Solvent-free acetylation and tetrahydropyranylation of alcohols catalyzed by recyclable sulfonated ordered nanostructured carbon

Article abstract of DOI:10.2478/s11696-013-0369-x

Rapid and practical green acetylation and tetrahydropyranylation routes of structurally diverse alcohols and phenols were applied under solvent-free reaction conditions providing excellent yields, using catalytic amounts of environmentally friendly sulfonated ordered nanoporous carbon (CMK-5-SO ₃H). Non-toxic nature of the catalyst, its easy handling, recovery and reusability, and the absence of any solvent characterize the presented procedures as efficient methods. These procedures provide methods for the separation of the product by simple filtration.

Full text of DOI:10.2478/s11696-013-0369-x

Chemical Papers 67 (7) 713–721 (2013)
DOI: 10.2478/s11696-013-0369-x
ORIGINAL PAPER
Solvent-free acetylation and tetrahydropyranylation of alcohols
catalyzed by recyclable sulfonated ordered nanostructured carbon
Daryoush Zareyee*, Parastoo Alizadeh, Mohammad S. Ghandali,
Mohammad A. Khalilzadeh
Department of Chemistry, Qaemshahr Branch, Islamic Azad University, Qaemshahr, P.O. Box 163, Iran
Received 6 October 2012; Revised 16 January 2013; Accepted 22 January 2013
Rapid and practical green acetylation and tetrahydropyranylation routes of structurally diverse
alcohols and phenols were applied under solvent-free reaction conditions providing excellent yields,
using catalytic amounts of environmentally friendly sulfonated ordered nanoporous carbon (CMK-
5-SO3H). Non-toxic nature of the catalyst, its easy handling, recovery and reusability, and the
absence of any solvent characterize the presented procedures as efficient methods. These procedures
provide methods for the separation of the product by simple filtration.
c
ꢀ 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: sulfonated ordered nanoporous carbon, CMK-5-SO3H, acetylation, tetrahydropyrany-
lation, solvent-free
Introduction
1,4-benzoquinone (DDQ) (Tanemura et al., 1992),
ZnCl2 (Ranu & Saha, 1994), I2 (Deka & Sarma,
2001), tetrabutylammonium tribromide (Naik et al.,
2001), In(OTf)3 (Mineno, 2002), Li(OTf)3 (Karimi
& Maleki, 2002), polyaniline salts (Palaniappan et
al., 2002), Sc(OTf)3 (Karimi & Ma’mani, 2003),
Bi(OTf)3 ·4H2O (Stephens et al., 2003), PdCl2
(CH3CN)2 (Wang et al., 2004), imidazolium-based
tetrachloroindate(III) (Kim & Varma, 2005), copper
methanesulfonate-acetic acid (Wang et al., 2007b),
Fe(HSO4)3 (Shirini et al., 2007), and Al(OTf)3
(Williams et al., 2010). Although these methods are
satisfactory for many molecules, some of them have
serious limitations, e.g. harsh reaction conditions, ele-
vated reaction temperatures, long reaction times, high
catalyst to substrate ratio, organic solvents as media,
and tedious and time-consuming work-up procedure
which need be replaced by greener methods.
Acetyl and tetrahydropyranyl (THP) are the most
versatile protecting groups that are often used for the
protection of alcohol moieties due to their low cost,
easy installation, remarkable stability, and compati-
bility under various reaction conditions and reagents
(Greene & Wuts, 1991). Acetylation of alcohols pro-
vides an efficient route for protecting of –OH groups
during oxidation, peptide coupling, and glycosida-
tion reactions (Hanson, 1999); THP groups are also
the protecting group of choice in peptides (Bodan-
szky & Ondetti, 1966), nucleotides (van Boom et al.,
1971), carbohydrates (Augé et al., 1980), and steroids
(Djerassi, 1963). Many catalysts have already been
proposed for the acetylation of alcohols such as NbCl5
(Yadav et al., 2005), AlPW12O40 (Firouzabadi et
al., 2003), Sc(OTf)3 (Ishihara et al., 1996), In(OTf)3
(Chauhan et al., 1999), Al(OTf)3 (Kamal et al., 2007),
I2 (Phukan, 2004), 12-tungstophosphoric acid (Satam
& Jayaram, 2008), and H14[NaP5W29MoO110] (Ro-
manelli et al., 2010), and also for the tetrahydropy-
ranylation of alcohols including p-toluenesulfonic acid
(PTSA) (Corey et al., 1987), 2,3-dichloro-5,6-dicyano-
In recent years, solid acids catalysis has gained
much attention due to the advantages of hetero-
geneous catalysts, like simplified product isolation,
high selectivity, easy recovery of catalysts and re-
duced generation of harmful wastes (Corma, 1995).
Therefore, to address the improvement of environ-
*Corresponding author, e-mail: zareyee@gmail.com

