Antimony(V) chloride-benzyltriethylammonium chloride complex as an efficient catalyst for friedel-crafts acylation reactions

Article abstract of DOI:10.1002/adsc.200303233

A novel catalytic system, the complex of antimony(V) chloride (SbCl ₅) and benzyltriethylammonium chloride (TEBA), C₆H ₅CH₂NEt₃(SbCl₅)₂Cl complex, is described for Friedel-Crafts acylation reactions of aromatics with acyl and sulfonyl chlorides. The catalyst has a number of useful characteristics, such as ready access, minimal toxicity, reusability, insensitivity to atmosphere and moisture, rapid acylation with high yield, and ease of operation.

Full text of DOI:10.1002/adsc.200303233

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Antimony(V) Chloride-Benzyltriethylammonium Chloride
Complex as an Efficient Catalyst for FriedelꢀCrafts Acylation
Reactions
An-ping Huang,a Xue-yuan Liu,a Lian-hua Li,a Xiao-li Wu,a Wei-min Liu,b
Yong-min Lianga, b,*
a
National Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. China
Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
b
Lanzhou 730000, P. R. China
Phone: (þ86)-931-8912593, fax: (þ86)-931-8912582, e-mail: liangym1@hotmail.com
Received: December 12, 2003; Accepted: April 15, 2004
Abstract: A novel catalytic system, the complex of
antimony(V) chloride (SbCl5) and benzyltriethylam-
monium chloride (TEBA), C6H5CH2NEt3(SbCl5)2Cl
complex, is described for Friedel Crafts acylation re-
actions of aromatics with acyl and sulfonyl chlorides.
The catalyst has a number of useful characteristics,
such as ready access, minimal toxicity, reusability, in-
sensitivity to atmosphere and moisture, rapid acyla-
tion with high yield, and ease of operation.
ammonium chloride SbCl5-TEBA complex, which has
many advantages, such as ready access, minimal toxicity,
reusability, insensitivity to atmosphere and moisture,
rapid acylation with high yield, and ease of operation.
It catalyzes Friedel Crafts acylation reactions smoothly
as shown in Scheme 1.
The acylation of anisole with acetyl chloride using the
complex of SbCl5 and TEBA as catalyst was investigated
as an initial model reaction (Table 1).
It can be seen from Table 1 that three catalysts all have
catalytic activity for the acylation of anisole, but the ac-
tivity of the complex BnNEt3(SbCl5)2Cl is the best of all.
Nitromethane was found to be a suitable solvent for this
catalytic system. These acetylation reactions were also
sensitive to the type of catalysts and anionic ligands,
that have been proved to be critical for high yields in
Keywords: antimony(V) chloride; benzyltriethylam-
monium chloride; catalysis; Friedel Crafts acylation
reactions; Lewis acids
The Friedel Crafts acylation reaction is a useful proce-
dure for forming carbon-carbon bonds on aryl rings,
and is a common procedure in organic synthesis as
well as in the chemical industry.[1] The basic operation
of the Friedel Crafts acylation and related reactions re-
quires the addition of a Lewis acid as catalyst, such as
metal chloride[2] (AlCl3, SbCl5, BF3, FeCl3, BiCl3, TiCl4
and SnCl4), which is often strongly oxyphilic. Addition-
ally, some other systems containing triflic acid[3] and lith-
ium perchlorate[4] have been also reported for such reac-
tions.[5] Various acylation operating conditions using
transition metals (In,[6], Hf,[3a,5c,7] Ag,[8] and Ga[9]) as cat-
alysts have been reported recently. But these catalysts
are generally expensive and require long reaction times
to complete the transformation, although the yield of
product is satisfactory. Since the Friedel Crafts acyla-
tion has unlimited potential for generating novelaryl de-
rivatives, alternative catalysts for this type of reactions
are desirable, which can be chosen for specific goals in
terms of reaction time, yield, substrate scope, catalyst
turnover, and operational practicability.
Scheme 1.
Table 1. Reaction conditions for the acetylation of anisole.[a]
Entry
Catalyst [5% mol]
T [8C][b]
Time
[min]
Yield
[%][c]
1
2
3
4
5
6
7
BnNEt3AlCl4
BnNEt3SbCl6
BnNEt3SbCl6
BnNEt3(SbCl5)2Cl
BnNEt3(SbCl5)2Cl
BnNEt3(SbCl5)2Cl
BnNEt3(SbCl5)2Cl
rt
rt
120
rt
40
80
120
120
20
120
60
<10
17
25
38
57
30
20
64
96
120
[a]
All reactions were carried out in nitromethane with the
substrates ratio: anisole/MeCOCl/catalyst¼ 2/1/0.05.
Oil bath temperature.
[b]
[c]
In the present work, we report a novel Lewis acid cat-
alytic system, the antimony(V) chloride-benzyltriethyl-
Isolated yield.
Adv. Synth. Catal. 2004, 346, 599 602
DOI: 10.1002/adsc.200303233
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599

