Selective O-allylation of bisphenol A: Toward a chloride-free route for epoxy resins

Article abstract of DOI:10.1002/aoc.1743

The O-allylation of bisphenol A (BPA) has been performed with the most selective catalysts for O-allylation of phenols reported previously. Both the cyclopentadienyl-ruthenium catalysts and the palladium-diphosphine catalysts are capable of selectively performing single and double O-allylation of BPA. An intriguing solvent effect is observed; the choice of the solvent is of key importance for both conversion and selectivity. The use of an excess of diallyl ether as allylating agent results in relatively high yields of the bisallyl ether of bisphenol A, while maintaining the high selectivity for O-allylation.

Full text of DOI:10.1002/aoc.1743

Full Paper
Received: 3 August 2010
Revised: 17 September 2010
Accepted: 13 October 2010
Published online in Wiley Online Library: 8 December 2010
(wileyonlinelibrary.com) DOI 10.1002/aoc.1743
Selective O-allylation of bisphenol A: toward
a chloride-free route for epoxy resins
∗
Jimmy A. van Rijn, Marieke C. Guijt, Elisabeth Bouwman , and Eite Drent
The O-allylation of bisphenol A (BPA) has been performed with the most selective catalysts for O-allylation of phenols reported
previously. Both the cyclopentadienyl–ruthenium catalysts and the palladium–diphosphine catalysts are capable of selectively
performing single and double O-allylation of BPA. An intriguing solvent effect is observed; the choice of the solvent is of key
importance for both conversion and selectivity. The use of an excess of diallyl ether as allylating agent results in relatively high
yields of the bisallyl ether of bisphenol A, while maintaining the high selectivity for O-allylation. Copyright ꢀc 2010 John Wiley
&
Sons, Ltd.
Keywords: allylation; bisphenol A; allyl alcohol; diallyl ether; catalysis
[
14]
Introduction
below. The structures of the catalysts [RuCp(dppb)](OTs),
RuCp(PPh3)2](OTs),[
16]
the immobilized complex [RuCp(PPh3)
resinPhPPh2](OTs) and Pd(OAc)2 with the diphosphine ligand
[
(
In the context of the development of an environmentally benign
catalytic route to epoxy resins, a two-step route is proposed
consisting of the O-allylation of bisphenol A, followed by the
oxidation of the two olefinic groups to obtain the bisglycidyl
[18]
[17]
dppdmp are shown in Fig. 1.
[
1]
ether of BPA (Scheme 1). Several studies of the allylation of BPA
have been reported, but these studies do not make use of allyl
alcohol (or its condensed derivative diallyl ether); instead allyl
Experimental
General Remarks
halides,[
2–8]
allyl acetate
[1,9]
or allyl carbonate
[10–13]
are employed
All reactions were performed under an argon atmosphere using
standard Schlenk techniques. Solvents were dried and distilled by
standard procedures and stored under argon. Bisphenol A was
obtained as a gift from Hexion Speciality Chemicals and was used
as received. Procedures for the synthesis of the catalysts have been
reported previously by us.[
as the allylating agent. A stoichiometric amount of base is often
necessarytocreatethephenolateanionsin situ,thusincreasingthe
nucleophilicity of the O-position. Allyl alcohol, however, would be
amuchmoreattractiveallyldonor, sinceonlywaterisco-produced
in allylation reactions. Thus allyl alcohol can be considered as a
14,16–18]
‘
green’ reagent, but only if no other reagents are necessary in
stoichiometric amounts to control activity and selectivity.
In our previous work detailed studies of O-allylation of phenols
Catalytic Procedures
have been reported.[
14–18]
4-Tert-butylphenol was mainly used as
Reactions with Ru catalysts
a model substrate for bisphenol A, in order to simplify the analysis
of the multiple products that can be formed. Our investigation has
led to a better understanding of the mechanism for O-allylation of
phenols with allyl alcohol and revealed the specific requirements
foragoodcatalystandoptimalreactionconditions.Theconversion
of the phenol into the allyl phenyl ether turned out to be limited
due to the presence of an equilibrium reaction. Not only allyl
alcohol but also diallyl ether, the condensation product of two
molecules of allyl alcohol, turned out to be a suitable allylating
agent. Having established the requirements for the selective O-
allylation of a phenol with allyl alcohol to form an allyl phenyl
ether, BPA has now been used as the ultimate substrate.
