Synthesis of unsaturated esters via highly efficient esterification catalyzed by polymer grafted quarternary ammonium salts as triphase catalysts

Article abstract of DOI:10.4067/S0717-97072013000100013

A series of unsaturated esters were prepared via condensation of sodium carboxylates and alkenyl halide under the condition of macroporous polystyrene grafted quarternary ammonium salt as recyclable phase transfer catalyst, NaI as co-catalyst, Cu powder as inhibitor and H2O as solvent. Under optimal conditions, products yields are 78.2～ 96.0%. The catalyst can be convenient recycled and reutilized for about five times without losing its activity obviously.

Full text of DOI:10.4067/S0717-97072013000100013

J. Chil. Chem. Soc., 58, Nº 1 (2013)
SYNTHESIS OF UNSATURATED ESTERS VIA HIGHLY EFFICIENT ESTERIFICATION CATALYZED BY
POLYMER GRAFTED QUARTERNARY AMMONIUM SALTS AS TRIPHASE CATALYSTS
ZHENG YONG LIANG 1*, LI LI WANG2, HUI LIU1, JIN SHUO HUANG1
1 School of Chemical Engeering and Energy, Zhengzhou University, Zhengzhou, China
2 College of Pharmacy, Henan University of Traditional Chinese Medicine, Zhengzhou, China
(Received: March 30, 2012 - Accepted: October 3, 2012)
ABSTRACT
A series of unsaturated esters were prepared via condensation of sodium carboxylates and alkenyl halide under the condition of macroporous polystyrene
grafted quarternary ammonium salt as recyclable phase transfer catalyst, NaI as co-catalyst, Cu powder as inhibitor and H2O as solvent. Under optimal conditions,
products yields are 78.2~ 96.0%. The catalyst can be convenient recycled and reutilized for about five times without losing its activity obviously.
Keywords: green chemistry, triphase catalysis, polymer grafted quarternary ammonium salt, unsaturated ester
acid value and iodine value determination of DAP refer to GB/T1664-95, GB/
T1668-95 and GB1676-81, respectively. All yields refer to isolated products
after purification.
General procedure for preparation of PS grafted quarternary
ammonium salts.
A mixture of 10g PS-CH2Cl, 100mL 1,2-dichloroethane and 40mL ethyl
alcohol was put into a flask equipped with stirring device, reflux condenser and
thermometer. The mixture was heated up to 60ºC for 2h. Quantitative tertiary
amine according to n(Cl): n(tertiary amine)=1:3 was added. Then the mixture
was kept reflux for 24h. After filtering, washing with ethyl alcohol and vacuum
drying, the TC-1~6 were obtained.
INTRODUCTION
Unsaturated esters are a kind of reactive plasticizer, which are important
monomers in the manufacture of resin. At present, they continue to be in great
demand in fields of aerospace, electronics and telecommunication.1-2 Therefore,
the development of new synthesis technology still holds great significance.
In recent years, many efforts have been carried out on the synthesis of
unsaturatedester.Amongvariousapproaches,themostpreferrediscondensation
of alkali metal carboxylate with alkenyl halide. The original condensation
were generally performed under high temperature and pressure, which was
uneconomical and unsafe.3-4 Though some literatures reported synthesis can
be carried in high boiling solvents, such as xylene, chlorobenzene and DMSO,
at atmospheric pressure, solvents had to be used in large quantities, which
caused serious pollution. 5-7 In order to eliminate the factor of environment
unfriendly, chemists developed a new green synthesis process using water as
solvent to prepare unsaturated ester in the presence of phase transfer catalyst.
