Synthesis of 5-tert-butyl-1,2,3-trimethylbenzene catalyzed by [Et3NH]Cl–AlCl3

Article abstract of DOI:10.1134/S1070363216050303

Common Lewis acids and Lewis acidic ionic liquid catalysts were applied in the synthesis of 5-tert-butyl-1,2,3-trimethylbenzene from 1,2,3-trimethylbenzene and 2-chloro-2-methylpropane, where [Et₃NH]Cl–AlCl₃ demonstrated the most promising catalytic potential. The effects of reaction time, temperature, catalyst composition and dosage have been systematically studied in the presence of [Et3NH]Cl–AlCl3. The maximum selectivity of 90.32% was achieved upon heating at 10°C for 5 h with a mass fraction of [Et₃NH]Cl–AlCl₃ to 1,2,3-trimethylbenzene of 10%. Activity of the ionic liquid catalyst remained high after several cycles.

Full text of DOI:10.1134/S1070363216050303

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 5, pp. 1163–1166. © Pleiades Publishing, Ltd., 2016.
Synthesis of 5-tert-Butyl-1,2,3-trimethylbenzene Catalyzed
1
by [Et NH]Cl–AlCl
3
3
a,b
a,b
a–c
a,b
c
L. Zhang , Y. Huang , B. Jiang , Y. Sun , and H. Ren
a
School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072 China
e-mail: zhanglvh@tju.edu.cn
b
Collaborative Innovation Center of Chemical Science and Engineering,
Tianjin University, Tianjin, 300072 China
c
National Engineering Research Centre of Distillation Technology,
Tianjin University, Tianjin, 300072 China
Received December 17, 2015
Abstract—Common Lewis acids and Lewis acidic ionic liquid catalysts were applied in the synthesis of 5-tert-
butyl-1,2,3-trimethylbenzene from 1,2,3-trimethylbenzene and 2-chloro-2-methylpropane, where [Et NH]Cl–
AlCl demonstrated the most promising catalytic potential. The effects of reaction time, temperature, catalyst
composition and dosage have been systematically studied in the presence of [Et NH]Cl–AlCl . The maximum
selectivity of 90.32% was achieved upon heating at 10°C for 5 h with a mass fraction of [Et NH]Cl–AlCl to
,2,3-trimethylbenzene of 10%. Activity of the ionic liquid catalyst remained high after several cycles.
3
3
3
3
3
3
1
Keywords: [Et NH]Cl–AlCl , alkylation, 1,2,3-trimethylbenzene, ionic liquid
3
3
DOI: 10.1134/S1070363216050303
INTRODUCTION
several minutes, retarding the reaction agitation. With
the molar ratio 3 : 1 conversion was total and
selectivity was 85.02%. The latter was close to the
selectivity observed with the molar ratio 2 : 1. Taking
in consideration all factors the molar ratio 2 : 1 was
considered as the most efficient.
1
,2,3-Trimethylbenzene is an important starting
chemical for producing 5-tert-butyl-1,2,3-trimethyl-
benzene, which is mainly used in the synthesis of musk
tibetene [1, 2] (Scheme 1).
Ionic liquids demonstrate unique chemical and
physical properties and have been widely used as
catalysts, solvents, extractants, adsorbents, and per-
At the following step common Lewis acid and
Lewis acidic ionic liquid were introduced in the
synthesis of 5-tert-butyl-1,2,3-trimethylbenzene (Table 1).
AlCl and FeCl demonstrated excellent catalytic per-
formance additives [3–6]. Traditionally AlCl acts as
3
3
3
the catalyst in the reaction of 1,2,3-trimethylbenzene
with 2-chloro-2-methylpropane [1, 2, 7, 8]. In the
current study common Lewis acids and some Lewis
acidic ILs were introduced in the alkylation process.
formance giving reaction conversion ca 90% and
selectivity up to 84.38% and 81.92%, respectively.
[
Et NH]Cl–AlCl Was determined to be the most
Scheme 1. Synthesis of 5-tert-butyl-1,2,3-trimethylbenzene.
3
3
efficient catalyst under various conditions.
CH3
RESULTS AND DISCUSSION
H C
CH + (CH ) CCl
3
3
3 3
Alkylation with different catalysts. Influence of
molar ratio of reactants upon AlCl3 catalysis is
presented in Table 1. At the molar ratio of 2-chloro-2-
methylpropane to 1,2,3-trimethylbenzene 1 : 1 or 1.5 : 1,
the reactor was filled with pale yellow filaments after
CH
3
Catalyst
H C
CH + HCl
3
3
1
The text was submitted by the authors in English.
C(CH )
3 3
1
163

