Study on the reaction between bisphenol A and dimethyl carbonate over organotin oxide

Article abstract of DOI:10.1016/j.catcom.2012.12.017

Organotin oxide was used to catalyze the reaction between BPA (bisphenol A) and DMC (dimethyl carbonate), and Ph₂SnO (diphenyltin oxide) displays the excellent catalytic performance in transesterification and O-methylation. However, Bu₂SnO (dibutyltin oxide), (PhCH ₂)₂SnO (dibenzyltin oxide) and (C₆H ₁₁)₂SnO (dicyclohexyltin oxide) exhibited weaker catalytic activity but higher selectivity for C-methylation product formation. The π-π function between Ph₂SnO and BPA provided more chances for their interaction, and π-d interaction between phenyl ring and Sn resulted in catalyst having higher activity in transesterification and O-methylation. O-methylation product formation over Ph₂SnO comes from transesterification product decomposition not from direct methylation of BPA with DMC.

Full text of DOI:10.1016/j.catcom.2012.12.017

Study on the reaction between bisphenol A and dimethyl carbonate over
organotin oxide
Xiaolong He, Zhenhuan Li, Kunmei Su, Bowen Cheng, Jun Ming
PII:
DOI:
Reference:
S1566-7367(12)00474-8
doi: 10.1016/j.catcom.2012.12.017
CATCOM 3369
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
9 October 2012
16 December 2012
17 December 2012
Please cite this article as: Xiaolong He, Zhenhuan Li, Kunmei Su, Bowen Cheng, Jun
Ming, Study on the reaction between bisphenol A and dimethyl carbonate over organotin
oxide, Catalysis Communications (2012), doi: 10.1016/j.catcom.2012.12.017
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ACCEPTED MANUSCRIPT
Study on the reaction between bisphenol A and dimethyl
carbonate over organotin oxide
Xiaolong He1, Zhenhuan Li1*, Kunmei Su2, Bowen Cheng1*, Jun Ming1
1School of Materials Science and Engineering, The State Key Laboratory of Hollow Fiber
Membrane Materials and Processes, Tianjin Polytechnic University, 300160 Tianjin, China.
2School of environment Science and Chemisty Engineering, Tianjin Polytechnic University,
300160 Tianjin, China.
*
Corresponding author: School of Materials and Chemical Engineering, Tianjin Polytechnic
University, Tianjin, 300160, China
Tel: +86 022 83955358; Fax: +86 022 83955055
E-mail address: Zhenhuanli1975@yahoo.com.cn; lizhenhuan@tjpu.edu.cn.
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Abstract
Organotin oxide was used to catalyze the reaction between BPA (bisphenol A)
and DMC (dimethyl carbonate), and Ph2SnO (diphenyltin oxide) displays the
excellent catalytic performance in transesterification and O-methylation. However,
Bu2SnO (dibutyltin oxide), (PhCH2)2SnO (dibenzyltin oxide) and (C6H11)2SnO
(dicyclohexyltin oxide) exhibited weaker catalytic activity but higher selectivity for
C-methylation product formation. The π-π function between Ph2SnO and BPA
provided more chances for their interaction, and π-d interaction between phenyl ring
and Sn resulted in catalyst having higher activity in transesterification and
O-methylation. O-methylation product formation over Ph2SnO comes from
transesterification product decomposition not from direct methylation of BPA with
DMC.
Keywords: Transesterification; Methylation; Organotin oxide; Dimethyl carbonate;
Bisphenol A.
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1 Introduction
Bisphenol-A polycarbonate (PC) is one of the most widely used engineering
thermoplastics because of its excellent properties such as high-impact strength, heat
resistance, flame retardancy, dimensional stability, and high optical transparency [1].
PC is often produced by the interfacial polycondensation of BPA and phosgene. In an
attempt to devise a phosgene free PC synthesis process, diphenyl carbonate (DPC)
[2–5], CO [6–8] and DMC [9–11] were used as carbonylating agents to replace
phosgene. The transesterification of DMC with BPA is of significant interest as a green
route to aromatic polycarbonates. Shaikh et al [12, 13] had synthesized the
bis-methylcarbonate
of
bisphenol-A
(BMBPA)
and
found
BMBPA
melt-polycondensation to achieve high molecular weight PC. Therefore, the selective
synthesis of BMBPA from BPA and DMC has become particularly important.
