Highly selective synthesis of 3-methylindole from glycerol and aniline over Cu/NaY modified by K2O

Article abstract of DOI:10.1016/j.cclet.2013.07.023

The vapor-phase synthesis of 3-methylindole from glycerol and aniline over Cu/NaY modified by K₂O was investigated. The catalysts were characterized by X-ray diffraction (XRD) and the temperature-programmed desorption of ammonia (NH₃-TPD). The effect of the reaction temperature on the activity and selectivity of Cu/NaY-K₂O catalyst was also investigated. The results indicated that the addition of K₂O to Cu/NaY increased the selectivity of the catalyst remarkably because the amount of middle-strong acid sites decreased clearly. The decrease of the reaction temperature was beneficial for the increase of 3-methylindole selectivity. Over Cu/NaY-K₂O, the selectivity of 3-methylindole reached 75% and the yield of the target product was up to 47% at 220 C. A probable catalytic mechanism for the synthesis of 3-methylindole from glycerol and aniline was proposed.

Full text of DOI:10.1016/j.cclet.2013.07.023

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CCLET-2688; No. of Pages 3
Chinese Chemical Letters xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
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Original article
Highly selective synthesis of 3-methylindole from glycerol and aniline
over Cu/NaY modified by K2O
*
Yan-Xi Cui, Li-Dong Sun, Qi Sun, Lei Shi
Institute of Chemistry for Functionalized Materials, Liaoning Normal University, Dalian 116029, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The vapor-phase synthesis of 3-methylindole from glycerol and aniline over Cu/NaY modified by K2O
was investigated. The catalysts were characterized by X-ray diffraction (XRD) and the temperature-
programmed desorption of ammonia (NH3-TPD). The effect of the reaction temperature on the activity
and selectivity of Cu/NaY-K2O catalyst was also investigated. The results indicated that the addition of
K2O to Cu/NaY increased the selectivity of the catalyst remarkably because the amount of middle-strong
acid sites decreased clearly. The decrease of the reaction temperature was beneficial for the increase of 3-
methylindole selectivity. Over Cu/NaY-K2O, the selectivity of 3-methylindole reached 75% and the yield
of the target product was up to 47% at 220 8C. A probable catalytic mechanism for the synthesis of 3-
methylindole from glycerol and aniline was proposed.
Received 26 March 2013
Received in revised form 13 June 2013
Accepted 18 June 2013
Available online xxx
Keywords:
3-Methylindole
Cu/NaY
K2O promoter
Glycerol
ß 2013 Lei Shi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Aniline
1. Introduction
Today, more and more attention focuses on the production of
value-added chemicals from renewable resources such as biomass
3-Methylindole, one of the most important indole derivatives, is
widely used in perfumes and the manufacture of herbicides,
fungicides, dyes, antihypertensive and anticancer medicines, etc.
[1–4]. For many years, the synthesis of 3-methylindole has been an
area of focus for organic chemists, and numerous synthesis
methods have been developed [5,6]. Among them, liquid phase
synthesis can give 3-methylindole in a good yield, however, some
drawbacks existed, such as the use of complicated and expensive
reagents or catalysts, a large number of toxic solvents, heavy
pollution and severe reaction conditions, etc. [7–9], which limit the
further development of 3-methylindole. From economic and
environmental viewpoints, therefore, vapor-phase synthesis of
3-methylindole is now more attractive. Subrahmanyam and co-
workers investigated the vapor-phase synthesis of 3-methylindole
from methanol and indole over Ce/HY catalyst, obtaining a 30%
yield [10]. Campanati et al. reported the synthesis of 3-
methylindole from 1,2-propanediol and aniline over ZrO2/SiO2
catalyst, but the yield of 3-methylindole was only 12% [11].
Recently, our group developed a new approach for the vapor-phase
synthesis of 3-methylindole with glycerol and aniline as reactants
(Scheme 1). Over Cu/SiO2-Al2O3, the yield of 3-methylindole
reached 40% [12].
[13–15]. Glycerol, which comes from biomass, is not only cheap
and abundant, but also known as a green renewable feedstock.
Therefore, the vapor-phase synthesis of 3-methylindole from
glycerol and aniline is a promising route.
Zeolites have attracted increasing interest in the manufacture
of fine chemicals and chemical intermediates owing to their special
features such as the acidity, inherent product selectivity,
commercial availability, non-corrosive and eco-friendly nature,
etc. [16–18]. In this paper, Cu/NaY and the catalyst modified by K2O
were used for the vapor-phase synthesis of 3-methylindole from
glycerol and aniline. XRD and NH3-TPD techniques were used to
reveal the relationship between the structure of catalysts and their
catalytic performances. The effect of reaction temperature was also
investigated. In addition, a probable catalytic mechanism for the
synthesis of 3-methylindole was proposed.
2. Experimental
Cu/NaY catalyst was prepared by incipient wetness impregna-
tion. After impregnating NaY (20–40 mesh) with copper nitrate
aqueous solution for 15 h at room temperature, the material was
dried at 120 8C for 4 h, and then calcined at 500 8C for 4 h to obtain
the catalyst precursor. Cu/NaY-K2O catalyst was prepared by
sequential impregnation. First, NaY support was pre-impregnated
with an aqueous solution of potassium acetate, then dried and
calcined to get NaY-K2O. Afterwards, NaY-K2O was impregnated
with an aqueous solution of copper, followed by drying and
*
Corresponding author.
E-mail address: shilei515@dl.cn (L. Shi).
1001-8417/$ – see front matter ß 2013 Lei Shi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.07.023
Please cite this article in press as: Y.-X. Cui, et al., Highly selective synthesis of 3-methylindole from glycerol and aniline over Cu/NaY
modified by K2O, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.07.023

