Friedel-crafts acetylation, propionylation, and butyrylation of toluene catalyzed by solid superacids

Article abstract of DOI:10.1246/bcsj.76.1071

The liquid-solid phase acetylation of toluene with acetic anhydride was carried out over solid superacids of sulfated metal oxides (SO₄/MeO_x) and supported metal oxides (Me¹O_x/Me²O_y) selected from the results in the benzoylation of toluene with benzoic anhydride [K. Arata, H. Nakamura, and M. Shouji, Appl. Catal. A: General, 197, 213 (2000)]. The reaction was conducted by adding dropwise a mixture of 2 mmol of acetic anhydride and 2 mL of toluene onto 0.5 g of catalyst suspended in 13 mL of toluene with stirring at 110 °C in the first period of 30 min, followed by stirring the mixture for 2 h. The yields of 2′-, 3′-, and 4′-methylacetophenones in the distribution of 9-10% 2′-, 1-2% 3′and 89-90% 4′-isomers were 24 and 13% for the sulfated metal oxides of SO₄/ZrO₂ and SO₄/SNO₂, those by Pt and Ru promoted sulfated zirconias (Pt-, Ru-SO₄/ZrO₂) being 21 and 28%, respectively. The supported metal oxides of Fe₂O₃/ ZrO₂ and WO₃/ZrO₂ gave yields of 18 and 15%, respectively. The propionylation and butyrylation of toluene with propionic and butyric anhydrides were performed over SO₄/ZrO₂, SO₄/SnO₂, Pt-SO₄/ZrO₂, and Ru-SO₄/ZrO₂; the yields of 7-9% o- and 91-93% p-isomers were 31, 26, 32, and 44% for propionylation and 46, 29, 44, and 55% for butyrylation, respectively. The SO₄/ZrO₂ catalyst gave a 100% yield of 4′-methoxyacetophenone for the acetylation of anisole with acetic anhydride.

Full text of DOI:10.1246/bcsj.76.1071

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1071–1074 (2003) 1071
Friedel–Crafts Acetylation, Propionylation, and Butyrylation of Toluene
Catalyzed by Solid Superacids
ꢀ
ꢀ
Hideo Nakamura, Yuki Kashiwara, and Kazushi Arata
Department of Science, Hokkaido University of Education, Hachiman-cho, Hakodate 040-8567
(Received September 30, 2002)
The liquid–solid phase acetylation of toluene with acetic anhydride was carried out over solid superacids of sul-
fated metal oxides (SO4/MeOx) and supported metal oxides (Me1Ox/Me2Oy) selected from the results in the benzoyla-
tion of toluene with benzoic anhydride [K. Arata, H. Nakamura, and M. Shouji, Appl. Catal. A: General, 197, 213
(2000)]. The reaction was conducted by adding dropwise a mixture of 2 mmol of acetic anhydride and 2 mL of toluene
ꢁ
onto 0.5 g of catalyst suspended in 13 mL of toluene with stirring at 110 C in the first period of 30 min, followed by
stirring the mixture for 2 h. The yields of 20-, 30-, and 40-methylacetophenones in the distribution of 9–10% 20-, 1–2% 30-
and 89–90% 40-isomers were 24 and 13% for the sulfated metal oxides of SO4/ZrO2 and SO4/SnO2, those by Pt and Ru
promoted sulfated zirconias (Pt-, Ru-SO4/ZrO2) being 21 and 28%, respectively. The supported metal oxides of Fe2O3/
ZrO2 and WO3/ZrO2 gave yields of 18 and 15%, respectively. The propionylation and butyrylation of toluene with pro-
pionic and butyric anhydrides were performed over SO4/ZrO2, SO4/SnO2, Pt-SO4/ZrO2, and Ru-SO4/ZrO2; the yields of
7–9% o- and 91–93% p-isomers were 31, 26, 32, and 44% for propionylation and 46, 29, 44, and 55% for butyrylation,
respectively. The SO4/ZrO2 catalyst gave a 100% yield of 40-methoxyacetophenone for the acetylation of anisole with
acetic anhydride.
The catalytic acylation of aromatics via the Friedel–Crafts
reaction remains a prerequisite challenge to green technology.