However, BMBPA synthesis from DMC and BPA suffers from low yield and
selectivity even at elevated temperature due to a thermodynamically unfavorable
process. Apparently, In the PC synthesis by the transesterification of DMC with BPA,
the major challenge subjects were to improved target compound selectivity, and the
byproducts formed from O-methylation of BPA or C-methylation of BPA with DMC
must be eliminated because the methylation byproducts especially C-methylation
hindered BMBPA polycondensation [14-17] (see scheme 1). Organotin catalyst had
been considered as fine catalyst for transesterification [18], but the design of new
active catalytic systems was prerequisite to promote BMBPA synthesis. BMBPA
synthesis from BPA and DMC was often catalyzed by Lewis acid catalysts, for
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example, TiO2/SBA-15[14], TiO2/SiO2 [15], (Bu2SnCl)2O [16], Bu2SnO and titanium
alkoxides [16]. The development of heterogeneous catalysts with better performance
was highly desirable in view of regeneration and separation. The transesterification of
BPA with DMC can be promoted by TiO2/SBA-15 [14, 19], however, the yield and
selectivity of BMBPA over TiO2/SBA-15 were still far from satisfaction in
comparison with those over homogeneous organotin catalyst. Li et al [17] found that
heterogeneous organotin modified SBA-15 can promote BMBPA synthesis, but the
methylation is still an important side-reaction. Because the synthetic procedure for
BMBPA is a thermodynamically unfavorable process and the high reaction temperature
will result in methylation byproduct formation, apparently, it is a challenge problem to
selectively promote the transesterification of BPA with DMC. Apparently, in order to
keep BPA and DMC from methylation, the methylation reaction between BPA and
DMC need to be well studied over organotin oxide catalyst, which provides deeper
insights into the methylation by-product formation process.
Herein, we introduced a several organotin oxide to selectively catalyze the
reaction between BPA and DMC. Diphenyltin oxide displays the excellent catalytic
o
performance in the selective transesterification even at 120 C, however, it can
o
catalyze the O-methylation product formation at high reaction temperature (>180 C).
Compared to diphenyltin oxide, dialkyltin oxide such as Bu2SnO, (PhCH2)2SnO and
(C6H11)2SnO showed a better activity for direct C-methylation. In order to provide
deeper insights into the reaction process, different reaction parameters were studied.
2. Experiment
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2.1. Chemical Reagents
DMC (Tianjin Chemical Reagent Research Institute) was fractionally distilled
and stored over 4A molecular sieve. BPA and other chemical reagents were AR grade
and used as received from local manufactures without further purification. Ph2SnO
and Bu2SnO were purchased from Sigma-Aldrich.
2.2. Phenyl tinoxide preparation
(PhCH2)2SnO and (C6H11)2SnO were synthesized from Grignard reagents and
stannic tetrachloride at certain mole ratio in tandem with hydroxylation in presence of
NaOH.
2.3. Characterization
Fourier transform infrared spectra (FT-IR) of the samples were measured through
a FTIR TENSOR 37 (BRUKER Corporation, Germany) operated by Attenuated Total
Reflectance (ATR) in the wavenumber range of 4000-500 cm-1. Quantitative analysis
was carried on a gas chromatograph (PERSEE GC1100 with a FID detector,
HP-5/DB-5 capillary column) with cetane as interior standard. The HPLC analyses
were carried out by a reverse-phase method on a Waters 2690 separation module
(Waters Associates, Milford, MA). As an UV detector, a Waters 2487 Dual
Absorbance Detector was used at the wavelength of UV 254nm. The reverse-phase
C18 column was Waters Lichrosorb adjusted with a gradient mode of CH3OH and
water from 80/20 to isocratic CH3OH.
2.4. Reaction procedure
Reactions were carried out in two methods, at ambient pressure with continuous
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removal of by-producing methanol and under pressured condition without removal of
by-producing methanol. Ambient pressure reactions were carried out in a four neck
flask which was equipped with a thermometer, a nitrogen inlet, a dropping funnel and
a fractionating column connected to a liquid dividing head. BPA and catalyst were
charged into a flask under nitrogen atmosphere. During the reaction, a distillate of
DMC and methanol was collected slowly in a receiver flask. Pressured reaction was
carried out in polytetrafluoroethylene reaction kettles. After the reaction finished, the
mixture was cooled and analyzed.