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D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
Fig. 1. Schematic preparation of sulfonated ordered mesoporous carbon (CMK-5-SO3H) (catalyst 1).
mental safety in the production of chemicals un-
der milder reaction conditions, various solid catalysts
such as NaHSO4 ·SiO2 (Das & Thirupathi, 2007),
polymer supported Gd(OTf)3 (Yoon et al., 2008),
cobalt(II) salen complex (Rajabi, 2009), and sulfuric
acid ([3-(3-silicapropyl)sulfanyl]propyl)ester (Niknam
& Saberi, 2009) were reported for the acetylation,
and nafion-H (Olah et al., 1983), montmorillonite
(Hoyer et al., 1986), clays (Campelo et al., 1994), am-
berlyst (Bongini et al., 1979), H-Y zeolite (Kumar
et al., 1993), Al2(SO4)3 on silica gel (Nishiguchi &
Kawamine, 1990), silica chloride (Ravindranath et al.,
2001), sulfuric acid on silica gel (Heravi et al., 1999),
SO3H-functionalized amorphous silica (Shimizu et al.,
2004), sulfated zirconia (Reddy et al., 2005), and car-
bon supported sulfuric acid (Yang et al., 2008) for the
tetrahydropyranylation of hydroxyl group. Despite a
number of improvements, some of these procedures
still suffer from long reaction time, the use of volatile
and toxic organic solvents, and non-recoverable cata-
lysts which result in the generation of large amounts
of toxic waste. Thus, there is still a need for mild and
efficient alternative methods, especially using recov-
erable heterogeneous solid acids as catalysts for the
acetylation and tetrahydropyranylation of alcohols.
On the other hand, ordered nanoporous carbona-
ceous solid acids can also maintain strong acidity par-
ticipating thus in many industrially important acid-
catalyzed reactions. The carbon surface has been ex-
clusively used as a support substrate, especially as
electrodes with a wide potential window in electro-
chemistry for catalytic, analytical, and biotechnolog-
ical applications (Rice et al., 1990). Recently, Joo et
al. (2001) have synthesized ordered mesoporous car-
bon with periodic arrays of nanopores (CMK-5) us-
ing partially furfuryl alcohol-filled pores of Al-SBA-
15 as a hard template. In principle, mesoporous SBA-
15 with hexagonal array of nanotubes with microcon-
nections between the mesopores was produced by the
cooperative assembly process between silica species
(tetraethoxysilane, TEOS) and the amphiphilic tri-
block copolymer P123 in an aqueous medium (Yu et
al., 2002). Al-SBA-15 was obtained by the well disper-
sion of calcined SBA-15 into an aqueous solution of
AlCl3. Impregnation of furfuryl alcohol into Al-SBA-
15 by incipient wetness infiltration, polymerization of
furfuryl alcohol by Al (surface templating), heating of
the composite at 850◦C under vacuum, and removal
of the silica template by HF resulted in the synthe-
sis of ordered mesoporous carbon CMK-5. This ma-
terial shows high surface area, narrow pore size dis-
tribution, and large pore volume. Covalent attach-
ment of aryl sulfonic acid on ordered nanoporous car-
bon with mesoporosity both inside and between the
nanopipes can be performed by homogenous reduction
of 4-benzene-diazoniumsulfonate using hypophospho-
rous acid (Wang et al., 2007a) and it resulted in the
preparation of sulfonated ordered mesoporous carbon
(CMK-5-SO3H).
Therefore, in view of the emerging importance of
green chemistry and extending the use of recover-
able heterogeneous solid acids (Karimi & Zareyee,
2008, 2009; Zareyee et al., 2011, 2012), the applica-
tion of CMK-5-SO3H (catalyst 1) as a highly effective
and reusable catalyst in both acetylation and tetrahy-
dropyranylation of alcohols and phenols under solvent-
free reaction conditions at ambient temperature is in-
troduced herein (Fig. 1) (See supporting material for
experimental details).
Experimental
Acetylation procedure: CMK-5-SO3H (13 mg, 2
mole %) was added to the mixture of alcohol (1 mmol)
and acetic anhydride (Ac2O) (1.2–1.5 mmol), and the
reaction mixture was stirred in a round bottom flask at
room temperature for the appropriate time (Table 1).
After the completion of the reaction (TLC), the re-

D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
715
Table 1. CMK-5-SO3H (2 mole %) catalyzed acetylation of alcohols and phenols at room temperature and under solvent-free
conditions
Ac2O
mmol
Time
min
Yielda
%
Entry
1
Substrate
Product
1.2
1.5
20
10
94
100
2
1.2
5
99
3
4
5
1.2
1.2
1.2
5
5
98
99
99
20
6
7
8
1.5
1.5
1.5
10
10
10
97
98
97
9
1.5
1.5
10
10
99
96
10
11
12
1.5
1.5
15
10
90
94
13
1.5
10
98
14
15
1.5
1.5
10
10
90
94

