Synthesis of dichlorophenylphosphine via a Friedel-Crafts reaction in [Et4N]Br-XAlCl3 ionic liquids

Article abstract of DOI:10.1080/104265090930407

The Friedel-Crafts reaction of phosphorus trichloride and benzene in [Et₄N]Br-XAlCl₃ ([Et₄N]Br = tetraethylammonium bromide) ionic liquids (ILs) was investigated for the clean synthesis of dichlorophenylphosphine (DCPP). A simple product isolation procedure was achieved, and the effects of IL's composition, reaction time, and quantity on this reaction were studied. The [Et₄N]Br-XAlCl₃ ILs gave this reaction a green character. From the isolation experiments, it was found that (a) because of the formation of the complex of DCPP and AlCl₃, the catalytic activity of the [Et₃NH]Cl-XAlCl₃ ([Et ₃NH]Cl = triethylhydrogenamonium chloride) was reduced; (b) with the addition of quaternary ammonium to the IL's residue, additional DCPP could be recovered. Copyright Taylor & Francis Inc.

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Phosphorus, Sulfur, and Silicon
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Synthesis of
Dichlorophenylphosphine via
a Friedel-Crafts Reaction in
[
Et N]Br-XAlCl Ionic Liquids
4 3
a
a
a
Yu-Yong Wu , Li-Sheng Wang & Zhong-Wei Wang
a
School of Chemical and Environment Engineering,
Beijing Institute of Technology, Beijing, People's
Republic of China
Published online: 19 Aug 2006.
To cite this article: Yu-Yong Wu , Li-Sheng Wang & Zhong-Wei Wang (2005): Synthesis
of Dichlorophenylphosphine via a Friedel-Crafts Reaction in [Et N]Br-XAlCl Ionic
4
3
Liquids, Phosphorus, Sulfur, and Silicon and the Related Elements, 180:12, 2667-2677
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Phosphorus, Sulfur, and Silicon, 180:2667–2677, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090930407
Synthesis of Dichlorophenylphosphine
via a Friedel-Crafts Reaction in [Et N]Br-XAlCl
4
3
Ionic Liquids
Yu-Yong Wu
Li-Sheng Wang
Zhong-Wei Wang
School of Chemical and Environment Engineering,
Beijing Institute of Technology, Beijing, People’s Republic of China
The Friedel-Crafts reaction of phosphorus trichloride and benzene in [Et N]Br-
4
XAlCl ([Et N]Br = tetraethylammonium bromide) ionic liquids (ILs) was inves-
3
4
tigated for the clean synthesis of dichlorophenylphosphine (DCPP). A simple prod-
uct isolation procedure was achieved, and the effects of IL’s composition, reaction
time, and quantity on this reaction were studied. The [Et N]Br-XAlCl ILs gave
4
3
this reaction a green character. From the isolation experiments, it was found that
a) because of the formation of the complex of DCPP and AlCl , the catalytic ac-
(
3
tivity of the [Et NH]Cl-XAlCl ([Et NH]Cl = triethylhydrogenamonium chloride)
3
3
3
was reduced; (b) with the addition of quaternary ammonium to the IL’s residue,
additional DCPP could be recovered.
Keywords Dichlorophenylphosphine; Friedel-Crafts reaction; ionic liquids; clean
synthesis
INTRODUCTION
Dichlorophenylphosphine (DCPP) is a commercially important com-
pound in organic synthesis and it is widely used in the preparation
of flame-retardants, insecticides, stabilizers, plasticizers, and antioxi-
dants. It can be prepared by an aluminum trichloride (AlCl3)-catalyzed
1
Friedel-Crafts reaction of benzene with PCl3. However, there exist
problems in the preparation procedure. Because of the formation of
complex of AlCl3 and DCPP in the reaction, a stoichiometric or excess
amount of AlCl3 is needed and it makes the DCPP difficult to be iso-
lated. In those modified methods,2 POCl3, pyridine, or water were
−5
Received September 14, 2004; accepted December 18, 2004.
Address correspondence to Li-Sheng Wang, Beijing Institute of Technology, School
of Chemical and Environment Engineering, Beijing 100081, People’s Republic of China.
E-mail: lishengwang@btamail.net.cn
2667