3. Results and Discussion
3.1. Characterization of organotin oxide catalysts
FT-IR spectra of the samples are presented in Fig.1. The characteristic absorption
band at 1472 cm-1 was caused by stretching vibration of benzene skeleton, and the
bending vibration at 698 cm-1 was caused by =C-H of benzene. The absorption bands
for Sn=O bond stretching vibration occurred at 1072cm-1. 2920 cm-1 was attributed
the presence of CH2. The weight loss was carried out under an air atmosphere in
o
muffle furnace at 900 C for 3 h. (PhCH2)2SnO, (C6H11)2SnO and Ph2SnO catalysts
exhibited 48.7%, 52.3% and 55.6% SnO2 residue at 900 oC. Those data match very
well with the theory value 47.6%, 50.2% and 55.2%.
3.2 The organotin oxide catalyzed the reaction between DMC and BPA
The catalytic performance of organotin catalysts was systematically summarized
o
in Table. 1. When reactions were carried out at 120 C at ambient pressure with
continuous removal of by-producing methanol, BPA conversion over Ph2SnO reached
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33.7%, the selectivity of transesterification products achieved 100%, and no
methylation byproducts were detected. Although transesterification was a
thermodynamically unfavorable process, the high temperature was still benign to
DMBPA synthesis [13]. When reaction was carried out at 180 oC over Ph2SnO at
ambient pressure, BPA conversion came up to 51.9%. But the selectivity of
transesterification products declined to 76.3%, and O-methylation byproduct
o
selectivity reached 23.2%. If reactions were carried out at 220 C over Ph2SnO under
pressured condition without removal of by-producing methanol, the yields of
O-methylation products came up to 95.5-97.5%, however, nearly no MMBPA and
C-methylation products were detected. Contrary to expectation, (C4H9)2Sn=O,
(C6H11)2SnO and (PhCH2)2SnO show lower activity in BPA conversion, and much
more C-methylation byproducts appeared. On the basis of those studies, we can
hypothesize that the aromic ring appearance in organotin might have π-π function
with BPA, which provided more chances for phenolic hydroxyl group and Sn=O bond
to contact. Most importantly, phenyl ring in Ph2SnO has a strong π-d interaction with
Sn. The positive Sn cation has higher ability to activate DMC and well promotes the
reaction of BPA with DMC. Additionally, Ph2SnO can be precipitated from reaction
mixture by adding CH3OH, and the refreshed catalytic can be recycled without loss in
activity.
3.3 Effect of temperature on transesterification and methylation
Ph2SnO can catalyze transesterification at low temperature, but much more
O-methylation byproduct formed at high temperature, therefore the O-methylation
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byproduct formation mechanism need to be explored. Herein, temperature effects on
reaction selectivity were investigated under pressured condition without removal of
by-producing methanol. As obviously exhibited in Fig.2, temperature plays a great
role on product distribution and BPA conversion. The selectivity of MMBPA declined
from 66.9 to 0.5% as reaction temperature rising from 160 to 240 oC, but MBPA ether
and DMBPA ether increased to 82.6% and 13.9%. In addition, elevating reaction
temperature can well inhibit C-methylation of BPA. Those results suggested that high
temperature was benign to MBPA ether and DMBPA ether formation.
3.4 Effect of reaction time on transesterification and methylation
Transesterification product disappearance process and O-methylation byproduct
formation mechanism need to be further explored. Here, effects of reaction time on
product selectivity were studied, and results were showed in Fig.3. When reaction
time increased from 6 to16h, BPA conversion increases from 72.7 to 100%, and
MBPA ether and DMBPA ether increased from 22.2% and 4.8% to 82.0% and 13.7%,
however, MMBPA selectivity declined from 70.0 to 4.9%. Base on those results, we
confirmed that O-methylation byproducts mainly come from MMBPA and DMBPA
decomposition not from direct O-methylation of BPA with DMC (see scheme 2).
3.5 Effect of Ph2SnO catalyst usage amount on transesterification and methylation
A series of reactions using different catalyst usages were conducted, and the
results were showed in Fig.4. Ph2SnO usage plays a great role on BPA conversion and
product distribution. Conversion of BPA increased gradually with the rising amount of
catalyst. When catalyst usage was 0.05g, BPA conversion and MBPA ether yield are
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33.9% and 77.2%, and much more transesterification product MMBPA existence
whose selectivity reached 10.6%. The selectivity of MBPA ether reached as high as
90.8% when Ph2SnO dosage was 0.1g, but BPA conversion was 47.8% and no
MMBPA was detected. This result implied that MMBPA or DMBPA decomposition
rate is high than the transesterification rate of BPA with DMC. The similar results
were obtained with the increase of catalyst dosage from 0.3 to 0.4g. Much more
catalyst was loaded, the high selectivity of DMBPA ether achieved, and the selectivity
of DMBPA ether increased to 25.0% when Ph2SnO dosage was 0.4g.