Traditional methods depend on the use of at least stoichio-
metric quantities of Lewis acids, such as aluminium trichloride
and boron trifluoride, because the Lewis catalysts are con-
sumed by coordination with the formed aromatic ketones.1;2
A large amount of the acids and their waste matter after
work-up procedures cause serious environmental problems;
the use of toxic Friedel–Crafts catalysts involves many pro-
blems to be solved. As a goal, there have been several efforts
to conduct the reaction using catalytic amounts of acidic
promoters.3{8 Recently, Kobayashi and co-workers found rare
earth metal trifluoromethanesulfonates, RE(OTf)3, to be effi-
cient catalysts for acylation;9 a catalytic amount of the materi-
als was easily recovered and reused. Yadav and Pujari synthe-
sized 40-chlorobenzophenone, a pharmaceutical intermediate,
via the acylation of benzene with 4-chlorobenzoyl chloride
over sulfated zirconia (SO4/ZrO2) as a catalyst,10 though the
acid in place of the acid chloride as the acylating agent was
better for a genuinely environmental trend.
Solid superacids of sulfated metal oxides (SO4/MeOx) and
supported metal oxides (Me1Ox/Me2Oy) were synthesized by
the addition of sulfate species to oxide surfaces of Fe, Ti,
Zr, Hf, Sn, Al, and Si, or by supporting SnO2, TiO2, Fe2O3,
and ZrO2 with WO3 and ZrO2 with MoO3 and B2O3,11;12 me-
tal-promoted superacids, which are also being prepared.13{15
A previous paper reported on a comparative study of those
superacids for the benzoylation of toluene with benzoic anhy-
dride and benzoyl chloride in the liquid–solid phase.16 A re-
lationship was obtained between the highest acid strength of
the catalysts and the acylated yields. Most of the superacids
gave satisfactory yields of 20-, 30-, and 40-methylbenzophe-
nones with the acid anhydride as the acylating agent. In con-
sideration of the results, several catalysts were also examined
in a less reactive acylation: the acetylation of toluene with ace-
tic anhydride or acetyl chloride. However, satisfactory results
were not obtained.
Chiche and others reported on the acylation of toluene and
p-xylene by various carboxylic acids catalyzed by a Y-fauja-
site-type zeolite exchanged with the Ce3þ cation.17 In a plot
of the yield as a function of the number of carbon atoms of car-
boxylic acids, the yield increased linearly as the hydrocarbon
chain was lengthened. This phenomenon is not encountered
in classical Friedel–Crafts reactions, and shows acetylation
to be the most difficult acylation, because of a difficulty in
the formation of an intermediate acetyl cation (MeCOþ) from
alkyl chain acid anhydrides and halides. Thus, liquid–solid
acetylation is an attractive challenge for clean technology as
well as for organic synthesis; the present paper is concerned
with a systematic study of several superacids for the acetyla-
tion of toluene with acetic anhydride, together with acylations
with longer hydrocarbon chains, propionylation and butyryla-
tion at mild temperatures below reflux operating in a batch
mode. To the best of our knowledge, the heterogeneous ace-
tylation of toluene using solid acidic promoters has not been
reported in detail.
Experimental
Catalysts. Preparation of Zirconium(d) and Tin(d) Hy-
droxides: 1. Zr(OH)4. The hydroxide was obtained by hydro-
lyzing ZrOCl2 with aqueous ammonia to pH 8 at a temperature of
60–70 ꢁC; the precipitates were washed several times with hot
water, and finally dried.
2. Sn(OH)4. Aqueous ammonia was added into a solution of

1072 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Heterogeneous Acylation of Aromatics
ꢁ
SnCl4 in water with stirring at 60 C, the final pH of the solution
being 8. The precipitates were washed by decantation five times
using hot water, and dried.
their spectral data and retention times in GLC with those of
authentic samples. Since toluene was in excess, the yields were
based on the acylating reagents.
Identification and Isolation of the Product. 1H NMR spectra
were recorded on a JEOL JNM-EX270 spectrometer. Silica-gel
column chromatography was performed using Merck Kiesel 60
(70–230 mesh).
ꢁ
The precipitated hydrogels were dried at 100 C for 24 h and
powdered to below 100 mesh.
Sulfate Treatment of Metal Hydroxides: Materials prepared
as described above were treated with sulfate ions by exposing 2 g
of the hydroxide in 30 mL of aqueous sulfuric acid on a glass filter
for 1 h, followed by filtering, drying them at room temperature,
and finally calcining. The concentration of H2SO4 was 0.5 and
3 M (1 M = 1 mol dmꢂ3) for the hydroxides of Zr and Sn, respec-
tively; the calcination temperature was 550 ꢁC for Sn and 600 ꢁC
for Zr. The prepared catalysts are indicated as SO4/ZrO2 and SO4/
SnO2.
20-Methylpropiophenone. 1H NMR (CDCl3) ꢀ 7.63–7.64 (m,
1H), 7.31–7.36 (m, 1H), 7.16–7.27 (m, 2H), 2.92 (q, J ¼ 7:3 Hz,
2H), 2.49 (s, 3H), 1.19 (t, J ¼ 7:3 Hz, 3H).
