SO42-/SnO2: Efficient, chemoselective, and reusable catalyst for acylation of alcohols, phenols, and amines at room temperature

Article abstract of DOI:10.1080/00397910701354723

SO42-/SnO2 was employed for the acylation of a variety of alcohols, phenols, and amines under solvent-free conditions at room temperature. This method showed preferential selectivity for acetylation of the amino group in the presence of a hydroxyl group. The reported method is simple, mild, and environmentally viable, using several other acid anhydrides at room temperature. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701354723

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2-
SO4 /SnO2: Efficient, Chemoselective, and
Reusable Catalyst for Acylation of Alcohols,
Phenols, and Amines at Room Temperature
Jitendra R. Satam a , Manoj B. Gawande a , Sameer S. Deshpande a & Radha
V. Jayaram a
a Department of Chemistry , University Institute of Chemical Technology ,
Nathalal Parekh Road, Matunga, Mumbai, India
Published online: 30 Aug 2007.
To cite this article: Jitendra R. Satam , Manoj B. Gawande , Sameer S. Deshpande & Radha V. Jayaram (2007)
SO4 2-/SnO2: Efficient, Chemoselective, and Reusable Catalyst for Acylation of Alcohols, Phenols, and Amines
at Room Temperature, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 37:17, 3011-3020, DOI: 10.1080/00397910701354723
To link to this article: http://dx.doi.org/10.1080/00397910701354723
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Synthetic Communicationsw, 37: 3011–3020, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701354723
SO242/SnO2: Efficient, Chemoselective, and
Reusable Catalyst for Acylation of Alcohols,
Phenols, and Amines at Room Temperature
Jitendra R. Satam, Manoj B. Gawande, Sameer S. Deshpande,
and Radha V. Jayaram
Department of Chemistry, University Institute of Chemical Technology,
Mumbai, India
Abstract: SO242/SnO2 was employed for the acylation of a variety of alcohols,
phenols, and amines under solvent-free conditions at room temperature. This method
showed preferential selectivity for acetylation of the amino group in the presence of
a hydroxyl group. The reported method is simple, mild, and environmentally viable,
using several other acid anhydrides at room temperature.
Keywords: acetylation, acylation, chemoselective, room temperature
INTRODUCTION
The acylation of alcohols and phenols is a fundamental process in organic
chemistry. It also provides an efficient route for protecting -OH groups
during oxidation, peptide coupling, and glycosidation reactions.[1] This -OH
group protection is commonly achieved through acylation with acetic
anhydride because of the ease of deprotection.[2] The various catalysts
developed for acylation include nucleophilic agents[3] such as 4-dimethyl-
aminopyridine (DMAP) and Bu3P; Lewis acids such as metal halides,[4]
metal triflates,[5] and metal perchlorates;[6] ionic liquids;[7] and several solid
acids such as clays, zeolite, yttria-zirconia and Naffion-H.[8] Some of these
Received in India October 27, 2006
Address correspondence to Radha V. Jayaram, Department of Chemistry, Univer-
sity Institute of Chemical Technology, Nathalal Parekh Road, Matunga, Mumbai
400 019, India. E-mail: rvjayaram@hotmail.com; jiten_uict@yahoo.co.in
3011