The goal of the research thus was to perform a double
O-allylation as shown in Scheme 1, without the need for
stoichiometric additives. Whereas in the allylation of 4-tert-
butylphenol a total of four products was observed, in the allylation
ofBPAatotalof14differentproductscantheoreticallybeobtained,
underlining theimportanceofthedevelopmentofhighlyselective
catalysts. Several catalytic systems that were found to yield the
bestresultsfortheselectiveO-allylationofphenolshavenowbeen
used in the catalytic allylation of BPA and the results are described
A 1.25 mmol aliquot of BPA, 2.5 µmol of Ru complex, 5.0 µmol of
AgOTs and 0.05 mmol HOTs (p-toluenesulfonic acid) were charged
into the reaction vessel and flushed with argon. Degassed and
dried toluene or n-heptane (2.5 ml, unless stated otherwise) was
added and the mixture was stirred for 5 min. The allyl donor
was added and the reaction mixture was heated to reaction
temperature. Samples were taken at certain time intervals and
analyzed by HPLC.
Reactions with Pd catalyst
A 1.25 mmol aliquot of BPA, 2.5 µmol of Pd(OAc)2 and 10 µmol
of dppdmp were charged into the reaction vessel and flushed
∗
Correspondenceto:Elisabeth Bouwman,LeidenInstituteofChemistry,Gorlaeus
Laboratories, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands.
E-mail: bouwman@chem.leidenuniv.nl
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, PO Box
9502, 2300 RA Leiden, The Netherlands
Appl. Organometal. Chem. 2011, 25, 207–211
Copyright ꢀc 2010 John Wiley & Sons, Ltd.

J. A. van Rijn et al.
2
H O
2
OH
[cat]
HO
OH
+
O
O
2ROOH
[cat]
2ROH
O
O
O
O
Scheme 1. Proposed chlorine-free and salt-free process towards bisglycidyl ether of bisphenol A.
(a)
(b)
(c)
(d)
+
+
+
-
OTs
-OTs
-OTs
Pd(OAc)2
+
Ru
Ru
Ru
Ph P
PPh2
2
Ph P
PPh2
Ph3P
PPh3
Ph2P
PPh3
2
Figure 1. Structure of the catalyst used in the allylation of bisphenol A: (a) [RuCp(dppb)](OTs); (b) [RuCp(PPh3)2](OTs); (c) [RuCp(PPh3) (resinPhPPh2](OTs);
d) Pd(OAc)2 + dppdmp.
(
with argon. Degassed and dried toluene (2.5 ml unless stated
otherwise) was added and the mixture was stirred for 5 min. The
allyl donor was added and the reaction mixture was heated to
reaction temperature. Samples were taken at certain time intervals
and analyzed by HPLC.
can theoretically be obtained, each with high molecular weight
precluding the use of GC as an analytical tool. It was found that
products 3–7 are efficiently separated by means of HPLC and
characterized with LC/MS. The O-allylated products 3 and 4 were
also synthesized by reported procedures,[ characterized by NMR
spectroscopy and LC/MS. The response factors in UV detection
proved to be independent of the allylic substitution. The BPA is
initially mono-allylated, yielding either the O- (3) or C-allylated
(5) product, before one of the rings is substituted with a second
allyl moiety, which only occurs after longer reaction times. This
product development is observed in all the allylation reactions
of BPA. The tris-allylated products are only present in very low
concentrations for the less selective reactions; these products
could not be separated efficiently. The selectivity for O-allylation
discussed below is defined by calculating the percentage of O-
allylated products (3 + 4; Scheme 2) on the total amounts of
products formed.
5]
Procedure of Dow patent reaction
A mixture of 285 mg (1.25 mmol) BPA, 36 mg [RuCpCl(PPh3)2]
(
2 mol%) and 2.5 g (25 mmol) allyl acetate under an argon
◦
atmosphere is stirred at 95 C. After 6 h the reaction mixture
was analyzed by HPLC.
HPLC Analysis
HPLC analysis was performed with a Summit Dual Gradient
HPLC system (Dionex) connected with a PDA3000 diode array
detector (Dionex). The HPLC was equipped with an Alltima HP
C18 3u reverse phase column (150 × 4.6 mm), with a flow rate of
−
1
Catalytic Allylation of BPA
1
ml min and an injection volume of 10 µl of a solution of the
reaction mixture in acetonitrile. The gradient conditions were at
t = 0–17 min acetonitrile (%) : water (%) = 50 : 50, t = 17–23 min
acetonitrile 100%, t = 23–30 min acetonitrile (%) : water (%) =
The results of the use of the most selective catalysts in the
O-allylation of BPA with allyl alcohol are given in Table 1. The ratio
BPA over catalyst used was 500 : 1 and therefore conversions of
5
0 : 50. Spectroscopic data for compounds 3–7 corresponded
1
(Scheme 2) after 1 h are higher compared with the reactions
[
2]
with those reported in literature.