General procedure for preparation of unsaturated esters
A mixture of 0.1mol carboxylate(mass=0.1M), 2.0g TC-1~6, 0.75gNaI,
0.05gCu and 20mL H2O was put into a flask equipped with stirring device,
reflux condenser, thermometer and dropping funnel. The mixture was heated
up to 35~40 ℃ for 1h. Then quantitative allyl chloride according to n(Cl):
n(COONa)=2:1 was added dropwise during 2h. After refluxing for 2~4h, the
excess of allyl chloride was distilled off. The reaction mixture was cooled to
room temperature and filtered out quaternary ammonium salts and Cu powder.
Then, organic layer was separated, washed with water, and dried overnight
with MgSO4. The crude product was purified by vacuum distillation in presence
of high boiling point solvent or by a silica-gel column chlomatography with
petroleum ether and EtOAc. Products were obtained in excellent yield.
Slected Spectroscopic Data of products
8
The traditional phase transfer catalysts, such as TMAC and 18-crown-6,
have good catalytic activity. However, these are difficult to separate from the
reaction media for recycling because of their strong solubility.9-10It is more
attractive if such reactions can be performed using reusable catalysts. Triphase
catalysts(TCs) prepared by employing soluble phase transfer catalysts grafted
on polystyrene, which not only inherit their soluble analogs’ activity but also
are easily recycled and reused. At present, TCs have been applied very well in
many unit reactions, such as hydroxylation, 11 halogenating, 12 oxidation13 and
alkylation14, etc. However, to the best of our knowledge, application in ester
condensation has not previously been reported. As part of a continuous effort
to develop green esterification technology, a series of macroporous polystyrene
grafted quarternary ammonium salts had been prepared and applied as TCs in
synthesis of unsaturated esters in our work.
Compound a: IR(KBr, cm-1): 3083, 2945, 2882, 1730, 1649, 1600, 1579,
1500, 1448, 1276. 1H-NMR: δ 4.79(d, J=6Hz, 4H, -CH2O-), 5.27~5.48(m, 4H,
=CH2), 5.84~6.06(m, 2H, =CH-), 7.54(d, J=8Hz 2H, ArH), 7.79(d, J=8Hz ,2H,
ArH). 13C-NMR: 165.8, 133.5, 132.5, 128.2, 118.3, 67.2
Compound b: IR(KBr, cm-1): 3081, 3050, 2951, 2850, 1724, 1650, 1603,
1585, 1450, 1271, 1110. 1H-NMR: δ 4.76(d, J=6Hz, 2H, -CH2-), 5.25~5.62(m,
2H, =CH2), 5.75~6.03(m, 1H, -CH=), 7.38(m, 3H, Ar-H), 8.03(m, 2H, Ar-H).
13C-NMR: 165.9, 133.5, 132.1, 130.0, 129.8, 128.5, 67.1
Compound c: IR(KBr, cm-1): 3100, 3050, 2950, 2900, 1725, 1650, 1615,
1581, 1460, 1380, 1270, 1100. 1H-NMR: δ 2.35(s, 3H, -CH3), 4.86(d, J=6Hz,
2H, -CH2-), 5.35~5.62(m, 2H, =CH2), 7.21(d, J=8Hz, 2H, Ar-H), 6.11~6.45(m,
1H, -CH=), 8.08(d, J=8Hz, 2H, Ar-H). 13C-NMR: 165.8, 142.7, 132.5, 129.8,
128.6, 127.0, 67.0, 21.4
Compound d: IR(KBr, cm-1): 3131, 3070, 2950, 1725, 1680, 1612, 1530,
1
Scheme 1. Synthesis route of unsaturated esters
1354, 1455, 1278, 1105. H-NMR: δ 4.93(d, 2H, -CH2-), 5.42~5.73(m, 2H,
=CH2), 6.10~6.38(m, 1H, -CH=), 8.36(br, 4H, Ar-H). 13C-NMR: 165.9, 152.3,
136.2, 132.3, 130.6, 124.1, 67.0
EXPERIMENTAL
Compound e: IR(KBr, cm-1): 3075, 2938, 1736, 1587, 1363, 1310, 1103,
1021. 1H-NMR: δ 4.95(d, J=6Hz, 2H, -CH2-), 6.10~6.23(m, 1H, -CH=),
5.33~5.57(m, 2H, =CH2), 7.65(d, J=9Hz 1H, Ar-H), 7.93(d, J=9Hz, 1H, Ar-H),
8.35~8.90(m, 2H, Py-H). 13C-NMR: 165.8, 149.2, 140.5, 132.1, 128.3, 127.2,
126.6, 118.2, 67.0
Reagents and Apparatus
Chloromethylated polystyrene (PS-CH Cl) which content of chlorine is
12.8%, is obtained from Hebi Resin Factory2( Henan, China). The particle size,
specific surface and pore volume of PS-CH2Cl are 20~50 mesh, 99.8 m3·g-1 and
0.92 cm3·g-1 respectively. All other chemicals (AR grade) were commercially
available and used without further purification.