1
164
ZHANG et al.
a
Table 1. Effect of molar ratio and different catalysts on alkylation
b
c
c
Run no.
Catalyst
Molar ratio
1 : 1
Dosage, %
Conversion , %
Selectivity , %
1
2
3
4
5
6
7
8
9
AlCl
AlCl
AlCl
AlCl
AlCl
3
2
2
2
2
2
2
2
2
2
2
5
–
–
3
3
3
3
1.5 : 1
2 : 1
–
–
99.09
100.00
99.09
0.00
84.38
85.02
84.38
0.00
81.92
0.00
0.00
63.48
3 : 1
2 : 1
CuCl
FeCl
[bmim]–AlCl
[bmim]–BF
2
2 : 1
3
2 : 1
99.59
100.00
98.77
49.98
99.81
d
3
2 : 1
4
2 : 1
e
1
1
0
1
[Et
3
3
NH]Cl–AlCl
3
3
2 : 1
[Et
NH]Cl–AlCl
2 : 1
88.39
a
b
c
Reaction condition: T = 10°C, t = 5 h. Molar ratio refers to 2-chloro-2-methylpropane to 1,2,3-trimethylbenzene. 1,2,3-Trimethyl-
d
e
3
benzene is the key component. Bmim refers to 1-butyl-3-methylimidazolium. Molar ratio of n(AlCl )/n([bmim]) = 2.
However, it was difficult to separate the products from
reaction (Table 2). The higher content of aluminum
chloride contributed to the improvement of the
reaction selectivity. When n(AlCl )/n([Et NH]Cl) was
the catalysts. CuCl Demonstrated no catalytic activity.
2
The reaction conversion under the action of [bmim]-
AlCl and [bmim]–BF was very high along with poor
3
3
1 : 1, the ionic liquid demonstrated no catalytic
3
4
selectivity. Application of [Et NH]Cl–AlCl (2%) as
activity. The higher molar ratio of AlCl (1.3 : 1, 1.5 :
3
3
3
the catalyst in the reaction gave conversion 49.98%
and selectivity 63.48%. Increase of the IL quantity to
1, 1.7 : 1 and 2 : 1) led to the reaction conversion close
to 100% [9,10] and higher selectivity which was
maximum (90.32%) at n(AlCl )/n([Et NH]Cl) at 2 : 1.
5
% conversion and selectivity improved significantly
3
3
which could be caused by the increase of quantity of
acid sites. Therefore, more specific and detailed
research had been performed using [Et NH]Cl–AlCl .
Effect of IL amount on alkylation. Influence of
AlCl content in the ionic liquid is presented in Table 3.
3
3
3
Increase in the reaction selectivity could be explained
by the fact that the quantity of acid sites was increased
with the addition of IL. The reaction rate was high
with 10% IL catalysis. Further increase of ILs amount
made the reaction uncontrollable, and the temperature
Effect of composition of IL on alkylation. Acid
strength of various ILs greatly affects their catalytic
activity. In the study different molar ratio of ionic
liquid had been used in catalysis of the alkylation
a
a
Table 2. Effect of composition of IL on alkylation
Table 3. Effect of IL quantity on alkylation
n(AlCl
3
)/n([Et
3
NH]Cl)
Conversion, % Selectivity, %
Dosage, %
Conversion, %
49.98
Selectivity, %
63.48
1
1
1
1
2
.0
.3
.5
.7
.0
0
100
100
100
100
0.00
2
5
86.52
86.76
89.14
90.32
99.91
88.39
1
1
2
0
5
0
100.00
90.32
100.00
80.58
100.00
76.75
a
a
Reaction conditions: molar ratio 2-chloro-2-methylpropane : 1,2,3-
trimethylbenzene = 2 : 1, 10% [Et NH]Cl–AlCl , 5 h, 10°C.
Reaction conditions: molar ratio of 2-chloro-2-methylpropane :
1,2,3-trimethylbenzene = 2 : 1, 5 h, 10°C.
3
3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 5 2016

