Catalytic Activity of Quaternary Ammonium Poly(methylstyrene-co-styrene) Resin in an Organic Solvent/Alkaline Solution

Article abstract of DOI:10.1006/jcat.2001.3162

The reaction of 4-methoxyphenylacetic acid with n-bromobutane using triphase catalysis in a dichloromethane/alkaline solution was investigated. Meanwhile, the lab-produced resins and the commercial ion-exchange resin (triphase catalyst) were characterized in terms of the density of active sites, thermal stability, imbibed solvent composition, and reuse of the resin. The amount of active sites in the resin was characterized by EA, TGA, and Volhard methods. The imbibed amounts of organic solvent and water and the volume ratios for lab-produced resins were larger than those for commercial resins. The degradation of the catalyst due to temperature is greater than that due to base concentration.

Full text of DOI:10.1006/jcat.2001.3162

Journal of Catalysis 199, 217–223 (2001)
doi:10.1006/jcat.2001.3162, available online at http://www.idealibrary.com on
Catalytic Activity of Quaternary Ammonium
Poly(methylstyrene-co-styrene) Resin in an
Organic Solvent/Alkaline Solution
Ho-Shing Wu1 and Chun-Shen Lee
Department of Chemical Engineering, Yuan-Ze University, 135, Yuan-Tung Road, ChungLi, Taoyuan, 32026, Taiwan, Republic of China
Received August 7, 2000; revised January 4, 2001; accepted January 4, 2001; published online March 27, 2001
in the microenvironment must be determined in order to
obtain a high reactivity of triphase catalyst.
The reaction of 4-methoxyphenylacetic acid with n-bromobutane
using triphase catalysis in a dichloromethane/alkaline solution was
investigated. Meanwhile, the lab-produced resins and the commer-
cial ion-exchange resin (triphase catalyst) were characterized in
terms of the density of active sites, thermal stability, imbibed sol-
vent composition, and reuse of the resin. The amount of active sites
in the resin was characterized by EA, TGA, and Volhard methods.
The imbibed amounts of organic solvent and water and the volume
ratios for lab-produced resins were larger than those for commer-
cial resins. The degradation of the catalyst due to temperature is
c
Poly(styrene-co-chloromethylstyrene) crosslinked with
divinylbenzene, which is immobilized with quaternary am-
monium salts, was investigated to synthesize the fine
chemicals in our previous works (26–30). The microenvi-
ronment of the polymer support played a crucial role in
enhancing the reaction rate. More information about the
characterization of the polymer structure, the interactions
among organic solvent, resin, and aqueous solution, and
the reuse of the catalyst is required to encourage applica-
tion. Hence, in this study we aim to understand the mi-
croenvironment of the polymer support using instrumental
analysis with TGA, EA, and reaction methods. The syn-
thesis of 4-methoxybenzoic butyl ester (29) is shown in
Eq. [1].
greater than that due to base concentration.
2001 Academic Press
Key Words: phase-transfer catalysis; triphase catalysis; catalytic
activity; characterization; reuse.
INTRODUCTION
Quaternary onium salts, crown ethers, cryptands, and
polyethylene glycol have all been immobilized on var-
ious kinds of supports, including polymers (most com-
monly (methylstyrene-co-styrene) resin crosslinked with
divinylbenzene), alumina, silica gel, clays, and zeolites
(1–25). Because of diffusional limitations and high cost, the
industrial applications of immobilized catalysis (triphase
catalysis) are not fully utilized. This unfortunate lack of
technology for industrial scale-up of triphase catalysis is
mainly due to a lack of understanding of the complex in-
teractions between the three phases involved in such a sys-
tem. To date, there has been little literature discussion of
the microenvironment. The effect of the internal molecular
structure of the polymer support, which plays an impor-
tant role in the imbibed composition, on the reaction rate
has seldom been discussed. In addition to the reactivity, a
triphase catalyst in an organic and aqueous solution must be
selected with consideration of the volume swelling, imbibed
different solvent ratio, amount of active site, and mechani-
cal structure of catalyst. Hence, these complex interactions
[1]
Twelve kinds of lab-produced quaternary ammonium resins
and six kinds of commercial ion-exchange ammonium
resins were investigated, as described in the following.