40-Methylpropiophenone.
1H NMR (CDCl3) ꢀ 7.85 (d,
J ¼ 8:25 Hz, 2H), 7.24 (d, J ¼ 8:25 Hz, 2H), 2.88 (q, J ¼ 7:3
Hz, 2H), 2.31 (s, 3H), 1.13 (t, J ¼ 7:3 Hz, 3H).
20-Methylbutyrophenone.
1H NMR (CDCl3) ꢀ 7.60 (d,
Two more SO4/ZrO2 catalysts were prepared. One was pre-
pared by calcining sulfated zirconia of Wako Pure Chemical In-
dustries, Ltd., at 550 C. The other was prepared by powdering
zirconium hydroxide, XZO 632/03, of MEL Chemicals (dried at
100 ꢁC for 24 h), followed by treating with 0.5 M H2SO4 and cal-
cining at 600 ꢁC. The former catalyst was denoted as SO4/ZrO2-1
and the latter as SO4/ZrO2-2; thus, the sulfated zirconia prepared
from ZrOCl2 was denoted as SO4/ZrO2-3.
J ¼ 7:26 Hz, 1H), 7.16–7.39 (m,3H), 2.87 (t, J ¼ 7:26 Hz, 2H),
2.48 (s, 3H), 1.74 (hex, J ¼ 7:26 Hz, 2H), 0.99 (t, J ¼ 7:26 Hz,
3H).
ꢁ
40-Methylbutyrophenone.
1H NMR (CDCl3) ꢀ 7.86 (d,
J ¼ 8:25 Hz, 2H), 7.25 (d, J ¼ 8:25 Hz, 2H), 2.92 (t, J ¼ 7:26
Hz, 2H), 2.41 (s, 3H), 1.76 (hex, J ¼ 7:26 Hz, 2H), 1.00 (t,
J ¼ 7:26 Hz, 3H).
40-Methoxyacetophenone.
1H NMR (CDCl3) ꢀ 7.93 (d,
Preparations of Pt- and Ru-Added Sulfated Zirconias: Pt-
SO4/ZrO2-1, -2, and -3 were obtained by treating the correspond-
ing zirconium hydroxides with 0.5 M H2SO4, followed by drying,
J ¼ 8:9 Hz, 2H), 6.92 (d, J ¼ 8:9 Hz, 2H), 3.86 (s, 3H), 2.55
(s, 3H).
impregnating with aqueous H2PtCl6 6H2O (to obtain 3 wt% Pt in
ꢃ
Results and Discussion
the final catalyst after calcination), evaporating residual water,
ꢁ
Among solid superacids of sulfated and supported metal
oxides, SO4/ZrO2-1 showed the highest activity for the ben-
zoylation of toluene with benzoic anhydride,16 and thus acety-
lation was carried out under common solid–liquid conditions
with a mixture of 15 mL of toluene, 2 mmol of acetic anhy-
drying, and calcining in air at 600 C.
Ru-SO4/ZrO2-2 was obtained by impregnating Zr(OH)4 (XZO
632/03) with an aqueous solution of RuCl3 nH2O, followed by
ꢃ
evaporating residual water, drying at 300 ꢁC for 3 h, treating with
0.5 M H2SO4, drying, and finally calcining at 550 ꢁC, the concen-
tration being 3 wt% Ru, based on the hydroxide.
ꢁ
dride, and 0.5 g of the catalyst with stirring at 110 C for 4
h, though the yield was quite low, 8% (Entry 1 in Table 1).
Supplementary examinations were tried several times, but
the results were identical with the above. Most of the reactions
did not show a continual increase of yield with time, and the
catalyst failed to react further after 30–60 min. A question
arises concerning the deactivation of the catalyst, or the de-
composition of the anhydride, during the early stage of the
reaction. Thus, the reaction conditions were changed; the re-
sults are summarized in Table 1.
A catalyst suspended in 10 mL of toluene was added drop-
wise with stirring into a mixture of 5 mL of toluene and the
anhydride (2 mmol) in the first period of 5 or 20 min, followed
by continual stirring; even if the period was extended, the
yields hardly increased (Entry 2, 3). The anhydride mixed
with 2 mL of toluene was added dropwise into a mixture of tol-
uene (13 mL) and the catalyst for periods of 12 and 30 min,
and the yields were also promoted (Entry 4, 5); in particular,
the enhancement by a longer period of 30 min was three times,
24%. A long time of the dropping was tried; that is, a mixture
of 10 mL of toluene and the anhydride was added into the re-
maining toluene (5 mL)–catalyst solution during a period of 60
min, though the result was not the expected observation
(Entry 6).