with 4-tert-butylphenol reported previously, where a substrate
over catalyst ratio of 1000 : 1 was generally used. However, when
the number of OH moieties is considered, conversions of 4-
tert-butylphenol and BPA are similar. [RuCp(PPh3)2](OTs) in the
presence of acid (p-toluenesulfonic acid = HOTs) is reasonably
selective for O-allylation of BPA with a conversion of 46% of BPA
and a selectivity of 80% for O-allylation after 1 h (entry 1). This
selectivity is considerably lower than the selectivity for O-allylation
of 4-tert-butylphenol (>90%), which is most likely caused by the
fact that product 4 is only formed after two equilibrium reactions.
When allyl alcohol is replaced with diallyl ether as the allylating
Results and Discussion
Product Analysis
The main problem arising from the use of BPA as the substrate
is that a large number of different products can be formed
(
Scheme 2). In the allylation of 4-tert-butylphenol a total of four
products are observed, that are conveniently separated with
GC. In the allylation of BPA a total of 14 different products
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Copyright ꢀc 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 207–211

Selective O-allylation of bisphenol A
monoallylated products
bisallylated products
HO
OH
HO
HO
O
O
O
1
cat
3
4
+
OH
O
OH
HO
2
6
7
5
+
trisallylated products
+
HO
OH
H O
2
Scheme 2. Structures of mono- and bisallylated products 3–7 formed in allylation of BPA with allyl alcohol. Structures of possible trisallylated products
are not shown.
Table 1. Allylation of BPA using several catalytic systems and conditionsa
Conversion of 1(%)
(
selectivity for O-allylation, %)b
Allylating
agent
Temperature
Yield of 4
after 3 h (%)
◦
Entry
Catalytic system
( C)
1 h
3 h
1
[RuCp(PPh3)2](OTs)
[RuCp(PPh3)2](OTs)
allyl alcohol
diallyl ether
allyl acetate
allyl alcohol
allyl alcohol
allyl alcohol
allyl alcohol
60
60
46 (80)
91 (68)
81 (74)
22 (70)
62 (66)
80 (80)
38 (100)
46 (63)
98 (48)
90 (52)
31(50)
14
30
18
5
2
3
4c
[RuCp(PPh3)2](OTs)
60
[RuCp(PPh3)2](OTs)
60
5
[RuCp(dppb)](OTs)
80
89 (65)
81 (76)
54 (100)
20
25
10
6d
7e
[RuCp(PPh3)(resinPhPPh2](OTs)
Pd(OAc)2 + dppdmp
80
100
a
Reaction conditions: ratio BPA : allyl alcohol : [Ru] : AgOTs : HOTs = 500 : 2000 : 1 : 2 : 20, toluene.
b
c
Selectivity towards O-allylation indicated in parentheses. O-allylation = 3 + 4; C-allylation = 5–7 + trisallylated compounds.
n-Heptane was used as solvent.
d
e
Reaction conditions: ratio BPA : allyl alcohol : [Ru] : AgOTs : HOTs = 50 : 200 : 1 : 2 : 2, toluene.
◦
Reaction conditions: ratio BPA : allyl alcohol : Pd(OAc)2 : dppdmp = 500 : 2000 : 1 : 4, 100 C.
agent, the conversion of BPA is higher (entry 2). C-allylation
commences at an earlier stage during the reaction, due to the
higher initial conversion, since diallyl ether formation from allyl
alcohol is not occurring.
In the patents of Dow Chemicals,[1,9] allyl acetate is claimed to
The use of n-heptane as solvent results in significantly lower
conversion and selectivity (entry 4) compared with toluene. This
can be explained by the low solubility of BPA in n-heptane at
the reaction temperature. The desired products (3 + 4), however,
are soluble and therefore the reaction of these products into
the undesired C-allylated products is relatively rapid. The use of
be superior to allyl alcohol as an allylating agent. If allyl acetate
is used as the allylating agent in our reaction conditions (entry 3),
the catalyst is only active in the presence of p-toluenesulfonic acid,
most likely to form acetic acid and thus prevent the formation
of the relatively strongly coordinating acetate anion. Although
the use of allyl acetate with our catalytic system results in higher
activity, the overall selectivity for O-allylation decreases. In the
[RuCp(dppb)](OTs) as the catalyst (entry 5) gives relatively low
selectivity, but after 3 h reaction time this catalyst is slightly more
selective than [RuCp(PPh3)2](OTs) with high conversion. The use
of the immobilized Ru-catalyst (entry 6) gives a highly selective
reaction towards O-allylation and the catalyst was effectively
recovered (leaching 1% of total Ru-content on support). Finally,
Pd(OAc)2 in combination with the ligand dppdmp gives excellent
selectivity towards O-allylation (entry 7), but after 3 h mainly the
monosubstituted product 3 is formed and only 10% of the bisallyl
ether 4 is obtained.