EXPERIMENTAL
Preparation of Triphase Catalyst
The procedure for the synthesis of polymer-supported
phase-transfer catalyst (triphase catalyst) was identical to
that in our previous works (27, 30). The procedure for the
synthesis of the microporous resin was identical to that for
macroporous resin, except that 4-methyl-2-pentanol was
used as the pore-creating agent. The typical compositions
of styrene, chloromethylstyrene, and divinylbenzene
(crosslinking) in the resin were 76 wt% , 20 wt% , and
4 wt% , respectively. The particle sizes of the polymer pellet
were determined by sieve analysis. Weight percents of
microporous polymer collected were 20–40 mesh = 16% ,
40–80 mesh = 31% , 80–120 mesh = 27% , 120–200 mesh =
19% , and 200–400 mesh = 7% .
1
To whom correspondence should be addressed. E-mail: cehswu@
ce.yzu.edu.tw. Fax: (+886)-3-455-9373.
217
0021-9517/01 $35.00
c
Copyright
2001 by Academic Press
All rights of reproduction in any form reserved.

218
WU AND LEE
A 20.0 g amount of polymer pellets, 40 cm3 of dimethyl- then removed from the slurry using an aspirator. The wet
formamide, and 60.0 g of tri-n-butylamine were intro- resin was placed in a flask containing 15 cm3 of dimethylfor-
duced into a 250-cm3 flask at 60 C. The reaction mixture mamide from the catalyst pellets. The amounts of solvent
was agitated (400 rpm) for 6 days. The polymer was then and water in dimethylformamide were measured by HPLC
filtered and washed with methanol, acetone, and anhydrous and potential meter (Karl Fischer titration), respectively.
P
vol. of wet swollen resin
methanol, and dried under vacuum at 60 C.
Volume ratios (VR =
=
i (msi /
+
si
mp/ p)/mp/ p) were calculvaotle. odf bdryy aresssinuming that the poly-
mer density pwas 1060 kg/m3 (vs 1040–1065 kg/m3 for
amorphous polystyrene) and the densities of the solvents
si and polymer in the resin were the same as those of pure
solvent and pure polymer. mp and msi denote the masses
of polymer and solvent, respectively, in the resin. Direct
measurement of the porosity of the wet swollen resin was
very difficult because of the solvent within the pores. The
porosity of the wet swollen resin was thus estimated as
ε = 1 1/VR.
The lab-produced resins were determined to be mi2-20,
mi4-20, and ma2-20, etc. The notations “mi” and “ma”
indicate microporous and macroporous, respectively. The
first number is the percentage of crosslinking for divinyl-
benzene in the resin and the second is the percentage
of ring substitution for chloromethylstyrene in the resin.
The molecular structure of polymer-supported (styrene–
chloromethylstyrene– divinylbenzene) resin is expressed as
Kinetics of the Triphase Catalytic Reaction
For a kinetic run, an aliquot sample was withdrawn
from the reaction solution at a selected time interval. The
sample (0.2 cm3) was immediately added to the solution
(0.5 cm3 dichloromethane/0.5 cm3 of diluted hydrochloric
acid) to quench the reaction. The organic phase content
was then quantitatively analyzed by HPLC using the inter-
nal standard method.
Characterization of Resins
The procedure for determining the imbibed solvent com-
position of the resin is identical to that in Wang and Wu’s
1992 report (28). A 125-cm3 funnel equipped with a frit-
ted disk served as the testing apparatus. Known quantities
of the catalyst pellet, organic solvent, and alkaline solution
were added to the funnel. The external liquid phase was
RESULTS AND DISCUSSION
The content of tri-n-butylamine immobilized in the resin
was determined by the TGA, EA, and Volhard methods.
The solid and dashed lines, as shown in Fig. 1a, indicate the
FIG. 1. Thermogravimetric curve of weight loss versus operating temperature for various resins.