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Cu sites
Acid sites
HO
OH
OH
Table 1
H2O
2H2O
NH2
OH
,
N
H
The activity and selectivity of Cu/SiO2-Al2O3, Cu/NaY or Cu/NaY-K2O.
O
Catalyst
Glycerol
3-Methylindole
yield (%)
3-Methylindole
selectivity (%)
Acetol
Glycero
3-Methylindole
conversion (%)
Scheme 1. Vapor-phase synthesis of 3-methylindole from glycerol and aniline.
Cu/SiO2-Al2O3
Cu/NaY
72
70
66
40
37
43
56
53
65
Cu/NaY-K2O
Reaction conditions: 240 8C, Aniline:glycerol = 3:1 molar ratio, SV = 1700 hꢀ1
,
calcining to obtain the catalyst precursor of Cu/NaY-K2O, in which
the procedure of impregnating, drying or calcining was the same as
Cu/NaY described above. Prior to the activity test, 3 mL catalyst
precursor was in situ reduced in a mixture of gas composed of N2
(30 mL/min) and H2 (30 mL/min) at 250 8C for 2 h, then cooled to
reaction temperature in 0.5 h and kept at the temperature for
another 0.5 h. Copper loading was 0.9 mmol/g. The amount of K2O
promoter was 0.4 mmol/g.
LHSV = 0.4 hꢀ1, H2 = 10 mL/min, steam = 12 mL/h, N2 = 58 mL/min. The results were
taken at the second hour.
o
X-ray diffraction (XRD) patterns were recorded on a D8
o
Advance X-ray diffractometer with a Cu K
a radiation source at a
c
scan rate of 0.5 8/min in the 2 range of 308–808. The voltage and
u
current were 40 kV and 40 mA, respectively. The temperature-
programmed desorption of ammonia (NH3-TPD) was performed in
a quartz reactor with inside diameter of 6 mm and length of
350 mm. 150 mg of the sample was pretreated at 500 8C for 1 h in a
flow of ultrapure helium gas (35 mL/min) to remove water and
other contaminants from the catalyst and cooled down to 100 8C,
then saturated with ammonia gas at 100 8C. After the sample was
purged with helium gas (35 mL/min) at 100 8C for 2 h to remove
physisorbed ammonia, TPD was carried out from 100 8C to 700 8C
with a temperature ramp of 10 8C/min.
b
a
30
40
50
60
70
80
The catalytic reactions were carried out in a fix-bed continuous
flow glass reactor with inside diameter of 12 mm under
atmospheric pressure. Aniline and glycerol were mixed in a molar
ratio of 3:1. The total space velocity (SV) and liquid hourly space
2θ ( )
Fig. 1. XRD patterns of Cu/SiO2-Al2O3 (a), Cu/NaY (b) and Cu/NaY-K2O (c).
velocity (LHSV) of raw materials were 1700 hꢀ1 and 0.4 hꢀ1
,
respectively. The mixture of reactants was pumped through the
preheater where they were vaporized and then entered into the
reactor with flowing H2 (10 mL/min), steam (12 mL/min) and N2
(58 mL/min). The products were analyzed on a gas chromatograph
with a mass spectrometer (Shimadzu GCMS-QP2010) using a DB-5
capillary column and a gas chromatograph connected to a
hydrogen flame ionization detector (FID-GC, SP-6800 A) using
OV-17 column. The quantitative analysis of the reactants and
products was carried out on the SP-6890A gas chromatograph
equipped with an SE-54 capillary column. 1-Hexyl alcohol was
used as an internal standard.
peak at the lower temperature (<200 8C) was assigned to the weak
acid sites, while the others at the higher temperature (200–450 8C)
corresponded to the middle-strong acid sites [20]. The amount of
the acid sites on the three catalysts decreased in the order of Cu/
SiO2-Al2O3, Cu/NaY and Cu/NaY-K2O. On Cu/SiO2-Al2O3, there were
many weak acid sites and middle-strong acid sites. On Cu/NaY, the
amount of weak acid sites or middle-strong acid sites that
appeared at about 342 8C increased greatly, while the desorption
peak corresponding to the middle-strong acid sites of 232 8C
became very small. On Cu/NaY-K2O, only two desorption peaks
corresponding to weak acid sites and middle-strong acid sites of
3. Results and discussion
Table 1 shows the activity and selectivity of Cu/SiO2-Al2O3, Cu/
NaY or Cu/NaY-K2O. Compared with Cu/SiO2-Al2O3, Cu/NaY
showed lower activity and selectivity. After adding K2O to Cu/
NaY, although the conversion of glycerol decreased, the selectivity
of 3-methylindole increased remarkably, which resulted in the
increase of 3-methylindole yield to 43%.
Fig. 1 illustrated the XRD patterns of Cu/SiO2-Al2O3, Cu/NaY and
Cu/NaY-K2O. A small diffraction peak of copper at 2u of 43.38,
assigned to the (1 1 1) reflection, was observed on Cu/SiO2-Al2O3
[19]. On NaY supported Cu-based catalysts, the intensity of copper
diffraction peaks became stronger and another diffraction peak at
50.58, assigned to the (2 0 0) reflection of copper, was observed.
Moreover, the intensity of copper diffraction peaks on Cu/NaY-K2O
was stronger than that on Cu/NaY, indicating that the addition of
K2O to Cu/NaY was not conducive to the dispersion of copper
particles on the support.
a
c
b
100
150
200
250
300
350
400
450
500
Temperature (ºC)
Fig. 2 showed NH3-TPD profiles of Cu/SiO2-Al2O3, Cu/NaY and
Cu/NaY-K2O. More than two desorption peaks were observed. The
Fig. 2. NH3-TPD profiles of Cu/SiO2-Al2O3 (a), Cu/NaY (b) and Cu/NaY-K2O (c).
Please cite this article in press as: Y.-X. Cui, et al., Highly selective synthesis of 3-methylindole from glycerol and aniline over Cu/NaY
modified by K2O, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.07.023