An-ping Huang et al.
COMMUNICATIONS
the catalytic Friedel Crafts process.[10] A series of paral-
The activity of recovered catalyst was also examined.
lel reactions showed that AlCl3/TEBA and SbCl5/TEBA It is found that its catalytic activity decreases gradually:
(1:1) were less effective (entries 1 3), while SbCl5/ the yield in the acylation of anisole decreased from 96 to
TEBA (2:1) was effective. Studies were also carried 68% after seven runs (Figure 3).
out by using 5 mol % of the 2:1 complex with different
Examples of the Friedel Crafts acylation reaction
reaction periods and temperatures (entries 4 7), and 4- with acetyl chloride catalyzed by the complex of SbCl5/
methoxyacetophenone was obtained in 96% yield when TEBA (2:1) are shown in Table 2. This catalyst is not
the reaction was carried out at 1208C for 20 minutes (en- a good choice for the acetylation of benzene and gives
try 7). One of themost importantfeatures ofthis catalyst merely 37% isolated yield (entry 1), but it is highly effec-
is that the complex can be recycled. After reuse for more tive for acylating anisole and other electron-rich deriva-
than seven times, the catalyst is still active (Figure 3). An tives, such as toluene, xylene, and mesitylene (entries 2
additional feature of the BnNEt3(SbCl5)2Cl catalyst is 11). The catalyst affords the corresponding aromatic ke-
that the complex is inert to water and oxygen and easy tones in high yield. Under the optimized reaction condi-
to handle in the atmosphere without changing the cata- tions, this method could be carried out by using other
lytic activity of antimony chloride.
different acylation agents (Table 3), the reactions were
The structure of BnNEt3SbCl6 was determined by an also extended to the use of a sulfonyl chloride (Table 4);
X-ray single-crystal analysis (Figure 1)[11]; the catalyst in comparison with acetyl chloride these reactions take a
BnNEt3(SbCl5)2Cl is a pale yellow powder. We have longer period of time, but the yields are satisfactory.
not confirmed its accurate structure due to the lack of
In summary, this paper reports that the BnNEt3
a suitable single crystal, but it is probably a stable com- (SbCl5)2Cl complex is an efficient catalyst for Friedel
1
plex as indicated by its elemental analysis, H NMR Crafts reactions with satisfactory yields. BnNEt3
spectra and its fixed melting point, as shown in Figure 2. (SbCl5)2Cl can be reused and its activity could be main-
tained; this indicates the potential usefulness of this class
of catalysts for future studies and their applications in
the fields of organic synthesis, industrial production,
and green chemistry.
Experimental Section
Synthesis of the BnNEt3(SbCl5)2Cl Complex
To a solution of benzyltriethylammonium chloride (2.28 g,
10 mmol) and dry dichloromethane (10 mL) was slowly added
antimony(V) chloride (9 g, 30 mmol) at 08C in a conical flask
under a nitrogen atmosphere. At the end of this exothermic re-
action, filtration gave a pure pale yellow powder, which was
washed with dry dichloromethane and diethyl ether (three
times), and dried under vacuum to give the desired complex;
yield: 6 g (72%); mp 206 2088C; 1H NMR (300 MHz,
DMSO-d6): d¼1.3 (t, 9H, J¼6.6 Hz), 3.15 (q, 6H, J¼
6.6 Hz), 4.47 (s, 1H), 7.52 (s, 5H); anal. calcd. for C13H22Cl11
NSb2 (825.82): C 18.91, H 2.69, N 1.70; found: C 18.84, H
2.82, N 1.62.
Figure 1. X-ray crystal structure of BnNEt3SbCl6.
Figure 2. Proposed structure of BnNEt3(SbCl5)2Cl.
Typical Procedure for the Acylation of Anisole
(Table 2, entry 7)
The SbCl5/TEBA (2:1) catalyst (0.15 mmol, 5 mol %) was add-
ed to a mixture of anisole (6 mmol) and acetyl chloride
(3 mmol) in nitromethane (2.5 mL). The mixture was stirred
for 20 minutes at 1208C (oil bath temperature). After cooling,
the mixture was extracted with petroleum ether (60 908C, 5ꢁ
10 mL), the complex catalyst remained in the nitromethane,
which could be reused in the next reaction directly or could
be recovered by removal of nitromethane under reduced pres-
sure. The yield of recovered catalyst is above 98%. The petro-
leum ether layer was washed with water and dried over MgSO4.
Figure 3. The relationship of catalytic recycle and reaction
yield for the acylation of anisole in boiling nitromethane.
600
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Adv. Synth. Catal. 2004, 346, 599 602