ACTIVITY OF POLY(METHYLSTYRENE-co-STYRENE) RESIN
219
TABLE 1
thermal analysis of the resin mi4-20 of the polymer back-
bone and the polymer backbone with the functional group
–N(C4H9)3, respectively. The polymer backbone formed in
a one-stage process where the decomposing temperature
range was 300 to 450 C. The immobilized resin (mi4-20) was
formed in a two-stage process, where the ranges of decom-
position temperatures for the two stages were 160 to 200 C
and 350 to 450 C. Although it is tempting to divide the two
stages into two distinct units, the correlation between qua-
ternary salt content and weight loss in the first step (weight
at point m- weight at point n, as shown in Fig. 1a) was quali-
tative. The weight loss in the first step is equal to the amount
of the immobilized functional group –N(C4H9)3. The an-
alytical technique was accurate to within 10% . The char
yield at 600 C for TGA analysis of lab-produced resins
was around 7% , which indicates the total amount of the
metal salt in the resin. Figure 1b shows the TGA analysis of
the commercial ion-exchange resin. These resins were re-
vealed in a three-stage process. The decomposed compound
and temperature for each decomposition step are imbibed
water, 100 C; functional group, 160–300 C; and polymer
backbone, 350–450 C. The sequence of the imbibed capa-
bility of water was IRA-900 (20% ) > A-26 > Dowex 1
2 > A-27 IRA-410 > IRA-904 > mi4-20 (4% ). Most com-
mercial ion-exchange resins have a hydrophilic functional
group. The decomposition temperatures of the functional
groups of A26, IRA-410, and Dowex 1 2 (220–350 C) are
larger than those of IRA-900, IRA-904, A27, and mi4-20
(160–220 C). The sequence of the char yield at 600 C for
TGA analysis is IRA-904 (21% ) > A-27 IRA-900 > A-
26 > Dowex 1 2 > IRA-410 > mi4-20 (7% ). This finding
demonstrates that the salts in the resin synthesis process
still remain in the resin. The resident salt will influence the
utility of the resin in a triphase reaction, e.g., the imbibed
solvent composition in the resin.
In addition, the amount of functional group –N(C4H9)3
immobilized in the resin wasdetermined from the massfrac-
tion of nitrogen by elemental analysis (EA) for C, H, and
N, from the weight loss at 160 to 200 C by TGA, and from
the chloride ion density titrated by the Volhard method.
Table 1 lists the content of tri-n-butylamine immobilized in
the resin as determined by EA, TGA, and Volhard meth-
ods. The accuracy levels of our analytical techniques for
TGA, EA, and Volhard methods were within 10% , 5% ,
and 3% , respectively. The sequence of the methods for the
determination of the content of tri-n-butylamine immobi-
lized in the resin was TGA > EA > Volhard, as shown in
Table 1. The TGA (or EA) analysis was based on the ele-
mental weight, and it reveals the real immobilized content.
However, the Volhard method determined the amount of
free chloride ion in the solution by the AgNO3 titration
method. The content of tri-n-butylamine immobilized in
the resin as determined by the TGA (or EA) method was
20% larger than that determined by the Volhard method.
Amount of Functional Group (–N(C4H9)3Cl) in the Resin
Micro resin (mmol/g)
Macro resin (mmol/g)
Resin
TGA
EA
Volhard
TGA
EA
Volhard
2-20
4-20
6-20
4-30
4-40
4-60
1.026
1.072
1.026
1.305
1.632
2.331
0.986
0.936
1.286
1.171
1.564
2.036
0.743
0.716
0.530
0.943
1.036
1.452
1.399
1.632
1.678
1.505
1.585
2.051
1.593
1.457
1.929
1.501
1.671
1.90
0.994
0.844
0.964
0.901
1.36
1.506
Note. The theoretical amount of functional group (–N(C4H9)3Cl) in
the resin of mi4-20 is 1.7 mmol/g.
The content of tri-n-butylamine immobilized in the resin
as determined by the TGA (or EA) method was indepen-
dent of the number of crosslinks, and only dependent of the
number of the ring substitutions. The experimental results
in Table 1 demonstrate the following:
(i) The percentage of the active site in the resins (number
of ring substitutions) was smaller than that for addition of
chloromethylstyrene to the polymer backbone for the syn-
thesis (theoretical value). The theoretical ratio (60/20 =
3) of mi4-60 to mi4-20 was not equal to the immobilized
content (2.331/1.072 = 2.33 for TGA) of mi4-60 to mi4-20.