SYNTHESIS OF 5-tert-BUTYL-1,2,3-TRIMETHYLBENZENE
1165
a
a
Table 4. Effect of temperature on alkylation
Table 5. Effect of reaction time on alkylation
Time, h
Conversion, %
99.91
Selectivity, %
86.75
T, °C
Conversion, %
Selectivity, %
1
2
3
4
5
6
2
5
99.94
100.00
100.00
100.00
100.00
88.04
88.67
90.32
88.20
86.33
99.98
89.38
100.00
89.53
1
1
2
0
5
0
100.00
89.69
100.00
90.32
100.00
90.36
a
a
Reaction conditions: molar ratio of 2-chloro-2-methylpropane :
,2,3-trimethylbenzene = 2 : 1, 10% [Et NH]Cl–AlCl , 5 h.
Reaction conditions: molar ratio of 2-chloro-2-methylpropane :
1,2,3-trimethylbenzene = 2 : 1, 10% [Et NH]Cl–AlCl , 10°C.
1
3
3
3
3
would rise leading to side reactions. It was concluded
that 10% of the IL in the alkylation system would have
sufficient acid sties for the reaction.
ILs were prepared by slow addition of the desired
amount of AlCl to TEA salt in heptane under the
3
atmosphere of dry N . Light brown liquid layer
2
appeared upon storage at room temperature for 0.5 h.
The lower liquid lawer was transferred to rotary eva-
porater to purify the ionic liquid which was stirred for
Effect of reaction temperature on alkylation. The
reaction conversion was ca 100% in the temperature
range from 0 to 20°C. The reaction selectivity
demonstrated an upward trend at temperature lower
than 10°C and a downward trend at that higher than
2
h at 80°C. Color of the ILs varied from brown to
black.
1
0°C, which was comparable with the effect of high
quantity of IL. Maximum reaction selectivity was
0.32% at 10°C. High temperature induced side
1-Butyl-3-methylimidazolium-AlCl and 1-butyl-3-
methylimidazolium-BF4 were purchased from
Shanghai Cheng Jie Chemical Co. LTD.
3
9
reactions (Table 4).
Alkylation reaction. Alkylation experiments were
carried out in a 50 mL reactor. A low temperature
super thermostat bath was used to control the reaction
temperature with ethanol as a working fluid. The
catalysts and reactants were added in the desired ratio.
When metal chlorides acted as the catalytic media, the
alkylate needed to be neutralized with a saturated
Na CO , washed with NaCl, and then with water.
Effect of reaction time on alkylation. According
to the experimental data (Table 5) the reaction
conversion was close to 100% after 1 h of the process.
The reaction selectivity gradually increased with the
extension of time and reached 90.32% after 5 h and
then remained stable indicating the reaction equilib-
rium point. Longer reaction time would result in more
side reactions and lower reaction selectivity.
2
3
Upon drying with anhydrous Na SO the products
2
4
were instantly analyzed by a GC-MS Agilent
890/5975C-Gas Chromatographer (GC)/Mass
Selective Detector (MSD); HP-5, MS column, 30 m ×
Reusability of the catalyst. Reusability of
7
[
(
Et NH]Cl–AlCl catalyst was studied in a batch mode
3 3
Table 6). Separated with a separation funnel IL
catalyst without further treatment was used again in the
alkylation of 1,2,3-trimethylbenzene under optimum
reaction conditions. Selectivity and conversion of the
process remained nearly the same over the first four
runs and dropped a little in the fifth run. Probably
a
Table 6. Reuse of ionic liquid in the alkylation reaction
Time, h
Conversion, %
100.00
Selectivity, %
90.32
1
2
3
4
5
hydrolysis of AlCl in the ionic liquid could lead to the
3
100.00
90.30
catalyst deactivation [11, 12].
100.00
90.01
EXPERIMENTAL
100.00
89.93
Preparation of ionic liquid. Triethylamine
hydrochloride-aluminum chloride were synthesized
according to the methods reported earlier [13, 14]. The
99.98
89.87
a
Reaction conditions: molar ratio of 2-chloro-2-methylpropane :
1,2,3-trimethylbenzene = 2 : 1, 10% [Et NH]Cl–AlCl , 10°C.
3
3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 5 2016