Infrared spectra were recorded with Bomen MB154S FT-IR spectrometer.
1H-NMR and 13C-NMR spectra was recorded on a Bruker AVII-400 MHz
spectrometer with TMSas the internal standard in DMSO-d6. The chromaticity,
Compound f: IR(KBr, cm-1): 3090, 2989, 2934, 2861, 1745, 1175.
1H-NMR: δ 2.09(s, 3H, -CH3), 4.61(d, J=8Hz, 2H, -CH2-), 4.91~5.05(m, 2H,
=CH2), 5.81(dd, 1H, -CH=). 13C-NMR: 170.5, 132.2, 118.2, 65.5, 20.8
Compound g: IR(KBr, cm-1): 3085, 2985, 2945, 2885, 1743, 1187.
1H-NMR: δ 1.20(t, J=7Hz 3H, -CH3), 2.31(q, J=7Hz 2H, -CH2-), 4.50(d, J=6Hz
e-mail address: lzy781103@zzu.edu.cn
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J. Chil. Chem. Soc., 58, Nº 1 (2013)
2H, -OCH -), 4.81~5.07(m, 2H, =CH2), 5.65(dd, 1H, -CH=). 13C-NMR: 173.8,
132.7, 1182.3, 65.7, 27.7, 9.5
Inhibition of Cu powder
Both allyl chloride and DAP have unsaturated bonds, which can generate
polymerization under condition of high temperature. Therefore, inhibitor
is often chosen to improve the product yield. In traditional process, phenols
are frequently used as an excellent inhibitor, but they are not convenient for
recovery, and possess the possibility of cancer. By contrast, Cu powder is an
effective and easy-recycled inhibitor. Its inhibition effect is demonstrated in
Table 3.
Compound h: IR(KBr, cm-1): 3092, 2960, 2923, 2872, 1759, 1645, 1420,
1382, 1276, 1190, 1090, 988. 1H-NMR: δ 4.05(s, 2H, -CH2Cl), 4.68(d, J=8Hz,
2H, -OCH2-), 5.25~5.47(m, 1H, -CH=),5.30~5.91(m, 2H, =CH2). 13C-NMR:
167.3, 132.5, 118.5, 65.3, 40.8
Compound i: IR(KBr, cm-1): 3088, 2979, 1745, 1345, 1250, 1256, 1185.
1H-NMR: δ 2.54(t, 4H, -CH2-), 4.45(d, J=6Hz, 4H, -OCH2-), 4.85~5.12(m, 4H,
=CH2), 5.69(m, 2H, -CH=). 13C-NMR: 175.0, 132.1, 118.7, 65.6, 29.9
Compound j: IR(KBr, cm-1): 3099, 2956, 1729, 1512, 1405, 1288,
TABLE 3. The effect of Cu amount on reaction phenomena and yield of
DAP.