2
668
Y.-Y. Wu et al.
added to breakdown the complex, and then the DCPP was extracted
using organic solvents for the isolation of the product. This procedure
adds the to cost and need for more industrial procedures. The non-
reusable and large quantity of a catalyst would form a great amount of
solid waste, which is difficult to handle and can greatly contaminate the
environment. Moreover, in the extraction procedure, a large quantity of
organic solvents is needed, which is another source that contaminates
the environment. Therefore, there is a strong incentive to find clean
synthesis and simple product isolation procedures in the preparation of
DCPP.
Ionic liquids (ILs) exhibit various advantages in organic reactions.6−9
The designable ILs possesses green characters: They are free of volatile
organic compounds (VOCs); they are readily recycled; and they have
profound effects on the activity and selectivity in reactions. In most
cases of the Friedel-Crafts reactions, the using of aluminate ionic liquids
facilitates the isolation of products.
In a previous report,10 we found [BuPy]Cl-XAlCl3 ([BuPy]Cl = N-
butylpyridinium chloride; X is the mole ratio of AlCl3 in the [BuPy]Cl
and AlCl3 system) ionic liquid could catalyze the Friedel-Crafts reaction
of PCl3 and benzene, and render this reaction some cleaner characters,
such as less catalyst consumption, convenient catalyst recovery, and
product isolation. After the reaction, the mixture was homogeneous
at room temperature; the DCPP was extracted using petroleum ether
1
1
that was immiscible with the ILs. In an alternative report, we used
Et3NH]Cl-XAlCl3 ([Et3NH]Cl = triethylhydrogenammonium chloride;
[
X is the mole ratio of AlCl3 in the [Et3NH]Cl and AlCl3 system) ionic
liquid to catalyze the same reaction, and, in this case, we found that
at a high temperature, the reaction mixture was almost homogeneous;
after the reaction, the mixture was cooled to room temperature. It sepa-
rated into a diphase system. Part of the DCPP could be separated from
the PCl3 layer directly by distillation, and another part was extracted
from the ILs layer using petroleum ether as solvent. These experiments
demonstrate that the solvent properties had been changed with the
changing of the molecular structure of the cation. Moreover, we found
that for the IL’s phase in the both cases, after the recovery of petroleum
ether by vacuum distillation, the weight of the IL’s residue was obvi-
ously increased because of the formation of the complex of DCPP and
AlCl3. From a point of view of the product isolation and the catalyst or
raw materials recycling, this reaction needs to be improved.
This article is our continuous study of ILs catalyzed reaction of PCl3
and benzene. The reaction characters of PCl3 and benzene using an-
other ILs [Et4N]Br-XAlCl3 ([Et4N]Br = tetraethylammonium bromide;
X is the mole ratio of AlCl3 in the [Et4N]Br and AlCl3 system), as

Synthesis of Dichlorophenylphosphine
2669
catalyst was investigated.
[
Et
4
N]Br-XAlCl
3
PCl3 + Ph-H −− −−−−−−−−−−−−−−−−−→ PhPCl2
(1)
The effects of changing the anion on the catalyst recycling and prod-
uct isolation will be investigated in this article. The effects of acidity
(
different X values), the amount of the [Et4N]Br-XAlCl3 ILs, and the
effects of reaction time and reactant composition on this reaction will
be studied as well. A more convenient isolation procedure from the re-
action mixture successfully is achieved and the separation of the DCPP
from the ILs was compared with the separation from complex AlCl3·
DCPP.
EXPERIMENTAL
Aluminum chloride, phosphorus chloride, triethylhydrogenammo-
nium chloride ([Et3NH]Cl), tetraethylammonium bromide ([Et4N]Br),
◦
petroleum ether (60–90 C), and benzene were analytical reagents from
VAS Chemical Reagent Corporation Ltd. in Beijing, China. [Et3NH]Cl-
AlCl3 ionic liquids were prepared according to the previous procedure
we described.
To ensure reaction conditions were free of water, the preparation
of ILs and the Friedel-Crafts reaction were carried out in a nitrogen
atmosphere.
Preparation of [Et N]Br-XAlCl and [Et NH]Cl-XAlCl (X = 2) ILs
4
3
3
3
In a round-bottomed flask equipped with a magnetic stirrer and a gas in-
let valve, 26.7 g (0.2 mol) of anhydrous AlCl3 was slowly added to 21.0 g
(
3
0.1 mol) of tetraethylammonium bromide. The mixture was stirred for
h to ensure a complete reaction, and reduced pressure (13.3 kPa) was
used to remove the possible evaporate impurities.
Similarly, to prepare a [Et3NH]Cl-2AlCl3 ionic liquid, 0.2 mol an-
hydrous AlCl3 was slowly added to 0.1 mol triethylammonium hydro-
gen chloride, and the mixture was stirred for 3 h to ensure a complete
reaction.
Other compositions of [Et4N]Br-XAlCl3 and [Et3NH]Cl-XAlCl3 (X =
1
, 1.5, 2.5 mole ratio of AlCl3) were prepared according to this procedure,
with appropriate amounts of AlCl3, tetraethylammonium bromide, and
triethylammonium hydrogen chloride (for example, 0.1 mol AlCl3 and
0
.1 mol [Et4N]Br for X = 1; 0.15 mol AlCl3 and 0.1 mol [Et4N]Br for X =
1.5; 0.25 mol AlCl3 and 0.1 mol [Et4N]Br for X = 2.5).