(ii) In this study, tri-n-butylamine could be immobilized
completely with the active site on the resin for an immo-
bilized duration of 6 days. However, the content of im-
mobilized tri-n-butylamine as determined by the Volhard
method was dependent on both the number of crosslinks
and the number of ring substitutions. The immobilized con-
tents for the Volhard method are about 50–70% of that for
TGA (or EA). Since the results of the Volhard analysis
method determined the free chloride ions in the solution
by the AgNO3 titration method, the free chloride ions on
the active site were measured at only 50–70% of the amount
of immobilized content. The trend in the varied content for
microresin is larger than that for macroresin. This result
indicates that analysis by the Volhard method may be in-
fluenced by the diffusion problem. The results may be due
to the fact that the resin had not swelled completely in the
aqueous solution. On the other hand, if the resin is used
as triphase catalyst to react in an actual reaction system,
and the resin could not swell completely to release all free
chloride ions, then the reaction environment would be in-
fluenced by the mass transfer of the reactant.
Figure 2 shows the amount of imbibed solvent, vol-
ume ratio, and porosity of 12 kinds of ion-exchange resins
for seven kinds of solvents (dichloromethane, chloroform,
1,2-dichloroethane, benzene, toluene, chlorobenzene, and
water) when 1 g of the resin was placed into 25 cm3 of
the pure solvent. The experimental results for the com-
mercial ion-exchange resin are as follows. (i) The amounts

220
WU AND LEE
FIG. 2. Effect of solvent on the imbibed weight of solvent, volume ratio, and porosity for various resins in the chlorobenzene/water system:
solvent = 25 cm3, resin (45–60 mesh) = 1 g, 25 C.
of the imbibed solvent for the aromatic solvents (ben- and chlorobenzene, and increased for the solvents chlo-
zene, toluene, chlorobenzene) were larger than those for roform, 1,2-dichloroethane, dichloromethane, and water,
halide aliphatic solvents (dichloromethane, chloroform, with increasing number of ring substitution. These results
1,2-dichloroethane) since the resin was made from styrene. indicate that the solubility of water in chloroform, 1,2-
The sequence of the imbibed amount for the aromatic sol- dichloroethane, and dichloromethane is larger than the sol-
vents is benzene > toluene > chlorobenzene. (ii) The im- ubility in benzene, toluene, and chlorobenzene. The im-
bibed amounts for water and organic solvent were around bibed amount for aromatic solvents was larger than that
1 g and less than 1 g, respectively. (iii) The volume ratios for halide aliphatic solvents when the number of ring sub-
were between 1 and 2. (iv) The porosities were between 0.5 stitutions was small, and the trend was opposite when the
and 0. The porosity of the ion-exchange resin was about 0.5 number of ring substitutions was large.
(31).
Because the functional group (tetra-n-butylammonium
The experimental results for the lab-produced resins are chloride) of the lab-produced resin is more lipophilic
as follows. (i) The amounts of the imbibed solvent were than that (tetramethyl(or ethyl)ammonium chloride) of the
dependent on the structure of the resins. The amount of commercial ion-exchange resin, the amount of imbibed
imbibed solvent for water was smaller than that for or- water was larger than that of the organic solvent for the
ganic solvent. (ii) The amounts of imbibed solvent were commercial resin, and in contrast, for the lab-produced
in the range of 0 to 3. (iii) The volume ratios were al- resin, the amount of water was less than that of organic
most all between 1 and 3. The volume ratio decreased solvent. The imbibed amount of organic solvent for the
with increasing crosslinking of the resin. (iv) The porosi- lab-produced resin was larger than that for the commer-
ties were between 0.25 and 0.75. The porosity and im- cial resin, as shown from the ε values in Fig. 2. Although
bibed amount decreased for the solvents benzene, toluene, the swollen volumes of A-27 and IRA-904 were high in the

ACTIVITY OF POLY(METHYLSTYRENE-co-STYRENE) RESIN
221
FIG. 3. Plot of apparent reaction rate constant for various resins: 1000 rpm, resin = 1.5 g, KOH (7 kmol/m3) = 50 cm3,CH3OC6H4CH2COOH =
0.03 mol, 1-Br(C4H9) = 0.073 mol, 55 C.
commercial resin, the others were not good for swelling.