4 Conclusions
Ph2SnO displayed high activity to catalyze transesterification and O-methylation,
and MBPA ether and DMBPA ether mainly come from MMBPA and DMBPA
decomposition not from direct O-methylation of BPA with DMC. Alkyltin oxide, such
as (C4H9)2Sn=O, (C6H11)2SnO and (PhCH2)2SnO, shows lower activity for BPA
conversion but higher selectivity for C-methylation product formation. The π-d effect
in phenyltin oxide and π-π function between BPA and Ph2SnO promote the reaction of
BPA with DMC, and π-d interaction between phenyl ring and Sn result in Sn having
higher activity in the transesterification of BPA with DPC and decomposition of
MMBPA or DMBPA into MBPA ether or DMBPA ether. However, transesterification
products are more stable in presence of alkyltin oxide.
Acknowledgments:
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The authors are grateful for the financial support of the National and Tianjin
Natural Science Foundation of China (nos. 21006071, 30900092 and
12JCZDJC29800).
References
[1] D.Freitag, U.Grico, P. R. Muller, W. Nourvertne, in: H. F. Mark, et al. (Eds.), in
Encyclopedia of Polymer Science and Engineering, Vol. 11; John Wiley: New
York, 1987, pp. 649.
[2] S. Fukuoka, M. Kawamura, K. Komiya, M. Tojo, H. Hachiya, K. Hasegawa, M.
Aminaka, H. Okamoto, I. Fukawa, S. Konno, Green Chem. 5(2003)497.
[3] E. Turska, A.M. Wrobel, Polymers 11(1970)415.
[4] Y. Kim, K.Y. Choi, T.A. Chamberlin, Ind. Eng. Chem. Res. 31(1992)2118.
[5] U. Curtius, L. Bottoenbruch, H. Schnell, U.S. Patent 3,442,854 (1969).
[6] M. Goyal, R. Nagahata, J. Sugiyama, M. Asai, M. Ueda, K. Takeuchi, Polymers
40(1999)3237
[7] I.I. Moiseev, M.N. Vargaftik, T.V. Chernysheva, T.A. Stromnova, A.E. Gekhman,
G.A.Tsirkov, A.M. Makhlina, J. Mol. Catal. A 108(1996)77.
[8] H.Y. Song, E.D. Park, J.S. Lee, J. Mol. Catal. A 154(2000)243.
[9] V. Pokharkar, S. Sivaram, Polymers 36(1995)4851.
[10] M.M. Deshpande, A.S. Jadhav, A.A. Gunari, J.C. Sehra, S. Sivaram, J. Polym.
Sci., Part A: Polym. Chem. 33(1995)701.
[11] D.A. Bolon, J.E. Hallgren, U.S. Patent 4,452,968 (1984).
10

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[12] A. G. Shaikh, S. Sivaram, C. Puglisi, F. Samperi, G. Monotando, Polym Bull.
32(1994)427.
[13] A. G. Shaikh, S. Sivaram, Ind. Eng. Chem. Res. 31(1992)1167.
[14] K.M Su, Z.H Li, B.W. Cheng, K. liao, D.X. Shen, Y.F. Wang, J. Mol. Catal. A,
315(2010)60.
[15] W.B. Kim, Y.G. Kim, J.S. Lee, J. Appl. Polym. Sci. 86(2002)937.
[16] O. Haba, I. Itakura, M. Ueda, S. Kuze, J. Polym. Sci. A 37(1999)2087.
[17] Z.H. Li, K.M. Su, B.W. Cheng, J. Ming, L. Zhang, Y.C. Xu, Catal. Commun.
12(2011)932.
[18] A.G. Shaikh, Chem. Rev. 96(1996)951.