Efficient Catalyst for Friedel Crafts Acylation Reactions
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Table 2. SbCl5/TEBA-catalyzed acetylation reactions.[a]
Entry
ArH
Acylating agent[b]
Time [min]
Yield [%][c]
1
2
3
4
5
6
7
8
9
PhH
PhMe
o-Xylene
m-Xylene
p-Xylene
Mesitylene
PhOMe
AcCl
AcCl
AcCl
AcCl
AcCl
AcCl
AcCl
AcCl
AcCl
AcCl
AcCl
120
60
30
30
30
20
20
20
30
20
20
37
82d
90
88
89
89
96
95
67
91
92
PhOEt
Phenyl ether
1,3-Dimethoxybenzene
1,4-Dimethoxybenzene
10
11
[a]
All reactions were carried out in boiling nitromethane until complete conversion of the substrate (as checked by TLC).
[b]
[c]
[d]
ArH/RCOCl/catalyst¼2/1/0.05 except for entries 2 and 3 (3/1/0.1).
Isolated yield.
ortho/para¼1/4.
Table 3. SbCl5/TEBA-catalyzed acylation reactions.[a]
After removal of the solvent under reduced pressure, the crude
product was purified by column chromatograph (petroleum
ether/ethyl acetate, 8:1) on silica get to afford 4-methoxyace-
tophenone; yield: 96%; 1H NMR (300 MHz, CDCl3): d¼2.53
(s, 3H), 3.85 (s, 3H), 6.90 (d, 2H, J¼11 Hz), 7.91 (d, 2H, J¼
11 Hz); EIMS: m/z¼150 (Mþ), 135, 107, 77, 43.
Entry
ArH
Acylating agent[b]
Time
[min]
Yield
[%][c]
1
2
3
4
5
6
7
8
9
PhOEt
PhCOCl
PhCOCl
PhCOCl
ClCH2COCl
ClCH2COCl
o-ClC6H4COCl
o-ClC6H4COCl
m-O2NC6H4COCl
m-O2NC6H4COCl
m-O2NC6H4COCl
150
150
150
150
150
150
120
120
180
120
83
75
75
73
75
77
81
81
77
75
o-Xylene
p-Xylene
o-Xylene
p-Xylene
PhMe
p-Xylene
PhOEt
PhMe
Typical Procedure for Catalyst Recycling in the
Acylation of Anisole
When the reaction was complete, the reaction mixture was ex-
tracted with petroleum ether several times; the catalyst re-
mained in the nitromethane phase and was reused for the
next reaction directly. In each run, the procedure above was
followed for the reaction. The reused catalyst system gave
68% reaction yield after recycling seven times (Figure 3).
10
p-Xylene
[a]
All reactions were carried out in boiling nitromethane un-
til complete conversion of the substrate (as checked by
TLC).
[b]
[c]
ArH/RCOCl/catalyst¼2/1/0.05.
Isolated yield.
Acknowledgements
YL thanks the NNSFC (No. 20172024 and No. 20021001) and
the ™Hundred Scientist Program∫ from the Chinese Academy
of Sciences for the financial support of this work.
Table 4. SbCl5/TEBA-catalyzed tosylation reactions.[a]
Entry
ArH
Acylating agent[b]
Time
[min]
Yield
[%][c]
1
2
3
4
5
6
o-Xylene
m-Xylene
p-Xylene
PhOEt
PhMe
p-Xylene
TsCl
TsCl
TsCl
PhSO2Cl
PhSO2Cl
PhSO2Cl
60
60
60
150
120
180
81
86
75
80
78
76
References and Notes
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Promoted Reactions; Kluwer Academic Publisher, Dor-
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[a]
All reactions were carried out in boiling nitromethane un-
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TLC).
[b]
[c]
ArH/RCOCl/catalyst¼2/1/0.05.
Isolated yield.
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Adv. Synth. Catal. 2004, 346, 599 602
asc.wiley-vch.de
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
601

An-ping Huang et al.
COMMUNICATIONS
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9.230(1), b¼14.281(2), c¼15.958(2) ä; a¼908, b¼
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¼
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¬
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3
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602
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Adv. Synth. Catal. 2004, 346, 599 602