2
670
Y.-Y. Wu et al.
General Friedel-Crafts Reaction Procedure
In a round-bottomed four-necked flask equipped with a stirrer, a con-
denser, and a gas inlet valve, the designed amount of PCl3 and benzene
were added to a weighed quantity of [Et4N]Br-XAlCl3. The mixture was
heated and refluxed for the scheduled number of hours. Then the mix-
◦
ture was cooled to about 20 C and phase separation could be observed.
The lower layer was viscous IL and the upper layer was a mixture of
PCl3, benzene, and DCPP. The product DCPP in the lower layer was
1
1
recovered in a similar way as described in our previous article. Ex-
tract the DCPP in the ILs with petroleum and then get the product
at reduced pressure. The PCl3 and benzene in the upper layer was re-
moved by distillation at atmospheric pressure, followed by distillation
◦
at a slightly reduced pressure (6.67 kPa) below 90 C. The DCPP was
◦
distilled in vacuum with a boiling point of 92–94 C/1.56 kPa (literature
0–92 C/1.33 kPa, 68–70 C/0.133 kPa, 94 C/1.60 kPa) density d30
◦
14
◦
14
◦
12
9
1
14
13
.3576–1.3682 (literature, d25 1.327 g/mL, d30.9 1.3567 g/mL), vis-
1
3
cosity η30 3.01 mPa·s (literature η29.45 2.99 mPa·s), refraction index
2
5
25
14
n
1.5910–1.5914 (literature n 1.5912). Gas chromatographic anal-
D
D
ysis (GC-14C gas chromatograph) showed that the purity of DCPP was
above 96.0%.
3
Preparation of Complex AlCl ·DCPP and the Isolation of DCPP
From the Complex of DCPP and AlCl3
The complex used for the DCPP isolation experiments was prepared by
mixing DCPP with an equal molar of AlCl3. The mixture was kept at
◦
7
0 C for 2 h. To 62.4 g (0.2 mole) of the complex prepared above was
added to 27.5 g (0.2 mole) and [Et3NH]Cl (the reaction is exothermic
and the [Et3NH]Cl should be added in portions), and the mixture was
◦
kept at about 70 C for 2 h. DCPP was extracted with petroleum ether
or PCl3 and isolated in a similar way as in the above general procedure
to prepare DCPP. In other cases, the above procedure was repeated,
except for replacing the [Et3NH]Cl with an equimolar of [Et4N]Br.
RESULTS AND DISCUSSIONS
Isolation of DCPP From the [Et N]Br-XAlCl Catalyzed
4
3
Reaction Mixture
A more convenient product isolation procedure was achieved and the
amount of the complex of DCPP and AlCl3 in the ionic liquid residue
was reduced. Because there exists an excess amount of PCl3, the