3012
J. R. Satam et al.
catalytic systems are homogeneous and nonrecoverable and suffer from limit-
ations such as longer reaction times, stringent conditions, use of halogenated
solvents, and hazardous materials (e.g., DMAP is highly toxic [LD50 in the rat
intravenous: 56 mg/kg],[9] Bu3P is inflammable [flash point: 378C] and air
sensitive; perchloric acid and its salts are potentially explosive; and triflates
are not cost effective). In recent years, there has been a tremendous upsurge
of interest in various chemical transformations performed under hetero-
geneous catalysis.[10]
SO242/SnO2 have been used for various organic transformations because of
its ease in preparation and higher activity.[11] SO422/SnO2 was prepared by
standard procedures.[12] The reaction conditions were standardized after con-
ducting the acetylation of 2-naphthol with Ac2O using various solvents at
room temperature (Table 1). Excellent yield was obtained under neat conditions
with 0.5 mol% of the catalyst with an equivalent amount of Ac2O, so we have
continued the reactions under solvent-free conditions. To explore the scope and
activity of the catalyst, various alcohols, phenols, and amines with electron-
donating and electron-withdrawing groups were studied. We have observed
that acetylation of phenols was slightly slower than that of alcohols and
amines. No competitive Fries rearrangement was observed in the case of
phenolic substrates. The efficacy of the catalyst can be clearly visualized in
the acetylation of polyhydroxy compounds under similar conditions (Table 2,
entries 3–5). Another noteworthy feature of this methodology is that polyols
such as D-mannitol underwent exhaustive acetylation, demonstrating the
practical utility of this method (Table 2, entry 3).
The present procedure is excellent for the acetylation of alcohols
(primary and secondary), phenols, amines, and bifunctional compounds
containing -NH2 and -OH groups. To examine the chemoselectivity of the
Table 1. Effect of solvent during the SO242/SnO2-catalyzed
acetylation of 2-naphthol with Ac2O using different solvents
Entry
Mol (%)
Solvent
Time
Yield (%)a,b
1
2
3
4
5
0.5
0.5
0.5
0.5
0.5
CH3CN
THF
2 h
2 h
82
50
80
84
95
PhCH3
CH2Cl2
Neat
2 h
2 h
30 min
aThe substrate was treated with Ac2O (1 equiv.).
bIsolated yield of the corresponding acetylated product.

Table 2. Acetylation of heteroatom using SO242/SnO2 and Ac2O at room temperaturea
Bp (Torr) or mp (8C)
Entry
Substrate (RXH)
Time (min)
Yield (%)b,c
Product (RXAc)d
Found
Reported
1
2
3
4
5
R ¼ CH3(CH2)7, X ¼ O
R ¼ Ph CH2, X ¼ O
Ethylene glycol
D-Mannitol
10
10
45
15
30
95
R ¼ CH3(CH2)7, X ¼ O
R ¼ Ph CH2, X ¼ O
100–101
212–213
120–121
186–188
259–260
98–99[13]
214–215[14]
123–124[14]
186[15]
94
94g
90e
90f
Hexa-O-acetyl-D-Mannitol
Ethane-1,2-diyl diacetate
Propane-1,2,3-triyl triacetate
Glycerol
258[16]
6
7
R1 ¼ R2 ¼ R3 ¼ H
30
60
88
90
R1 ¼ R2 ¼ R3 ¼ H, X ¼ OAc
R1 ¼ R2 ¼ H, R3 ¼ NO2,
X ¼ OAc
194
79–81
196[14]
R1 ¼ R2 ¼ H, R3 ¼ NO2
81–82[14]
8
9
R1 ¼ R2 ¼ H, R3 ¼ Br
R1 ¼ R2 ¼ H, R3 ¼ Cl
R3 ¼ R2 ¼ H, R1 ¼ Me
R3 ¼ R2 ¼ H, R1 ¼ OMe
1-Naphthol
45
30
20
30
60
88
88
94
90
90
R1 ¼ R2 ¼ H, R3 ¼ Br,
X ¼ OAc
235–237
226–228
210–211
105–107
45–47
237–240[14]
226–228[14]
208[14]
R1 ¼ R2 ¼ H, R3 ¼ Cl,
X ¼ OAc
10
11
12
R3 ¼ R2 ¼ H, R1 ¼ Me,
X ¼ OAc
R3 ¼ R2 ¼ H, R1 ¼ OMe,
X ¼ OAc
107[14]
1-Naphthyl acetate
48–49[14]
(continued)

Table 2. Continued
Bp (Torr) or mp (8C)
Entry
13
Substrate (RXH)
Time (min)
30
Yield (%)b,c
95
Product (RXAc)d
2-Naphthyl acetate
Found
Reported
70[14]
2-Naphthol
68–69
14
15
16
17
R1 ¼ R2 ¼ H
R1 ¼ NO2, R2 ¼ H
R1, R2 ¼ NO2
PhCH2NH
5
20
30
20
95
90
88
94
R1 ¼ R2 ¼ H
163–165
92–93
119
164–165[14]
94[14]
R1 ¼ NO2, R2 ¼ H
R1, R1 ¼ NO2
PhCH2NHAc
121[14]
61
61[14]
aThe substrate was treated with Ac2O (1 equiv. per OH/NH2 group except for entries 3, 4, and 5) in the presence of SO422/SnO2 (0.5 mol%) under
neat conditions at room temperature.
bIsolated yield of the corresponding acetylated product.
cThe unreacted substrate was recovered.
1
dAll compounds have been satisfactorily characterized (IR, H NMR).
eIsolated yield of the di-acetate.
fIsolated yield of the tri-acetate.
gIsolated yield of the hexa-acetate.