The equilibrium reaction of O-allylation is controlled by the
amount of water that dissolves in the organic phase. Toluene is
beneficial to obtain a reasonable conversion; it is quite apolar and
thus the water solubility is low, but it is not too apolar for BPA
to dissolve at reaction temperature. A further benefit of the use
of toluene is that the desired product is completely soluble at
room temperature; as the starting material BPA is not soluble it
conveniently crystallizes from the reaction mixture in high purity,
thus allowing recovery of the starting material from the reaction
products.
[
1,9]
reactions described in the Dow patents,
[RuCpCl(PPh3)2] is
used as the catalyst, but a very high catalyst concentration
is used (2 mol%) and the selectivity is not reported in a clear
manner. Most likely the phenol content was determined by means
of titration of the phenol residues, which makes it impossible
to determine the amount of C-allylation. When such a patent
experiment is reproduced (see Experimental section), the analysis
results of our HPLC method show that the selectivity for O-
allylation is rather low (41%) and a large amount of trisallylated
product is obtained (52%). The use of allyl acetate thus results
in lower selectivity for O-allylation and we therefore conclude
that allyl alcohol or diallyl ether remain the more attractive
allylating agents.
Appl. Organometal. Chem. 2011, 25, 207–211
Copyright ꢀc 2010 John Wiley & Sons, Ltd.
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J. A. van Rijn et al.
Table 2. Allylation of BPA in the presence of Ru- or Pd-based catalysts with different solvent systemsa
Conversion of
1
(%) (selectivity for O-allylation, %)b
Entry
Catalyst
Solvent
1 h
3 h
Yield of 4 after 3 h (%)
+
+
+
+
+
+
+
+
1
2
3
4
5
6
7
8
9c
[RuCp(PPh3)2]
[RuCp(PPh3)2]
[RuCp(PPh3)2]
[RuCp(PPh3)2]
[RuCp(PPh3)2]
[RuCp(PPh3)2]
[RuCp(PPh3)2]
[RuCp(PPh3)2]
Allyl alcohol
0 (−)
47 (100)
86 (85)
95 (81)
96 (68)
55 (91)
80 (92)
78 (93)
12 (100)
0 (−)
54 (94)
95 (82)
95 (72)
96 (64)
80 (86)
98 (84)
90 (88)
28 (100)
0
9
Diallyl ether (DAE)
DAE : toluene = 2 : 1
DAE : toluene = 1 : 1
DAE : toluene = 1 : 2
DAE : heptane = 2 : 1
DAE : heptane = 3 : 1
DAE : heptane = 4 : 1
DAE : toluene = 2 : 1
50
51
46
23
49
38
Pd(OAc)2 + dppdmp
2 (24)
a
◦
Reaction conditions: ratio BPA : allyl alcohol : [RuCpCl(PPh3)2] : AgOTs : HOTs = 500 : 2000 : 1 : 2 : 20, 60 C, total solvent volume = 2.5 ml.
Selectivity towards O-allylation indicated in brackets. O-allylation = 3 + 4; C-allylation = 5–7 + trisallylated compounds.
b
c
◦
Reaction conditions: ratio BPA : allyl alcohol : Pd(OAc)2 : dppdmp = 500 : 2000 : 1 : 4, 100 C, total solvent volume = 2.5 ml. Yield of 4 in parentheses
determined after 20 h reaction time. Selectivity for O-allylation remains 100%.
Allylating Agents as Solvent
be considered. Owing to the thermodynamic preference of C-
allylation over O-allylation of phenols, the reaction eventually will
build up C-allylated side products, of which the concentration
depends on a combination of catalyst structure and reaction time
and is independent on the allylating agent. It is therefore of key
importance that the reaction is halted before C-allylated products
form when performed in a batch reaction. In a continuous process
both water, forming a separate phase in the reaction mixture,
and the desired product needs to be efficiently removed from
the reaction mixture while feeding it with new starting materials.
The very low polarity of product 4 compared with 1 and water
could be used to separate these compounds by extraction. Diallyl
ether should be used as (co-)solvent, which can be efficiently
synthesized from allyl alcohol; with the use of [RuCp(PPh3)2](OTs)
The reaction with [RuCp(PPh3)2](OTs) as the catalyst in the
presence of acid and with diallyl ether as the allylating agent gave
the highest yield of 4 (30% after 3 h). The selectivity for O-allylation
is, however, not very high and a large amount of C-allylated
products is formed. In an attempt to improve the selectivity of
the reaction, different solvent systems were investigated and the
results are shown in Table 2.