All of the catalysts were calcined in Pyrex glass tubes in air for
3 h and sealed in ampoules while hot to avoid humidity until use.
Preparation of Superacids by Metal Oxides: WO3/ZrO2-2
was obtained by impregnating Zr(OH)4 (XZO 632/03) with aque-
ous ammonium metatungstate [(NH4)6(H2W12O40)], followed by
evapꢁorating water at room temperature, drying, and calcining at
800 C for 3 h. The concentration was 15 wt% W metal based
on the hydroxides. Fe2O3/ZrO2-2 was obtained by impregnating
Zr(OH)4 (XZO 632/03) with an aqueous solution of Fe(NO3)3,
followed by evaporating residual water, drying at 300 ꢁC for 3
h, treating with 0.5 M H2SO4, drying, and calcining at 700 ꢁC
for 26 h (2 wt% Fe).
The calcination at temperatures above 700 ꢁC was performed in
a ceramic crucible, followed by calcining in Pyrex glass tubes at
ꢁ
500 C for 1 h and sealing in ampoules until use.
Reaction Procedure. The acetylation was carried out with a
mixture of 15 mL (141 mmol) of toluene (purified by distillation
before use), 2 mmol of acetic anhydride (0.204 g), 0.5 g of cata-
lyst, and 0.185 g (1ꢁmmol) of tridecane as an internal standard
with stirring at 110 C under an argon atmosphere; a mixture of
0.204 g of the acid and 2 mL of toluene was added dropwise with
stirring onto catalyst suspended in 13 mL of toluene in the first
period of 30 min, followed by stirring the mixture for 2–3 h. A
small amount of the sample was withdrawn periodically with a
1 mL syringe, diluted with ethyl acetate, separated from the cata-
lyst by filtration, and analyzed by gas–liquid chromatography with
a FID detector using a 25 m column of OV-1701 BONDED in the
temperature range from 80 to 220 ꢁC at the programmed rate of 5
ꢁC/min. The product isomers were identified by a comparison of
In consideration of the above results, it is proposed that
CH3COOH derived from acetylation has an effect on the sub-
sequent reaction. Following the procedure of Entry 5, the re-
action was performed with the anhydride (2 mmol) mixed with
acetic acid (1.7 mmol) or with CH3COOH (2 mmol), without

H. Nakamura et al.
Bull. Chem. Soc. Jpn., 76, No. 5 (2003) 1073
Table 1. Acetylation of Toluene with Acetic Anhydride Catalyzed by SO4/ZrO2-1 at 110 ꢁC under
Various Conditions
Entry
Time/h
Yield/%
Condition
1
2
3
4
5
6
7
8
9
10
11
12
13
4
3
3
3
3
3
2
2
3
3
4
4
4
8
16
10
14
24
9
Stirring of toluene–Ac2O–catalyst
Dropping of catalyst–toluene into toluene–Ac2O for 5 min
Dropping of catalyst–toluene into toluene–Ac2O for 20 min
Addition of Ac2O–toluene into toluene–catalyst for 12 min
Addition of Ac2O–toluene into toluene–catalyst for 30 min
Addition of Ac2O–toluene into toluene–catalyst for 60 min
Addition of Ac2O–AcOH–toluene following Entry 5
Addition of AcOH–toluene following Entry 5
Stirring of toluene–Ac2O–catalyst–molecular sieves
Stirring of toluene–Ac2O–catalyst–silica gel
Addition of Ac2O–toluene into nitrobenzene–catalyst
Addition of Ac2O–toluene into chlorobenzene–catalyst
Addition of AcOEt–toluene following Entry 5
1
Trace
0.3
0.4
1
2
0
the anhydride, as the acylating agent; the expected results were
observed (Entry 7, 8). The inactivity with the acid is based on
its coordination with an acid site on the catalyst surface as a
result of lowering the acidity for acetylation. Thus, the effect
of the adsorbent for produced CH3COOH was examined; acet-
ylation was carried out with stirring the mixture along with 2 g
of dried molecular sieve 4A or silica gel, but no reaction pro-
gressed (Entry 9, 10). The anhydride was probably adsorbed
on the adsorbents.