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Captions
Fig .1 FT-IR spectra of organotin oxide catalysts
Fig.2. Effect of temperature on yield (5gBPA, 50ml DMC, 0.3g ph2SnO and16h)
Fig.3 Effect of reaction time on product distribution and BPA conversion (5gBPA、
50ml DMC、0.3g Ph4Sn3O4、220 oC)
Fig.4 Effect of Ph2SnO catalyst amount on reaction (5g BPA、50ml DMC、220 oC、
16h)
Scheme 1 The product distribution of dimethyl carbonate (DMC) reaction with
bisphenol-A
Scheme 2 MBPA ether and DMBPA ether come from MMBPA and DMBPA
decomposition not from directing O-methylation of BPA with DMC
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Ph2SnO
( C6H12) SnO
2
( PhCH2) SnO
2
3000 2700 2400 2100 1800 1500 1200 900
Wavenumber (cm-1)
600
Fig .1 FT-IR spectra of organotin oxide catalysts
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100
80
60
40
20
0
Conversion(BPA)
C-methylation
MMBPA
MBPA ether
DMBPA ether
160
180
200
220
240
Reaction temperature (oC)
Fig.2 Effect of temperature on yield (5gBPA, 50ml DMC, 0.3g ph2SnO and16h)
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100
80
60
40
20
0
BPA conversion
Ortho methylation
MMBPA
MBPA ether
DMBPA ether
4
6
8
10
12
14
16
18
20
22
Reaction time (h)
Fig.3 Effect of reaction time on product distribution and BPA conversion (5gBPA、
50ml DMC、0.3g Ph4Sn3O4、220 oC)
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110
100
90
80
70
60
50
40
30
20
10
0
Conversion(BPA)
C-methylation
MMBPA
MBPA ether
DMBPA ether
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Amount of catalyst
Fig.4. Effect of Ph2SnO catalyst amount on reaction (5g BPA、50ml DMC、220 oC、
16h)
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O
CH3
O
C
O
O
O
OCOCH3
HO
H3CO C
O
C
O
OCH3
OCOCH3
+
H3COCO
+
CH3
n
MMBPA
BMBPA
polymer
Tansesterification
O
+
CH3OCOCH3
BPA
By-products
Methylation
OH
CH3
HO
+
HO
OCH3
OCH3
H3CO
+
C-methylation
MBPA ether
DMBPA ether
Scheme 1 The product distribution of dimethyl carbonate (DMC) reaction with
bisphenol-A
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O
O
O
O
Ph2SnO
OH +
HO
CH3OCOCH3
OCOCH3
HO
+
OCOCH3
H3COCO
160-200 oC
MMBPA
BMBPA
DMC
BPA
180-240 oC
CO2
DMCor CH3OH
OCH3
+ H3CO
OCH3
HO
DMBPA ether
MBPA ether
Scheme 2 MBPA ether and DMBPA ether come from MMBPA and DMBPA
decomposition not from directing O-methylation of BPA with DMC
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Tab.1 Effects of catalysts on reaction between BPA and DMC
Product distribution (mol %)
Tem
(oC)
Con
Catalyst
MBPA DMBPA
(%)
MMBPA BMBPA C-Me
ether
ether
aPh2SnO
aPh2SnO
120
180
33.7
51.9
89.3
71.1
10.7
5.2
----
0.5
----
----
----
23.2
bPh2SnO
220
220
220
220
220
220
220
99.5
65.5
47.8
99.1
56.1
74.7
68.8
0.7
-----
0.1
----
----
----
----
----
----
----
1.8
2.8
62.4
88.1
90.8
66.2
8.8
35.1
9.2
bPh2SnO (0.2)
bPh2SnO (0.1)
bR-Ph2SnO
2.0
7.1
0.9
2.0
31.8
8.5
bBu2Sn=O
58.9
36.5
30.8
23.8
36.1
46.9
b(PhCH2)2SnO
b(C6H11)2SnO
16.8
16.7
10.6
5.6
Reaction conditions: 5g BPA, 50ml DMC, 0.3 g catalyst, 16 h. 0.2 and 0.1 indicated
a
0.2 g and 0.1 g catalyst usage. indicated that reactions were carried out at ambient
pressure with continuous removal of by-producing methanol. b indicated that reactions
were carried out under pressured condition without removal of by-producing
methanol. R-Ph2SnO was the refreshed catalyst. C-Me indicated the methylation at
phenyl ring. Tem and Con indicated Temperature and Conversion.
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O
O
O
O
Ph2SnO
OH +
HO
CH3OCOCH3
OCOCH3
HO
+
OCOCH3
H3COCO
160-200 oC
MMBPA
BMBPA
DMC
BPA
180-240 oC
CO2
DMCor CH3OH
OCH3
+ H3CO
OCH3
HO
DMBPA ether
MBPA ether
Graphical abstract
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Highlights
Ph2SnO selectively catalyzes O-methylation product formation from BPA and
DMC.
Alkyltin oxide catalyzes C-methylation of BPA with DMC.
Ph2SnO catalyzes transesterification products decomposition into O-methylation
products.
Transesterification products are more stable over alkyltin oxide.
21