1
1190, 1054, 811. H-NMR: δ 4.72(d, J=6Hz 2H,-CH2O-), 5.27~5.38(m, 2H,
=CH2), 6.15 (m,1H,=CH-), 5.95(q,1H, H-CH=CH-C=O), 6.03(dd,1H, =CH-
C=O),6.37(d, J=10Hz, 2H,H-CH=CH-C=O). 13C-NMR: 166.8, 132.4, 130.0,
128.9, 118.2, 65.1
Yield
/%
Run m(Cu)/g
phenomenon
Product color
RESULTS AND DISCUSSION
1
2
3
4
0
30
50
Obvious polymerization
Slight polymerization
No polymerization
72.5
84.2
91.7
92.3
Yellow
Pale yellow
Colorless
Colorless
Catalytic activity and reusable property of TCs
The catalytic properties of supported phase transfer catalysts are relevant
to many factors, such as the amount of grafted quaternary ammonium salts,
space structure and hydrophile-lipophile balance. The catalytic effect of TC-
1~6 in preparation of diallyl phthalate (DAP) is demonstrated in Table 1.
62.5
No polymerization
Note: n(sodium phthalate) = 0.1 mol, n(3-chloropropene) = 0.4 mol,
m(TC-1)=2.0g, m(NaI)=0.75g,V(H O) = 20 mL,, reflux for 4h
The product obtained from R2un 5 or 7 is almost colorless liquid after
vacuum distillation, whose important properties are demonstrated in Table 4.
TABLE 1. Immobilization amont of tertiary amine and catalytic capability
of different TCs.
TABLE 4. Specifications of competitive product of DAP.
TC
TC -1
TC -2
TC -3
TC -4
TC -5
TC -6
acid
value
iodine
value
/gI2.
Sepe-
cifica-
tion
chroma
(Co-
Pt)
Amount
immobilized
/mmol. g-1
w(DAP) density
/%
20
nD
/g.cm-1
/mg
2.11
91.7
3.90
64.2
2.53
81.6
2.83
78.7
1.12
81.0
1.43
88.5
KOH.g-1
100g-1
Yield/%
180~
200
99.5
1.15
1.517
0.049
35~50
Note: n(sodium phthalate) = 0.1 mol, n(3-chloropropene) = 0.4 mol,
m(TC) = 2.0g, m(NaI)=0.75g,V(H O) = 20 mL,m(Cu )=50mg, reflux for 4h
Essentially, reaction between2phthalic acid anion and allylhalide belongs
to S 1 nucleophilic substitution reaction. Phthalic acid anion is a soft base
accoNrding to stand of hard and soft acid and base. Based on the theory of Lewis
acid-base, soft base with its hardness matching soft acid has a strong affinity.
Above the six catalysts, the affinity of TC-1 with phthalic acid anion is the
strongest. Besides, TC-1 belongs to high polymer cationic surfactant, which
can effectively reduce the oil-water interfacial tension and promote the mass
transfer. Meanwhile, compared with the traditional surfactants, TC-1 seldom
causes interface emulsification, which is benefit for the subsequent separation.
It is worth noting that NaI exhibits excellent synergistic effect with TCs.
On the one hand, TCs can provide good conditions for the substrates contacted
each other; on the other hand, NaI reacts with allyl chloride to get allyl iodine
which is highly reactive. When TC-1 was used alone, the yield of DAP is
only 75.8%. While TC-1 was used in presence of NaI, the reaction proceeded
smoothly in 91.7% yield at the same conditions.
Reaction temperature and reaction time
Owing to the lack of efficient catalyst system, most of the former methods
to prepare DAP suffered from high temperature, high pressure or employment
of high boiling solvents. In our work, the catalyst system of TC-NaI is highly
active, whichcanremarkablelowerreaction temperatureandmakeesterification
smooth progress under reflux temperature at atmospheric pressure. Along
with the progress of reaction, allyl chloride was gradually being consumed
and reflux temperature is risen more and more, so the reflux temperature can
directly reflect the extent of reaction. Table 5 lists a corresponding relationship
of reflux time, reflux temperature and product yield.