Synthesis of Dichlorophenylphosphine
2671
reaction mixture was separated into a diphase system. Although PCl3 is
extremely soluble in the ionic liquid, the reverse is not the case, with no
appreciable IL solubilization in the PCl3 phase. Therefore, the leaching
of a catalyst into the PCl3 phase can be minimized. The product DCPP
could be isolated without using any other organic solvent, which is more
convenient in industrial processes, compared with classical methods,
and makes the PCl3 and benzene readily to be recycled. In all cases, the
yields of DCPP isolated from the reaction mixture ranged from 46–60%
(
based on benzene).
Catalytic Activity of [Et N]Br-XAlCl Ionic Liquids
4
3
Reaction cases using various amounts of IL’s with different IL’s composi-
tions (a different X value in [Et4N]Br-XAlCl3 ionic liquids) were carried
out to investigate the catalytic activity of [Et4N]Br-XAlCl3 ILs in the
reaction of PCl3 and benzene. The results are summarized in Table I.
−
From Table I we can find that [AlCl3Br] does not catalyze the reaction
(
when X = 1) and excess AlCl3 is needed to catalyze the reaction. Thus,
the acidic (X > 1) [Et4N]Br-XAlCl3 ILs showed fair catalytic activity
in the reaction, and the catalytic activity increased as their acidity in-
creased. Those basic (X = 0.67) and neutral (X = 1) [Et4N]Br-XAlCl3
ILs, however, showed nearly no catalytic activity. These results agree
with those discovered Friedel-Crafts reactions catalyzed by other ILs.
The most interesting result in these cases is that the ILs could be used
1
1
TABLE I Catalytic Activity of [Et
4
N]Br-XAlCl
3
ILs. Reactions were Carried out with
Refluxing for 6 h
X
PCl3:benzene:ILs/mole ratio
Yield/%
0
1
2
2
2
1
1
2
2
2
2
1
2
2
.67
4:2:1
4:2:1
4:2:1
3.2
5.4
23.6
44.0
50.4
49.6
46.9
51.2
55.4
55.1
59.9
24.8
27.2
19.5
8:4:1
16:8:1
30:10:1
30:15:1
30:15:1
30:15:1
30:10:1
30:10:1
60:30:1
60:30:1
60:30:1
.5
.5
.2
.2
.5
.2

2
672
Y.-Y. Wu et al.
in catalytic quantity. Thus, a yield of 51.2% was obtained in the case
with the 30:15:1 mole ratio of PCl3:benzene:ILs (X = 2). We were inter-
ested to find that when the ionic liquids used in a catalytic amount (a
mole ratio of benzene:ILs exceed 10:1), the amount of product isolated
showed a direct ratio to the amount of the ILs. When a large amount of
ionic liquids were used, the yields decreased.
Compared with the normal method to prepare DCPP using AlCl3 as
a catalyst, which was near 80%, the yield using ionic liquids is fairly
lower. However, in the normal system, the catalyst consummation is
much more, compared with the IL’s catalyzed reaction. From a point of
view of reactant recycling, the unreacted benzene and PCl3 are easily
recovered by simple evaporation after the reaction and the phase sepa-
ration, while the AlCl3 is wasted after the reaction, and the AlCl3 takes
the most expense in the production of DCPP. If we define a quantity (C)
to represent how much moles of DCPP are produced with one mole of
AlCl3, we can find that, in the normal process using AlCl3 as catalyst,
this quantity is always less then its unity. However, when using ILs
as a catalyst, this quantity is larger than its unity. From Table II, it
is clear that the cost of using a normal AlCl3 as a catalyst can be five
times as high than using ILs as catalyst; and the contamination must
also be five times reduced by using ILs. Thus, use of ILs as a catalyst
has the advantage of less catalyst consumption, and, therefore, brings
out less waste, which makes it interesting.
Effects of Reactant Composition and Reaction Time
The effects of reactant composition and reaction time on the reaction of
PCl3 and benzene using a catalytic quantity of [Et4N]Br-XAlCl3 were
TABLE II Effects of Reactant Composition and
Reaction Time
PCl3:benzene:
a
ILs/mole ratio
Reaction time/h
Yield/%
C.
3
0:10:1
0:10:1
0:10:1
0:15:1
0:15:1
0:15:1
0:30:1
0:30:1
0:30:1
4
6
8
4
6
10
6
10
16
48.8
55.1
56.6
44.5
51.2
53.1
27.2
29.3
28.1
2.44
2.76
2.83
3.34
3.84
3.98
4.08
4.40
4.22
3
3
3
3
3
6
6
6
aILs: [Et4N]Br-2AlCl3.

