Highly efficient solvent-free acetylation of alcohols with acetic anhydride catalyzed by recyclable sulfonic acid catalyst (SBA-15-Ph-Pr-SO3H)- An environmentally benign method

Article abstract of DOI:10.1139/v2012-018

The catalytic activity of highly thermal stable, hydrophobic, and complete heterogeneous propylsulfonic acid functionalized nanostructured SBA-15 for excellent acetylation of alcohols and phenols with acetic anhydride at ambient temperature in solvent-free conditions was examined under environmentally benign reaction conditions. The salient features of this protocol are the absence of solvent, a green experimental procedure, and simple reusability of the catalyst (at least five reaction cycles).

Full text of DOI:10.1139/v2012-018

464
Highly efficient solvent-free acetylation of alcohols
with acetic anhydride catalyzed by recyclable
sulfonic acid catalyst (SBA-15–Ph–Pr–SO3H) — An
environmentally benign method
Daryoush Zareyee, Abdollah Razaghi Ghadikolaee, and Mohammad A. Khalilzadeh
Abstract: The catalytic activity of highly thermal stable, hydrophobic, and complete heterogeneous propylsulfonic acid
functionalized nanostructured SBA-15 for excellent acetylation of alcohols and phenols with acetic anhydride at ambient
temperature in solvent-free conditions was examined under environmentally benign reaction conditions. The salient features
of this protocol are the absence of solvent, a green experimental procedure, and simple reusability of the catalyst (at least
five reaction cycles).
Key words: solid sulfonic acid, SBA-15, heterogeneous catalyst, acetylation, solvent-free.
Résumé : Le SBA-15 est un produit nanostructuré à base d’acide propylsulfonique fonctionnalisé qui est très stable vis-à-
vis de la chaleur, hydrophobe et totalement hétérogène. On a étudié son activité catalytique comme excellent catalyseur pour
la réaction d’acétylation d’alcools et de phénols à l’aide d’anhydride acétique, à la température ambiante, dans des condi-
tions expérimentales sans solvant et écologiques. Ce protocole est principalement caractérisé par l’absence de solvant, par
son caractère écologique et la facilité de réutilisation du catalyseur (dans au moins cinq cycles réactionnels).
Mots‐clés : acide sulfonique solide, SBA-15, catalyseur hétérogène, acétylation, sans solvant.
[Traduit par la Rédaction]
Introduction
ditions, long reaction times, poor yields of the desired
products, and tedious workup procedures. Another disad-
vantage is that most of these catalysts need organic sol-
vents as media for acylation, thereby generating large
amounts of corrosive and toxic waste. On the other
hand, there are some toxicity and difficulties in separating
conventional homogeneous catalysts from products.
One of the most promising solutions to these problems
seems to be immobilization of catalysts or using ecofriendly
solvent-free reaction conditions. Heterogeneous catalysts give
generally higher selectivity and typically require easier work-
up procedures. Along this line, alumina-supported MoO3,20
NaHSO4·SiO2,21 polymer-supported Gd(OTf)3,22 cobalt(II)
salen complex,23 and sulfuric acid ([3-(3-silicapropyl)sul-
fanyl]propyl)ester24 were also reported as heterogeneous cata-
lysts for acylation of alcohols. Despite a number of
improvements, some of these procedures still suffer from
long reaction times,22,23 high temperatures,23 the use of toxic
organic solvents,21 and nonrecoverable catalysts,21 which re-
sult in the generation of a large amount of toxic waste. Thus,
introduction of inexpensive and green catalysts for this pur-
pose is still in much demand.
The use of protecting groups is highly significant in or-
ganic synthesis and is often the key to the success of many
synthetic enterprises. Among the various protecting groups
used for the hydroxyl function, acetyl is the most common
group in view of its facile introduction, being stable to the
acidic reaction conditions, and also being easily removable
by mild alkaline hydrolysis.1 The acetylation of alcohols and
phenols provides an efficient route for protecting –OH
groups during oxidation, peptide coupling, and glycosidation
reactions.2 The most common and cheap acetylating regent is
activated carboxylic acid derivative acetic anhydride3 in the
presence of amine bases like pyridine,4 4-diaminopyridine
(DMAP),5 triethylamine,3 and 4-pyrrolidinopyridine.4 Protic
acids are also known to catalyze the acetylation process.6 Ad-
ditionally, various Lewis acids including Sc(OTf)3,7 In(OTf)3,8
Ce(OTf)3,9 Gd(OTf)3,10 Al(OTf)3,11 Fe(ClO4)3,12 Mn(OAc)2,13
I2,14 La(NO3)36H2O,15 SnIV(TPP)(BF4)2,16 TiCl3(OTf),17
H14[NaP5W29MoO110],18 and borated zirconia19 have also
been investigated to meet the demand for more efficient
methods. However, some of the base catalysts are toxic
and possess offensive odours,3–5 and the other methods
have some serious drawbacks such as harsh reaction con-
Received 12 October 2011. Accepted 26 January 2012. Published at www.nrcresearchpress.com/cjc on 26 April 2012.
D. Zareyee, A.R. Ghadikolaee, and M.A. Khalilzadeh. Department of Chemistry, Qaemshahr Branch, Islamic Azad University,
Qaemshahr, Iran.
Corresponding author: Daryoush Zareyee (e-mail: zareyee@gmail.com; zareyee.d@qaemshahriau.ac.ir).
Can. J. Chem. 90: 464–468 (2012)
doi:10.1139/V2012-018
Published by NRC Research Press