Figure 3 shows the effects of the degree of crosslink-
Hence, the commercial resins are not suitable for use as ing, the number of ring substitutions, and various kinds
phase-transfer catalyst in an organic phase/aqueous solu- of resins on the reactivity of the 4-methoxybenzoic butyl
tion reaction system.
ester reacting with 4-methoxyphenylacetic acid and n-
bromobutane using triphase catalysis. Increasing the de-
gree of crosslinking for both the micro resin and the macro
resin decreased the apparent reaction rate constant, and
the reactivity for the macro resin was larger than that for
the micro resin (Fig. 3a). The apparent reaction rate con-
stant remained constant for the micro resin and had a
minimum value for the macro-resin with increasing num-
ber of ring substitutions, and the reactivity for the macro
resin was smaller than that for the micro resin (Fig. 3b).
The reactivity for six commercial ion-exchange resins was
very low (Fig. 3c). According to the results in Fig. 2,
the functional group of the commercial resins was a hy-
drophilic group (tetramethyl(or ethyl)ammonium); in fact,
the imbibed solvent ratio of organic solvent to water was
small. The imbibed solvent ratio and hydrophobicity of the
resin were increased with increasing carbon number in the
alkyl group. Figure 3c shows the reactivity for two resins
(4-20-O and 4-60-O) for which the functional group is the
tetra-n-octylammonium group. The reactivity for tetra-n-
[2] octylammonium was also smaller than that for the tetra-
butylammonium group. Hence, the excessive hydrophilic-
Reaction of 4-Methoxyphenylacetic Acid
with n-Bromobutane
The rate of the triphase reaction is controlled by many
factors, including the reactivity of the active site, degree
of crosslinking, degree of swelling, number of ring sub-
stitutions, particle size, temperature, and imbibed solvent
composition in the resin. Hence, the reaction of 4- methoxy-
benzoic butyl ester with 4-methoxyphenylacetic acid and
n-bromobutane using triphase catalysis investigated by
our previous work (29) was chosen as a model reaction
to understand the relationship between the reaction phe-
nomenon and the structure of the resin. The reaction rate
for the organic phase follows pseudo-first-order kinetics
and can be written as
r
= r
BrC4H9
CH3OC6H5COOC4H9
= kBrC H [resin+CH3OC6H4COO ][BrC4H9]
4
9
= kf,app[BrC4H9],
where kf,app is the apparent reaction rate constant for for- ity or lipophilicity of the functional group is not of use in
mation of 4-methoxybenzoic butyl ester. The effects of tem- the triphase catalytic reaction.
perature, base, structure,and reuse of the resin are discussed
in the following.
In general, the reaction rate increases with augmen-
tation of the polarity of the solvent. In this study, five

222
WU AND LEE
TABLE 2
Activation Energies for the Reaction of 4-Methoxyphenylacetic
Acid with n-Bromobutane in Various Solvents
Ea (kcal/mol)
C6H5Cl
C6H6
C6H5CH3
CH2Cl2
CHCl3
Micro resin
Macro resin
15.8
14.1
17.1
14.3
19.9
14.6
15.8
13.0
12.1
13.0
Conditions. 1000 rpm, resin = 1.5 g, KOH (7 kmol/m3) = 50 cm3,
CH3OC6H4CH2COOH = 0.03 mol, 1-Br(C4H9) = 0.073 mol.
kinds of solvents with various polarities were used as
the organic solvents in the triphase catalytic reaction.
The sequence of the reactivity for the macro resin was
CH2Cl2 > CHCl3 > C6H5Cl > C6H6 > C6H5CH3, and the
trend for the micro resin was similar, except for chloroform.
The increment of the reactivity of this triphase reaction
corresponds to the polarity of solvent. Dichloromethane
had the highest reactivity among the solvents. However,
the boiling point of dichloromethane is 39 C, and it is im-
practical for reaction in the higher temperature reaction
system. Table 2 lists the Arrhenius activity energy for vari-
ous solvents. The activity energy varied with the structure of
the resin. Most activity energy levels for micro resins were
larger than those for macro resins, except for chloroform.