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D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
Table 1. (continued)
Ac2O
Time
min
Yielda
%
Entry
16
Substrate
Product
mmol
1.2
10
99
1.2
1.5
15
2
99
96
17
18
19
1.5
1.2
5
99
99
25
20
21
1.5
30
90
1.2
1.5
20
10
84
99
22
23
1.2
1.2
15
5
99
99
1.2
1.5
10
15
45
99
24
25
2.5
3.6
10
15
97
95
26
a) Estimated by GC.
action mixture was filtered and diluted with water.
It was extracted with ethyl acetate (3 × 10 mL) and
the combined organic phases were dried (Na2SO4), fil-
tered, and evaporated under reduced pressure. Com-
pounds with the purity below 95 % were further puri-
fied using column chromatography on silica gel to af-
ford pure acetate. Characterization of some products
%) was added and stirring continued at ambient tem-
perature for the period of time indicated in Table 2.
Progress of the reaction was monitored by GC and
TLC (eluent, hexane : ethyl acetate volume ratio, ϕr
= 4 : 1). When the reaction was completed, 15 mL of
ethyl acetate were added and the mixture was filtered.
The solid was washed with ethyl acetate. The organic
phase was evaporated under reduced pressure to give
the products in good to excellent yields (Table 2). If
needed, further purification was performed by passing
through a short column of silica gel.
1
was achieved by H NMR and 13C NMR.
Tetrahydropyranylation procedure: to a stirred
mixture of alcohol (1 mmol) and 3,4-dihydropyran
(DHP) (0.129 g, 1.5 mmol), catalyst 1 (13 mg, 2 mole

D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
717
Table 2. CMK-5-SO3H (2 mole %) catalyzed tetrahydropyranylation of alcohols and phenols at room temperature and under
solvent-free conditions
Time
min
Yielda
%
Entry
Substrate
Product
1
2
30
70
100
82
3
4
40
80
85
75
5
6
7
50
60
90
95
88
100
8
9
100
75
94
100
10
11
45
60
100
100
12
13
50
75
100
h 95
14
15
16
80
100
95
91
98
94
17
60
96

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D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
Table 2. (continued)
Time
min
Yielda
%
Entry
Substrate
Product
18
19
80
70
100
85
20
21
160
70
70
99
92
22
100
a) Estimated by GC.
Fig. 2. Acetylation and tetrahydropyranylation of benzyl alcohol using 2 mole % of CMK-5-SO3H at room temperature under
solvent-free conditions.
Results and discussion
Having established the optimal reaction condi-
tions, a study to explore the scope of this catalytic
system was initiated. First, acetylation of a variety of
primary aromatic and aliphatic alcohols with Ac2O
was examined (Table 1, entries 1–8). It is noteworthy
that the reactions proceeded efficiently in good to ex-
cellent yields for all studied alcohols. This method is
also efficient for the acetylation of secondary aliphatic
alcohols (Table 1, entries 9–15), and for phenol (Ta-
ble 1, entry 16) and its derivatives (Table 1, entries
17–22). 1-Naphthol and 2-naphthol also underwent the
reaction producing the corresponding esters in excel-
lent yields (Table 1, entries 23 and 24). It has also
been found that CMK-5-SO3H effectively catalyzed
the acetylation of diols and triols (Table 1, entries 25
and 26).
Our initial investigations were focused on find-
ing appropriate conditions for the acetylation and
tetrahydropyranylation of benzyl alcohol. According
to our findings, 1.2–1.5 mmol of Ac2O and 1.5 mmol
of DHP in the presence of 2 mole % of CMK-5-
SO3H under solvent-free reaction conditions at am-
bient temperature gave the best results and pro-
duced acetate and THP ethers of benzyl alcohol
in a short reaction time and quantitative yields
(Fig. 2). Lowering the catalyst 1 loading resulted
in lower yields. Furthermore, there is no consider-
able reaction when benzyl alcohol was allowed to re-
act with Ac2O or DHP in the absence of a cata-
lyst.