Synthesis of Dichlorophenylphosphine
2673
investigated, and the results were summarized in Table II. From Ta-
ble II, we found that the yields showed a slightly increased trend when
the mole ratio of PCl3:benzene increased. Six hours would be enough for
the reaction to be complete, and a longer time than that did not show as
apparent increase of the yields. Thus, with a catalytic quantity of ILs,
the mole ratio of PCl3:benzene:ILs (X = 2) is 30:15:1; when the reaction
time is 4 h, a yield of 44.5% is obtained, while when the reaction time
is 6 h, the yield is 51.2%, and when the reaction time is 10 h, the yield
is 53.1%.
Reusable Character of the [Et N]Br-XAlCl ILs
4
3
The catalytic amount of ILs was isolated and used directly in the fol-
lowed runs to investigate their reusable characters. From Table III,
we found that the ILs still showed catalytic activity in the runs that
followed, but the catalytic activity quickly decreased. Thus, a yield of
5
1.2% was obtained in the first run (with PCl3:benzene:ILs (X = 2),
equals to 30:15:1), and yields of 24.3% and 6.1% were obtained, respec-
tively, in the following reactions when the ILs were reused. After the re-
action, there is some yellow solid in the ropy ionic liquids residues, and
unlike that in the [Et3NH]Cl-XAlCl3-catalyzed reactions, the weight of
the [Et4N]Br-XAlCl3 residues did not increased.
Isolation of DCPP From the Complex DCPP·AlCl and the Ionic
3
Liquid Residues
In both the [Et3NH]Cl-XAlCl3 and [Et4N]Br-XAlCl3, ionic liquids cat-
alyzed reactions of PCl3 and benzene; the reactions could be carried
out with a catalytic amount of catalyst, but the catalytic activity was
TABLE III Reusable Characters
of [Et N]Br-2AlCl Ils
4 3
PCl3:benzene:
ILs/mole ratio
aRuns
Yield/%
3
3
3
3
3
3
0:15:1
0:15:1
0:15:1
0:10:1
0:10:1
0:10:1
1
2
3
1
2
3
51.2
24.3
6.1
48.8
28.5
12.6
aReactions were carried out with
refluxing for 6 h.

2
674
Y.-Y. Wu et al.
TABLE IV Comparisons of the Coordination Properties for the Two
Kinds of IL: Isolation of DCPP by Extraction the Complexes With
Solvents and the Recovery of DCPP by Distillation at a Reduced
Pressure
Recovery of
Case no.
Case 1
Complex
DCPP AlCl3
Extraction procedure
DCPP, %
Extraction with petroleum
ether
Extraction with PCl3
Extraction with PCl3; phase
separation; then extraction
the ILs phase with
0a
Case 2
Case 3
DCPP·AlCl3
0a
a
ILs + DCPP (ILs =
38
[
Et3NH]Cl-2AlCl3, with
AlCl3:DCPP molar ratio =
:1)
ILs + DCPP (ILs =
Et4N]Br-2AlCl3, with
AlCl3:DCPP molar ratio =
:1)
1
petroleum ether
Case 4
Extraction with PCl3; phase
separation; then extraction
the ILs phase with
petroleum ether
Extraction after addition of
Et3NH]Cl
Extraction after addition of
Et4N]Br
79a
[
1
Case 5
Case 6
[Et3NH]Cl-2AlCl3 residue
>62b
[
[Et4N]Br-2AlCl3 residue
0b
[
aThe recovery of DCPP is calculated based on the DCPP used in the preparation of
complex.
bThe recovery of DCPP is calculated based on the weight increase of the IL residue
after each reaction.
reduced as they were recycled. The reason for the reduction of the cat-
alytic activity is complicated. Decomposition and leaching of the cata-
lyst into the solvent phase might take place during the reaction and
separation process. Nevertheless, this is not obvious, as shown by the
experimental data in Table IV. In fact, the coordination property of
the ionic liquid can be changed with the changing of anion. Table IV
lists the comparisons of the coordination properties for the two kinds
of ionic liquid. In the experimental cases 1 and 2 in Table IV, a compar-
ison for the extraction ability of petroleum ether or PCl3 for the DCPP
from the complex AlCl3·DCPP was made. The complex (AlCl3·DCPP)
was used for the DCPP isolation and was prepared by mixing an equal
molar of DCPP with AlCl3. The results, which are listed in Table IV,
show that there was no DCPP that could be extracted directly. In cases
3
and 4, same amount of DCPP was added at first to the two kinds
of ILs, respectively. Then, DCPP could be isolated by extracting the
two kinds of complex with an equal amount of solvent and by distilla-
tion at reduced pressure. A comparison can be made for the recovery
of DCPP that was calculated based on the initial amount DCPP used