In the homogeneous Friedel-Crafts reaction, the reaction is
frequently performed using solvents, such as nitromethane
and acetonitrile.1;2 In order to raise the yield, acetylation
was tried in nitrobenzene or chlorobenzene as a solvent fol-
lowing the procedure of Entry 5: the addition of Ac2O (2
mmol)–toluene (2 mL) into a mixture of solvent (13 mL)
and catalyst, though the results were not satisfactory (Entry
11, 12) because of a probable coordination of unpaired elec-
trons of nitrobenzene or chlorobenzene with the catalyst sur-
face for lowering the acidity. Finally, the acetylation with
ethyl acetate as the acylating reagent, without producing
CH3COOH during the reaction, was examined as a result of
the ineffectiveness (Entry 13) of acylations using esters as
the acylating agent, usually being difficult.18
Table 2. Acetylation of Toluene with Acetic Anhydride
ꢁ
over Various Solid Catalysts at 110 C for 2 h
Isomers/%
Catalyst
Yield/%
o-
m-
p-
SO4/ZrO2-1
SO4/ZrO2-2
SO4/ZrO2-3
SO4/SnO2
Pt-SO4/ZrO2-1
Pt-SO4/ZrO2-2
Pt-SO4/ZrO2-3
Ru-SO4/ZrO2-2
Fe2O3/ZrO2-2
WO3/ZrO2-2
24
22
22
13
14
19
21
28
18
15
11
9
9
9
9
9
9
9
10
8
1
1
1
2
2
1
2
2
1
1
88
90
90
89
89
90
89
89
89
91
Table 3. Acylation of Toluene with Propionic and Butyric
ꢁ
Anhydrides at 110 C for 2 h
Propionylation
Isomers/%
Butyrylation
Catalyst
Isomers/%
Yield/%
Yield/%
o-
p-
o-
p-
Since the procedure of Entry 5 gave the highest yield, the
acetylation following the method was performed over other
sulfated zirconias, and their Pt or Ru promoted materials along
with SO4/SnO2, Fe2O3/ZrO2, and WO3/ZrO2, whose catalysts
were highly effective for the benzoylation of toluene with ben-
zoic anhydride; the results are given in Table 2. Although
yields higher than 24%, obtained by SO4/ZrO2-1, were ex-
pected, only Ru-SO4/ZrO2-2 showed a expected value of
28%. In benzoylation, the preparation method of the catalyst
largely controlled the catalytic activity, particularly for the
SO4/ZrO2 matter, though the present acylation did not show
any difference in the yields. Although a modification of
SO4/ZrO2 by the addition of Pt and Ru also led to a large pro-
motion of activity for benzoylation, the present results were
not better than expected.
SO4/ZrO2-1
SO4/SnO2
Pt-SO4/ZrO2-2
Ru-SO4/ZrO2-2
31
26
32
44
8
7
7
7
92
93
93
93
46
29
44
55
9
7
8
8
91
93
92
92
tion is similar to that by the usual homogeneous reaction.
As described in the introduction, acetylation is the most dif-
ficult acylation because of the formation of its intermediate
(MeCOþ). Therefore, more reactive acylations by acylating
reagents with longer hydrocarbon chains, propionylation and
butyrylation, were performed with several catalysts (Table
2); SO4/ZrO2-1, SO4/SnO2, Pt-SO4/ZrO2-2, and Ru-SO4/
ZrO2-2 were examined in reactions of toluene with propionic
and butyric anhydrides under the same conditons as the acety-
lation of Entry 5 in Table 1 (the results in Table 3). All of the
catalysts gave yields higher than those of acetylation for pro-
The products were 20-, 30-, and 40-methylacetophenones,
and the distribution was not much varied: 9–10% 20-, 1–2%
30-, and 89–90% 40-isomers. The predominant para-substitu-

1074 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Table 4. Acetylation of Anisole
Heterogeneous Acylation of Aromatics
Entry
1
Time/h
Yield/%
Condition
1
2
1
78
90
100
Entry 5 in Table 1
2
Entry 1 in Table 1
References
pionylation as well as butyrylation; the latter was higher than
the former in each case. The Ru-SO4/ZrO2-2 catalyst again
showed the highest yields in both acylations, as was observed
with acetylation. The reactivity with acylating reagents is
(PrCO)2O > (EtCO)2O > (MeCO)2O, which agrees with their
intermediate stability of PrCOþ > EtCOþ > MeCOþ.
The product distribution was not varied, 7–9% o- and 91–
93% p-isomers for the both reactions, 40-methylpropiophenone
and 40-methylbutyrophenone, and their meta-isomers were not
analyzed because of minor yields.
The present catalyst was examined in a more reactive acet-
ylation, the acetylation of anisole with acetic anhydride;
Table 4 gives the results for catalysis by SO4/ZrO2-1. It can
be seen how effective the present catalyst is for anisole, in
comparison with toluene. In this case, a quantitative yield
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suspended mixture. The product was 40-methoxyacetophe-
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was 100% active in yield and selective towards p-methoxyace-
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