D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
Table 3. Comparison of the catalytic efficiency of CMK-5-SO3H against other catalysts used for the protection of benzyl alcohol
Time Yield
719
T
Entry Protection
Catalyst (content in mole %)
Solvent
Reference
◦C min
%
1
2
Acetylation
Acetylation
CMK-5-SO3H (2)
Solvent-free rt 10
DMSO
rt 90 > 99 Yoon et al. (2008)b,c
Solvent-free 50 45
Solvent-free rt
97a Present workb
polymer supported Gd(OTf)3 (0.5)
3
4
Acetylation
Acetylation
cobalt(II) salen complex (1)
sulfuric acid ([3-(3-silicapropyl) sul-
fanyl]propyl)ester (0.002 g)
99 Rajabi (2009)d
96 Niknam and Saberi (2009)e
6
5
6
Tetrahydropyranylation CMK-5-SO3H (2)
Solvent free rt 30
96a Present work
92 Shimizu et al. (2004)f
Tetrahydropyranylation SO3H-functionalized amorphous silica CH2Cl2
(0.5)
rt 30
7
Tetrahydropyranylation carbon supported sulfuric acid (cata- CH2Cl2
lyst : alcohol mass ratio of 0.6 : 1)
40 150
98 Yang et al. (2008)g
a) Isolated yield; b) 1.5 mmol Ac2O was used; c) long reaction time; d) 5 mmol Ac2O was used at 50◦C; e) 1 mL Ac2O was used;
f ) p-methoxybenzyl alcohol was used as a substrate in toxic solvent (CH2Cl2); g) toxic solvent (CH2Cl2) and only recovered twice.
The application of catalyst 1 was also extended to
the tetrahydropyranylation of alcohols and phenols.
For this purpose, several primary alcohols were pro-
tected with DHP in the presence of catalytic amounts
of CMK-5-SO3H (2 mole %) at ambient temperature
and under solvent-free reaction conditions in good to
excellent yields (Table 2, entries 1–11). Aromatic al-
cohols possessing both electron-donating as well as
electron-withdrawing groups underwent tetrahydropy-
ranylation to afford the corresponding THP ethers.
Secondary aliphatic (Table 2, entries 12–16) and aro-
matic (Table 2, entry 17) alcohols, and phenol (Ta-
ble 2, entry 18) and its derivatives (Table 2, entries
19–22) were also converted to the related compounds
under similar reaction conditions.
The results of acetylation and tetrahydropyrany-
lation of alcohols with polymer supported Gd(OTf)3
(Yoon et al., 2008), cobalt(II) salen complex (Rajabi,
2009), sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)
ester (Niknam & Saberi, 2009), SO3H-functionalized
amorphous silica (Shimizu et al., 2004), and activated
carbon supported sulfuric acid (Yang et al., 2008) were
compared with those of the presented method (Ta-
ble 3). The results show that CMK-5-SO3H is a pow-
erful catalyst for the protection of alcohols. This may
be attributed to the high surface area of the ordered
nanostructure of CMK-5 and beneficial hydrophobic-
ity of the catalyst 1 in the catalysis of the acetylation
and tetrahydropyranylation reactions, especially un-
der solvent-free condition.
covered CMK-5-SO3H was directly reused in ten suc-
cessive runs with no significant decreases in its effi-
ciency, providing high yields of the respective prod-
ucts in both reactions. Compared with the traditional
methods using volatile solvents and non-recoverable
catalysts which are energy consuming and environ-
mentally malign, the easy recycling is an attractive
property of catalyst 1.
Conclusions
In conclusion, new efficient methods for the acety-
lation and tetrahydropyranylation of alcohols by
highly recoverable CMK-5-SO3H at ambient temper-
ature and under solvent-free reaction conditions have
been introduced. The present methods are quite gen-
eral as a wide range of structurally varied alcohols and
phenols underwent protection catalyzed by catalyst 1
to afford the corresponding esters and THP ethers in
excellent yields. It is apparent that excellent catalytic
capacity and outstanding stability of the catalyst, the
exceedingly simple work-up, and ready reutilization
of CMK-5-SO3H ensure an efficient synthesis route.
Thus, this method provides an efficient and environ-
mentally benign alternative to the reported methods
in terms of yield, reaction time, and work-up proce-
dure. Efforts are currently underway in our research
group to apply this hydrophobic ordered solid acid
in the construction of potentially valuable organic
molecules in H2O as a green solvent.
In view of green chemistry, efficient recovery and
reuse of catalysts are highly preferable. Overall, this
methodology offers the advantages of the catalyst’s
recyclability enabling its use without further purifi-
cation. Based on this concept, the reaction of benzyl
alcohol with Ac2O or DHP in the presence of catalyst
1 was studied. After the completion of the first run,
ethyl acetate was added and the catalyst 1 was iso-
lated from the reaction mixture by filtration. The re-
Acknowledgements. The authors acknowledge the Islamic
Azad University of Qaemshahr Research Councils for the sup-
port of this work.
Supplementary data
Experimental procedures, TGA, BJH, and N2
adsorption–desorption experiment results for CMK-
5 and CMK-5-SO3H, the spectra of some products,

720
D. Zareyee et al./Chemical Papers 67 (7) 713–721 (2013)
and general procedures for acetylation and tetrahy-
dropyranylation of alcohols are available. Supplemen-
tary data associated with this article can be found in
the online version of this paper (DOI: 10.2478/s11696-
013-0369-x).
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