Zareyee et al.
465
Scheme 1. Schematic representation for solvent-free acylation of al-
cohols with Ac2O using SBA-15–Ph–Pr–SO3H.
Experimental section
General acetylation procedure
In a round-bottom flask (10 mL) equipped with a magnetic
stirrer, SBA-15–Ph–Pr–SO3H (12 mg, 2 mol %) was added to
the substrate (1 mmol) and acetic anhydride (1.2 mmol), and
the mixture was stirred at room temperature for the period of
time indicated in Table 1. After completion of the reaction
(TLC), the reaction mixture was filtered and the catalyst was
rinsed with ethyl acetate and then was recovered. After the
organic layer was washed with saturated NaHCO3 and water,
the aqueous layer was extracted with ethyl acetate and dried
over anhydrous Na2SO4, filtered, and evaporated. The com-
bined organic layer was subjected to column chromatography
on silica gel to afford pure acetate. Characterization of some
1
products was achieved by H and 13C NMR.
Results and discussion
Recently, we have prepared and used heterogeneous and
hydrophobic sulfonic acid SBA-15–Ph–Pr–SO3H as an effi-
cient recoverable catalyst in some organic reactions.25,26
Therefore, as a part of our continuing interest in the develop-
ment and utility of this catalyst, having both acidic sites and
phenyl groups inside the mesochannel of SBA-15, herein, we
wish to report the applicability of SBA-15–Ph–Pr–SO3H as
an efficient, environmentally benign, and reusable catalyst in
the promotion of the acetylation of alcohols and phenols with
acetic anhydride. All reactions were performed in solvent-free
reactions at room temperature and under complete heteroge-
neous reaction conditions in excellent yields (Scheme 1 and
Table 1; also see the Supplementary data).
Initially, the effect of catalyst was investigated in the
model reaction of benzyl alcohol with acetic anhydride, and
several sets of reaction conditions were examined. Benzyl al-
cohol (1 mmol) was treated with acetic anhydride (1.2 mmol)
in the absence of catalyst. As can be seen in Table 1, the cor-
responding product was obtained in 30% GC yield after
10 min (Table 1, entry 1). To evaluate the quantity of SBA-
15–Ph–Pr–SO3H, 1, 2, and 3 mol % of catalyst was used in
the acetylation of benzyl alcohol for 10 min under solvent-
free reaction conditions. It was observed that this reaction
goes well in the presence of 2 mol % of catalyst (Table 1,
entry 1). Use of a higher amount of catalyst (3 mol %) nei-
ther improves the yield nor the reaction time. Further studies
have showed that all procedures work well with a 1:1.2 molar
ratio of substrate to Ac2O in the presence of 2 mol % of
SBA-15–Ph–Pr–SO3H without solvent at room temperature.
On the basis of these results, we investigated the scope of
the substrate alcohols and phenols with respect to the SBA-
15–Ph–Pr–SO3H catalyst-mediated acetylation, and the re-
sults obtained are summarized in Table 1.
were also transformed to the respective acetates (Table 1,
entries 6 and 7). Meanwhile, acetylation of primary and
secondary aliphatic alcohols was performed in excellent
yields in short reaction times (Table 1, entries 8–16). Phe-
nol (Table 1, entry 17) and its derivatives (Table 1, entries
18–23) were also subjected to acetylation satisfactorily. It
was also found that SBA-15–Ph–Pr–SO3H effectively cata-
lyzed the acetylation of diols and triols (Table 1, entries
24–26). Interestingly, adamantanol was also converted to
the corresponding acetate as a model for acetylation of the
hindered tertiary alcohols (Table 1, entry 27). The assigned
structures were established from their spectral properties (1H
and 13C NMR) and by comparison with available authentic
data.
To clarify the merit of the catalyst, we compared the re-
sults of acetylation reaction of alcohols with some heteroge-
neous catalysts.21–23 It can be concluded that the higher
conversion of starting materials, shorter reaction times, and
solvent-free reaction conditions for catalyst SBA-15–Ph–Pr–
SO3H might likely be attributed to the larger pore size of or-
dered SBA-15 and the beneficial influence of phenyl groups
in close proximity to the sulfonic acid groups. Based on these
observations, it is clear that the pore size and hydrophobic
character of the catalyst are crucial parameters in the effec-
tiveness of sulfonic acid based catalysts for the catalysis of
the acetylation reaction, especially in solvent-free reaction
conditions.
The general efficiency of this reaction is evident from the
fact that a variety of hydroxy compounds, including primary
(aromatic and aliphatic), secondary (acyclic, cyclic, and ben-
zylic), tertiary alcohols, and phenols, acetylated with acetic
anhydride in the presence of 0.02 mmol of catalyst at room
temperature were obtained in excellent yields during a short
reaction time (Table 1). Primary benzylic alcohols with electron-
releasing and electron-withdrawing groups were acylated,
and the corresponding acetates were obtained in excellent
yields (Table 1, entries 1–5). Secondary aromatic alcohols
Reuse of the catalyst is an important aspect of any indus-
trial process. Compared with traditional methods using vola-
tile toxic solvents and nonrecoverable catalysts, which are
energy consuming and environmentally malign, the ease of
recycling is an attractive property of catalyst SBA-15–Ph–
Pr–SO3H for environmental protection and economic reasons.
The catalyst could be stored and handled under open air con-
ditions. To test the recyclability of the catalyst, the reaction
was conducted with benzyl alcohol in the presence of catalyst
Published by NRC Research Press