When the reaction is performed in allyl alcohol as the solvent,
no conversion of 1 is observed (entry 1) and only formation of
diallyl ether is detected. With diallyl ether as the solvent (entry
2), the reaction proceeds very selectively, but mainly product 3
is formed and only 9% of 4 is formed after 3 h reaction time.
When the reaction medium is made more apolar by using a
mixture of diallyl ether and toluene (entry 3), conversion of 1
and yield of 4 is increased in a major way and 50% of 4 (based
on 1) is formed, a very high yield for a product that is formed
via two equilibrium reactions. Making the solvent more apolar
by increasing the amount of toluene on diallyl ether causes a
decrease in selectivity (entries 4 and 5). Also n-heptane was used
as the apolar component in the reaction mixture. When the results
from entries 6–8 are compared with that of entry 3, it appears that
slightly less n-heptane than toluene should be used for an optimal
selectivity for O-allylation, which obviously can be related to the
+
HOTs as the catalytic system, extremely high turnover numbers
can be achieved based on allyl alcohol (>200 000), as has already
been demonstrated.[
16]
A schematic representation of a possible continuous process is
shown in Fig. 2. In an ideal case, diallyl ether should be synthesized
from pure allyl alcohol, catalyzed by the Ru-catalyst, forming only
water as co-product (reactor 1: R1 in Figure 2). The resulting
mixture is then separated in a separation system (S2); a suitable
method would be distillation. The isolated diallyl ether is used
as allylating agent (in excess) in the O-allylation of BPA (reactor
2, R2), catalyzed by the same catalyst present in reactor 1. An
inert solvent (like n-heptane) could be added during, but also
after, the reaction to create an apolar system from which the
phenolic products and catalyst would precipitate, occurring in
S2. This separation is believed to be the bottleneck of such a
process, since many compounds are present in the mixture from
R2 and in particular products 3 and 4 proved to be difficult to
separate. A bleed of C-allylated products would be necessary, in
order to prevent accumulation of these compounds. However, the
catalystshouldberecycledandthereforeaheterogeneouscatalyst
would be favored.[ If the catalyst was homogeneous, it would
also be removed from the process, which is only commercially
acceptable when the bleed is very small or the catalyst is highly
active with high turnover numbers. Compounds containing two
phenol moieties hardly dissolve in heptanes and are therefore
less difficult to retrieve from the reaction mixture. However, the
selective separation of C-allylated product from 3 is expected to be
+
lower polarity of n-heptane. Finally, besides the [RuCp(PPh3)2]
catalyst, the Pd-containing catalytic system proved to be highly
selective for O-allylation. When a diallyl ether–toluene mixture
is used as the solvent, the reaction is completely selective for
O-allylation; however, conversion of BPA after 3 h is considerably
lower than in the Ru-based catalytic system. After 20 h, only O-
allylated products are detected while the yield for 4 increases to
2
4% based on 1. Longer reaction times did not result in higher
conversion, indicating complete deactivation of the catalyst. This
deactivation also prevents possible C-allylation, as C-allylation
mostly occurs to an appreciable extent later in the reaction, when
a high concentration of O-allylated product is reached.
18]
Industrial Application
When the described allylation reaction with BPA as the substrate
is implemented in an industrial process, several things should
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Copyright ꢀc 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 207–211

Selective O-allylation of bisphenol A
heptane
heptane
heptane
H O
+
2
4
R1
S1
R2
S2
S3
DAE
4
2
[Ru] + 3
1
C-allylated products
(recycled)
2
Figure 2. Schematic overview of a possible process for the catalytic allylation of bisphenol A. DAE = diallyl ether. R = reactor; S = separation system.
very difficult. Finally, heptanes are removed from the the bisallyl
ether of BPA by means of distillation in separation system 3 (S3).
and Dr J. K. Buijink (Shell Global Solutions International BV) for
fruitful discussions. Mr J. A. P. P. van Dijk is kindly acknowledged
for assistance with the HPLC analyses.
Conclusions
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2
[
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Also the challenging epoxidation reaction
performed to obtain the final epoxy resin component makes
further research necessary.
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Acknowledgment
This work was supported by the Technology Foundation STW. We
would like to thank Dr R. Postma (Hexion Specialty Chemicals)
Appl. Organometal. Chem. 2011, 25, 207–211
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