The four functions of a base in a liquid–solid–liquid
triphase catalytic reaction were reported in our previous
work (Wu and Meng, 1999) (30): (i) as a reactant; (ii) in
deprotonation of the acidic organic compound to become
the reactive form; (iii) for improving the reactive environ-
ment in the catalytic pellets, such as swelling volume, im-
bibed composition, solubility between two phases, etc.; and
(iv) for reducing the solvation of catalyst and water to up-
grade the reactivity of active catalyst in the organic phase.
Figure 4 shows the effect of base concentration for the re-
activity of 4-methoxyphenylacetic acid. The apparent re-
action rate constant was almost constant when the NaOH
(or KOH) concentration was larger than 1 kmol/m3. The
increment of the deprotonation of 4-methoxyphenylacetic
acid dramatically increased the reactivity of the reaction
when the base concentration was below 1 kmol/m3. When
the salt concentration was increased to change the reaction
environment, the reactivity of the reaction was slightly in-
creased with increasing base concentration. The reactivity
for KOH was larger than that for NaOH.
FIG. 4. Effect of base concentration on apparent reaction rate con-
stant for various resins: 1000 rpm, resin = 1.5 g, base solution = 50 cm3,
CH3OC6H4CH2COOH = 0.03 mol, 1-Br(C4H9) = 0.073 mol, 55 C.
The advantages of using triphase catalytic reaction are
that it easily recovers the catalyst and purifies the prod-
uct and reactant. Hence, the reuse, stability, and degra-
dation of the catalyst must always be considered. Resins
with onium groups may be used for extended periods or
repeated cycles only if the catalyzed reactions occur un-
der sufficiently mild conditions to avoid degradation. The
FIG. 5. Effect of base concentration on the amount of active site in
the resin determined by elemental analysis after 5 h for the formation of
4-methoxyphenoxyacetic acid butyl ester: 1000 rpm, resin (45–60 mesh) =
1.5 g, base solution = 50 cm3, CH3OC6H4CH2COOH = 0.03 mol, 1-
Br(C4H9) = 0.073 mol, 55 C. (a) Microporous resin; (b) macroporous
resin.

ACTIVITY OF POLY(METHYLSTYRENE-co-STYRENE) RESIN
223
degradation of the catalyst dramatically increased when the
temperature was higher than 60 C.
ACKNOWLEDGMENTS
We thank the National Science Council of Taiwan, Republic of China,
for financial support of this research under Contract No. NSC 85-2214-
E155-002.
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FIG. 6. Effect of temperature on the amount of active site in the
resin determined by elemental analysis after 5 h for the formation of
4-methoxyphenoxyaceticacid butylester:1000rpm, resin (45–60mesh) =
1.5 g, KOH (7 kmol/m3) = 50 cm3, CH3OC6H4CH2COOH = 0.03 mol,
1-Br(C4H9) = 0.073 mol.
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degradation of the triphase catalyst may be due to three fac-
tors: high temperature, strong base, and mechanical degra-
dation. In the past literature (14, 15, 32–35), the reac-
tivity of the triphase reaction was influenced slightly by
the degradation of the catalyst (polymer-supported resin).
From Figs. 5 and 6, the active site is seen to decrease
slightly with increasing base concentration up to 9 kmol/m3
(Fig. 5). The number of active sites remained constant up
to 60 C, and then decreased dramatically as the temper-
ature increased (Fig. 6). The degradation of the catalyst
with temperature is more extreme than that with base
concentration.
CONCLUSIONS
25. Naik, S. D., and Doraiswamy, L. K., AIChE J. 612 (1999).
26. Wang, M. L., and Wu, H. S., Ind. Eng. Chem. Res. 31(2), 490 (1992).
27. Wang, M. L., and Wu, H. S., J. Polym. Sci.: Polym. Chem. 30(7), 1393
(1992).
The amount of active sites in the resin was characterized
by EA, TGA, and Volhard methods. The accuracy of ana-
lyzing active sites by EA was the best of the three methods, 28. Wang, M. L., and Wu, H. S., Ind. Eng. Chem. Res. 31(9), 2238
(1992).
followed by the TGA method. In addition, the TGA data
can indicate the amount of the functional group type and
the resident metal salt in the resin. The amount of active
sites determined by using the Volhard method was low be-
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