1
166
ZHANG et al.
2
2
50 μm i.d. × 0.25 μm 120°C–temperature rising
0°C/min–280°.
j.issn:1003-9015.2000.06.015.
3. Boon, J.A., Levisky, J.A., Pflug, J.L., and Wilkes, J.S.,
Org. Process. Res. Dev., 1986, vol. 51, no. 4, p. 480.
DOI: 10.1021/jo00354a013.
CONCLUSIONS
Alkylation of 1,2,3-trimethylbenzene with 2-
4
5
6
. Huddleston, J.G. and Rogers, R.D., Chem. Commun.,
1998, vol. 1998, no.16, p. 1765. DOI: 10.1039/A803999B.
chloro-2-methylpropane using different catalysts had
been studied. [Et NH]Cl–AlCl Was determined to be
. Han, X. and Armstrong, D.W., Acc. Chem. Res., 2007,
vol. 40, no. 11, p. 1079. DOI: 10.1021/ar700044y.
3
3
most promising catalytical substitute for AlCl3.
Temperature of the process, ionic liquid composition,
reaction time and amount of IL influenced the reaction
conversion and selectivity. The optimum reaction
conditions were worked out to be: AlCl /[Et NH]Cl
molar ratio of 2.0, reaction time 5h, temperature 10°C,
mass fraction of IL to 1,2,3-trimethylbenzene 10%.
Reusability of the ionic liquid [Et NH]Cl–AlCl
. Huang, M.Y., Wu, J.C., Shieu, F.S., and Lin, J.-J.,
Chem. Commun., 2009, vol. 10, no. 13, p. 1747. DOI:
10.1016/j.catcom.2009.05.030.
7
8
9
. Chauvin, Y., Hirschauer, A., and Olivier, H., J. Mol.
Catal., 1994, vol. 92, no. 2, p. 155. DOI: 10.1016/0304-
5102(94)00065-4.
3
3
. Yin, D., Li, C., Tao, L., Yu, N., Hu, S., and Yin, D.,
J. Mol. Catal., 2006, vol. 245, nos. 1–2, p. 260. DOI:
10.1016/j.molcata.2005.10.010.
3
3
significantly higher than AlCl and its catalytic activity
remained high after four cycles.
3
. Chen, M. and Tang, X., China Pet. Process. Pe., 2014,
vol. 16, no. 1, p. 60. DOI: 10.3969/j.issn.1008-
6234.2014.01.013.
ACKNOWLEDGMENTS
1
1
0. Han, C., Guo, H.L., Xin, X., and Yan, L.W., China Pet.
Process. Pe., 2013, vol. 15, no. 1, p. 54. DOI: 10.3969/
j.issn.1008-6234.2013.01.009.
Thanks for the help provided by Tianjin University
Analysis Center in the course of this work.
1. Dupont, J., de Souza, R.F., and Suarez, S.P.A., Chem.
Rev., 2002, vol. 102, no. 10, p. 3667. DOI: 10.1002/
chin.200303269.
We are also grateful for the financial support from
Tianjin Oceanic Administration R&D Program (no.
1
9-3BC2014-01).
1
1
2. Gordon, C.M., Appl. Catal. A: Gen., 2001, vol. 222,
no. 1, p. 101. DOI: 10.1016/S0926-860X(01)00834-1.
REFERENCES
3. Welton, T., Chem. Rev., 1999, vol. 99, no. 8, p. 2071.
DOI: 10.1002/chin.199946295.
1
. Li, J. and Liu, H.H., GuiZhou Chem. Ind., 2002, vol. 27,
no. 4, p. 41. DOI: 10.3969/j.issn.1008-9411.2002.04.015.
. Ma, R.R., Ma, J.Q., and Li, G.Y., Chinese J. Chem.
Eng., 2000, vol. 14, no. 6, p. 593. DOI: 10.3321/
14. Huang, C.P., Liu, Z.C., Xu, C.M., Chen, B.H., and
Liu, Y.F., Appl. Catal. A: Gen., 2004, vol. 277, nos. 1–2,
p. 41. DOI: 10.1016/j.apcata.2004.08.019.
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 5 2016