466
Can. J. Chem. Vol. 90, 2012
Table 1. Solvent-free acetylation of alcohols catalyzed by SBA-15–Ph–Pr–SO3H at room temperature.
Time
Yield
Entry Substrate
1
(min) (%)a,b
Product
O
10
96 (30)c
OH
O
CH3
O
OH
O
CH3
2
20
25
100
95
Cl
Cl
Cl
Cl
O
OH
3
O
CH3
Cl
Cl
O
OH
OH
O
CH
3
4
35
92
O2N
O
N
2
O
O
CH
3
5
10
10
98
H3C
H C
3
CH3
OH
CH3
O
6
7
100
O
CH3
O
OH
O
CH3
30
91
O
OH
8
9
3
3
99
99
O
OH
O
O
10
10
5
100
100
O
OH
O
O
OH
11
12
O
OH
O
CH3
20
20
30
95
O
H3C
OH
H3C
O
CH3
13
97
O
OH
O
CH3
14
100
O
for 10 min, which gave a conversion of 96%. The catalyst
was quantitatively recovered by simple washing and filtration
methods and proved to be reusable up to five times without
any appreciable loss of catalytic activity. It is noteworthy
that the catalyst-free solution was then left for 10 h, but no
further reaction took place. This reusability demonstrates the
high stability and turnover of catalyst under the conditions
employed.
Published by NRC Research Press

Zareyee et al.
467
Table 1. (concluded).
Time
(min)
30
Yield
(%)a,b
100
Entry Substrate
15
Product
OH
O
CH3
O
H3C
H3C
O
OH
O
16
17
18
19
25
15
40
10
98
O
CH3
OH
100
91
O
O
CH3
OH
O
Cl
Cl
H3C
O
CH3
H3C
OH
100
O
CH3
CH3
O
CH3
OH
20
21
50
45
100
100
O
O2N
O2N
O
CH3
OH
O
O
NO2
NO2
OH
O
CH3
22
23
24
90
70
20
88
OH
O
CH3
100
98
O
O
H3C
O
CH3
CH3
HO
OH
OH
O
O
O
O
O
O
25
17
97
H3C
H3C
O
O
HO
HO
CH3
OH
O
O
H3C
O
26
27
20
25
95
98
OH
O
O
O
CH3
OH
aIsolated yields.
bReaction conditions: catalyst (0.02 mmol), alcohol (1 mmol), Ac2O (1.2 mmol), room temperature, solvent-free conditions.
cReaction performed in the absence of catalyst.
tive catalyst for solvent-free acetylation of alcohols at
ambient temperature. In the presence of this catalyst, an al-
most stoichiometric amount of AC2O is necessary. Moreover,
this catalyst offers mild reaction conditions with short reaction
Conclusions
In summary, we have introduced highly efficient, hydro-
phobic, and reusable catalyst SBA-15–Ph–Pr–SO3H as an ac-
Published by NRC Research Press

468
Can. J. Chem. Vol. 90, 2012
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in the laboratory and stored for an extended period of time.
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Supplementary data
Supplementary data are available with the article through
the journal Web site at http://nrcresearchpress.com/doi/suppl/
10.1139/v2012-018.
Acknowledgements
The authors acknowledge the Islamic Azad University of
Qaemshahr Research Councils for support of this work.
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