[26], and then reacts with
aniline to generate unsaturated imine. Subsequently, imine reacts with
another aniline to form double-benzene-structured imine, which converts
to 4HQ via hydrogenolysis. Finally, the 4HQ transforms to 2HQ and
further delivers to quinoline via dehydrogenation. Besides, the
generated-protonated acrolein and/or oxocarbenium ion could react with
aniline to form aniline propanal via michael addition, and subsequent
generate quinoline via the process of cyclization, dehydration and
dehydrogenation. Still, the mechanism relating to synthesis of quinoline
form ADA and aniline under microwave condition (especially the
formation of 4HQ) in the present case is not fully understood, which need

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to be further investigated.
4. conclusion
A fast, facile and solvent-free microwave-assisted approach to
quinoline with ADA as one of reagents was provided, in which high yield
of quinoline was obtained utilizing Ni/Beta as mild, ecofriendly and
low-cost solid catalyst. The addition of Ni on catalyst not only
significantly promoted the conversion of ADA to effective intermediate
but also dramatically accelerated the dehydrogenation rate of
tetrahydroquinoline/dihydroquinoline to quinoline. Moreover, a series of
substituted quinolines are obtained, using various substituted anilines
reacting with ADA over Ni/Beta catalyst under microwave irradiation.

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Acknowledgments
This work was supported by National Natural Science Foundation of
China (No. 21476068, 21471053).

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Table captions
Table 1 Catalyst performance over various zeolite-base catalysts
a
b
c
Catalyst
Y
ADA:Cat:H2O
1:1:0
Conversion (%)
Yield (%)
19.3
22.7
25.4
27.2
95.5
98.2
85.2
77.6
100
1.5
4.2
8.2
ZSM-5
Beta
1:1:0
1:1:0
1:1:1
7.8
Zn/Beta
Fe/Beta
Cu/Beta
Mn/Beta
Ni/Beta
1:1:0
1:1:0
1:1:0
1:1:0
52.8
64.8
35.4
28.6
83.1
1:1:0
Reaction condition: the mixtures of ADA(1 mmol) and excessive aniline (4 mmol) react for 5 min
a
b
under continuous microwave irradiation. the weight ratio of ADA:catalyst:H2O; conversion of
ADA; c quinoline determined by GC; based on ADA.

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Table 2 The reaction of ADA with different substituted aniline
anilines
Product
Yield of quinolines (%)
58.4
41.3
66.8
25.8
19.4
31.3
65.3
57.2
32.1
27.9
29.6
31.5
Reaction condition: the mixtures of ADA (1 mmol) and anilines (4 mmol) react for 5
min under continuous microwave irradiation over Ni/Beta catalyst; the weight ratio of
ADA:catalyst= 1:1.

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Figure captions
Fig. 1 The effect of microwave time for quinoline yield over different
catalysts.
Fig. 2 the effect of reaction time for product distribution over Beta(I) and
Ni/Beta(II) catalyst.

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100
Ni/Beta
80
60
40
Beta
20
0
0
5
10
15
20
25
30
35
40
Reaction time /min
Fig. 1 The effect of microwave time for quinoline yield over different catalysts
Reaction condition: the mixtures of ADA(1 mmol) and excessive aniline (4 mmol) react for under
continuous microwave irradiation.

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I
100
80
60
40
20
0
I
100
Conversion of ADA
Yield of 2HQ
Yield of 4HQ
Yield of Q
80
60
40
20
0
Yield of 2HQ
Yield of 4HQ
Yield of Q
Conversion of ADA
5
10
20
30
40
1
3
5
10
Reaction time/min
Reaction time /min
Fig. 2 the effect of reaction time for product distribution over Beta(I) and Ni/Beta(II) catalyst
Reaction condition: the mixtures of ADA(1 mmol) and excessive aniline (4 mmol) react for under
continuous microwave irradiation. Q, 2HQ and 4HQ correspond to quinoline, dihydroquinoline
and tetrahydroquinoline, respectively.

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Scheme captions
Scheme 1. The plausible reaction pathway to form quinoline from
aniline and ADA under microwave irradiation.

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Graphical Abstract

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Highlights

A facile and solvent-free microwave-assisted approach to quinoline was
developed.



An mild, ecofriendly and low-cost zeolite-base catalyst of Ni/Beta was employed.
the 83% yield of quinoline was obtained at a short microwave time.
The addition of Ni significantly accelerated dehydrogenation rate during reaction.

Graphics Abstract

Figure 1

Figure 2