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Y.-X. Cui et al. / Chinese Chemical Letters xxx (2013) xxx–xxx
3
Table 2
4. Conclusion
Effect of reaction temperature on the activity and selectivity of Cu/NaY-K2O
catalyst.
The catalysts of Cu/NaY and Cu/NaY-K2O were used for the
vapor-phase synthesis of 3-methylindole from glycerol and
aniline. Although K2O did not promote the dispersion of copper
particles on the support, it could decrease the amount of middle-
strong acid sites, as a result, the selectivity of the catalyst increased
significantly. In addition, the decrease of the reaction temperature
was also favorable to the increase of 3-methylindole selectivity.
Over Cu/NaY-K2O, when the temperature was 220 8C, the
selectivity of 3-methylindole reached 75% and the yield of the
target product was up to 47%. A possible mechanism for the
synthesis of 3-methylindole from glycerol and aniline over
zeolites-supported Cu-based catalysts was proposed, in which
acetol was the intermediate to produce 3-methylindole.
Reaction
Glycerol
3-Methylindole
yield (%)
3-Methylindole
selectivity (%)
temperature (8C)
conversion (%)
180
200
220
240
50
55
63
66
39
42
47
43
78
76
75
65
Reaction
LHSV = 0.4 hꢀ1
conditions:
Aniline:glycerol =3:1
molar
ratio,
SV = 1700 hꢀ1
,
, H2 = 10 mL/min, steam = 12 mL/min, N2 = 58 mL/min. The results
were taken at the second hour.
Cu sites
Acid sites
HO
OH
OH
H2O
2H2O
OH
,
N
H
O
NH2
Acknowledgment
Acetol
Glycero
3-Methylindole
Scheme 2. A probable catalytic mechanism for the synthesis of 3-methylindole
We gratefully acknowledge the financial support provided by
the National Natural Science Foundation of China (No. 21173110).
from glycerol and aniline.
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Please cite this article in press as: Y.-X. Cui, et al., Highly selective synthesis of 3-methylindole from glycerol and aniline over Cu/NaY
modified by K2O, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.07.023