TABLE 5 Corresponding relationship of reflux time, reflux temperature
and product yield.
Reflux time/h
Reflux temp/ºC
Yield/%
1
2
2.5
74
4
4.5
87
5
The most important advantage of the triphase catalysts is easy to recover
and reuse. After completion of the reaction, the catalyst was recovered by
simple filtration and reused directly in subsequent reaction with approximate
invariable activity. The reusage situation of TC-1 is shown in Table 2.
49
65
80
92
62.5 79.5 86.3 91.7 88.2 80.3
TABLE 2. The relationship between product yield and use times of TC-1.
Note: n(sodium phthalate) = 0.1 mol, n(3-chloropropene) = 0.4 mol,
m(TC-1) = 2.0g, m(NaI)=0.75g,V(H O) = 20 mL,m(Cu )=50mg
Table 5 indicates when reflux2temperature reached 80ºC, esterification
had closed to the end. Extending reaction time would further improve the
reflux temperature, which maybe allyl chloride was hydrolyzing to allyl
alcohol. When reflux temperature exceeded 85ºC, the color of reaction system
converted to palm red from light yellow along with black floccule and the yield
of DAP was gradually declined. It showed that effect of inhibitor decreased at
high temperature, polymerization reaction happened obviously.
Applicability of the process in preparation of various unsaturated
esters
Use times
Yield/%
1
2
3
4
5
6
91.7
89.6
88.2
89.1
85.7
83.9
Note℃n(sodium phthalate) = 0.1 mol, n(3-chloropropene) = 0.105 mol,
m(NaI)=0.75g,V(H2O) = 20 mL, m(Cu )=50mg, reflux for 4h
After using TC-1 six times, the yield of product decreased slightly, which
mainly attributed to catalyst mass loss. A small amount of catalyst was grinded
into powder by muddler during reaction. Unfortunately, the powdered catalyst
was suspended in filtrate after filtering. If supply a small amount of fresh TC-1
for next reactions, the yield could remain unchanged.
Finally, this protocol was extended to the synthesis of various unsaturated
esters via condensation of carboxylic acid Na and allyl chloride. The results
under optimum conditions are summarized in Table 6.
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J. Chil. Chem. Soc., 58, Nº 1 (2013)
TABLE 6. Synthesis of some important unsaturated esters.
Entry
RCOONa
Product
MR
T/h
Yield/%
COO
COONa
1
4
4
91.7
COO
COONa
a
COONa
COO
2
3
4
5
2
2
2
3
3
3
85.0
79.2
96.0
b
COONa
COO
c
H3C
H3C
O2N
COONa
COO
d
O2N
Cl
Cl
Cl
N
Cl
N
2
3
82.4
COO
COONa
e
6
7
2
2
2
2
91.5
89.8
CH3COONa
f
CH3COO
CH3CH2COONa
g
C2H5COO
8
ClCH2COONa
2
2
94.1
h
ClCH2COO
C3H5OOC
COOC3H5
COONa
i
9
4
2
3
3
81.6
78.2
NaOOC
COO
COONa
10
j
Note: n(RCOONa)=0.1mol, m(TC-1) = 2.0g, m(NaI)=0.75g,V(H2O) = 20 mL,m(Cu )=50mg, reflux for some time; MR=Molar ratio
1560

J. Chil. Chem. Soc., 58, Nº 1 (2013)
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In summary, we have developed a green, convenient and efficient
protocol for the synthesis of unsaturated esters in water catalyzed by TC-NaI
at atmospheric pressure. This method avoids the use of high pressure and
environmentally unfavorable volatile organic solvents. The most attractive
part of this work is that TCs are heterogeneous catalysts, and can be separated
conveniently from the reaction media after the reaction, and can be directly
reused for next time with no obvious activity declining.
ACKNOWLEDGMENTS
The authors thank the Natural Science Foundation of Henan Province,
China (project no. 2011B150036) for the support of this work.
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