Synthesis of Dichlorophenylphosphine
2675
in the preparation of complex. From the experimental data, it is clear
that the coordination of DCPP with the [Et3NH]Cl-XAlCl3 ionic liquid
is stronger than the coordination of DCPP with the [Et4N]Br-XAlCl3
ionic liquid. For case 4, the DCPP recovery is 79%, while for case 3, it
is only 38%. This agrees with the evidence that with the use of the new
catalyst, the weight of the ILs residue was scarcely increased after the
reaction.
In subsequent experiments, the reaction residues from the above
two kinds of ionic liquid ([Et3NH]Cl-XAlCl3 and [Et4N]Br-XAlCl3) were
treated with quaternary ammonium, respectively, to show if there ex-
ists complex AlCl3·DCPP in them. The complex can be broken by the
addition of quaternary ammonium with the following AlCl3-consuming
reactions:
−
−
[
AlCl4] + AlCl3 → [Al2Cl7]
(2)
(3)
(4)
+
−
AlCl3 + [Et3NH]Cl → [Et3NH] + [AlCl4]
AlCl3 + [Et3NH][AlCl4] → [Et3NH] + [Al2Cl7]
AlCl3·DCPP + [Et3NH]Cl → [Et3NH] + [AlCl4] + DCPP (5)
AlCl3·DCPP + [Et3NH][AlCl4] → [Et3NH] + [Al2Cl7] + DCPP (6)
−
+
−
+
−
−
+
−
Here we assume that there may exist complex AlCl3·DCPP in the
IL’s catalyzed reactions, which may contribute to the weight increase of
the residues and the reduction of the catalytic activity. In case 5, there
was 62% DCPP isolated from the [Et3NH]Cl-XAlCl3 IL residue (the
recovery of DCPP was calculated based on the weight increase of the IL
residue after the Friedel-Crafts reaction). It indicated that there does
exist a complex of AlCl3 and DCPP in the residues, and the addition
of quaternary ammonium can make the DCPP isolated. The formation
of the complex of AlCl3 and DCPP in the IL’s residues consumed part of
the AlCl3, which changed its acid/base character. This may explain the
results obtained from the [Et3NH]Cl-XAlCl3 catalyzed reactions, that
the ionic liquids were recyclable with reduced catalytic activity.
In case 6, using [Et4N]Br as a comparison with case 5, there was no
DCPP isolated from the [Et4N]Br-XAlCl3 IL’s residue. This tendency
agrees with the result in case 4 (the coordination of DCPP with the
[
Et4N]Br-XAlCl3 ionic liquid is weak, so that after extraction, there is
little DCPP remaining in the residue), and it shows how the coordina-
tion property of the ILs is effected by the different anions.
In another one of our articles,15 the IL was used to catalyze the re-
action of DCPP with sulfur to produce dichloride phosphinic sulfide
(
DCPPS). It was found that the ILs catalyst could be recycled many
times without losing activity. Thus, in this article, the remaining part

2
676
Y.-Y. Wu et al.
of DCPP existed as a complex state in the IL’s residues and reacted with
sulfur at first, then, the produced DCPPS was extracted with petroleum
ether. Separation for the petroleum ether phase allowed the IL catalyst
to be regenerated.
CONCLUSIONS
1
2
3
. The Friedel-Crafts reaction of PCl3 and benzene was carried out
in this work. Instead of using AlCl3 as a catalyst, the adduct of
AlCl3 with ammonium salt ([Et4N]Br-XAlCl3 ILs) was used as a
catalyst. Compared with the classical methods to prepare DCPP, the
reaction using [Et4N]Br-XAlCl3 ILs as catalyst exhibited a simple
product isolation procedure and less catalyst consumption, and the
unreacted raw materials could be reusable, which will contribute to
the clean synthesis of DCPP.
. From special extraction experiments, it was found that some DCPP
do exist in the [Et3NH]Cl-XAlCl3 residues, and to treat the reac-
tion residue of the IL phase with [Et3NH]Cl quaternary ammonium
is helpful to isolate the DCPP. Through the experiment by extrac-
tion of DCPP from the ionic liquid residue, it was shown that there
−
is less DCPP complex with anion of Al2Cl6Br . The effect of the
changing anion on the catalyst recycling and product isolation is
obvious.
. For the reaction catalyzed with an acidic AlCl3 IL to produce DCPP,
the yield that was achieved cannot reach the level with normal
AlCl3 as a catalyst. However, from a point of view of reactant re-
cycling, when comparing a yield of how much moles of DCPP are
produced with one mole AlCl3, using ILs as a catalyst has an ad-
vantage of less catalyst consumption, and, therefore, brings out less
waste.
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