SO242/SnO2 as Catalyst
3015
present method, bifunctional substrates containing -NH2 and -OH groups were
studied (Table 3). Selective acetylation of the -NH2 group in the presence of
the -OH group was observed at room temperature with 1 equivalent of acetic
anhydride to give corresponding N-acetate product, and no O-acetate product
was found under this conditions. This might be due to more nucleophilicity of
amines than phenols. The scope of this methodology was further extended by
acylation of alcohols, phenols, and amines with variety of other acid anhy-
drides. Thus, acylation of octanol, phenol, and aniline can be achieved with
different anhydrides such as (PhCO)2O, succinic anhydride, and phthalic
anhydride (Table 4, entries 1–5). The reactions were performed in MeCN
at room temperature. It should be noted that the catalyst is reusable for five
cycles without significant loss of its efficacy. Unreacted substrate can be
recovered. The product obtained does not need much purification.
In conclusion, SO242/SnO2 is found to be a new, highly efficient, chemo-
selective, and reusable catalyst for acylation of primary and secondary
alcohols, phenols, and amines. With the increasing tight legislation on the
release of waste and use of toxic substances as a measure to control environ-
mental pollution,[21] the use of a stoichiometric amount of acetylating agent
and the solvent-free conditions employed in the present method make it envi-
ronmentally friendly and suitable for industrial applications.
EXPERIMENTAL
Typical Procedure for the Acetylation
2-Naphthol (0.720 g, 5 mmol) was treated with Ac2O (0.48 mL, 5 mmol)
under neat conditions at rt for 30 min under magnetic stirring in the
presence of SO242/SnO2 (0.5 mol%) with respect to substrate. The course
of the reaction was monitored by thin-layer chromatography (TLC) and
gas chromatography (GC). The reaction mixture was diluted with Et2O
(20 mL), and the solution was filtered to separate the catalyst. The filtrate
was washed successively with 1% aqueous NaOH (15 mL) and brine
(15 mL), dried (Na2SO4), and concentrated to afford the product, which
1
was in full agreement with the mp and spectral data (IR, H NMR) of an
authentic sample of 2-acetoxynaphthalene (0.883 g, 95% with SO242/
SnO2). The catalyst was recovered and reused for a fresh lot of
2-hydroxynaphthalene.
Data
Hexa-O-acetyl-D-mannitol (Table 2, entry 3).[15] Found: [a]2D5 ¼ þ34.4
(c 1.2 CHCl3); [a]2D5 ¼ þ27 (c 1.0 CHCl3). 1H NMR (CDCl3): d 2.06
(s, 6H), 2.10 (s, 6H), 4.10 (m, 4H), 5.05 (m, 2H), and 5.44 (m, 2H).

Table 3. Chemoselective N-acetylation of bifunctional substrates using SO242/SnO2 under solvent-free conditions at room temperaturea
Bp (Torr) or mp (8C)
Time
(min)
Entry
Substrate
Yield (%)b,c
Productd
Found
Reported
1
2
3
4
R1 ¼ NH2,
15
20
10
15
90
90
90
88
R1 ¼ NHAc,
126–127
167–169
62–64
129–130[14]
169–170.5[14]
63–65[14]
R2 ¼ R3 ¼ H
R1 ¼ R2 ¼ H;
R3 ¼ NH2
R2 ¼ R3 ¼ H
R1 ¼ R2 ¼ H;
R3 ¼ NHAc
2-Amino ethanol
N-(2-Hydroxyethyl
acetamide)
2-Amino-1-propanol
N-(2-Hydroxypropyl
acetamide)
95–98
96–99[14]
aThe substrate was treated with Ac2O (1 equiv. per OH/NH2 group) in the presence of SO422/SnO2 (0.5 mol%) under neat conditions at room
temperature.
bIsolated yield of the corresponding acetylated product.
cThe unreacted substrate was recovered.
dAll compounds have been satisfactorily characterized (IR, 1H NMR).

Table 4. Acylation of alcohols, phenols, and amines with acid anhydrides in the presence of SO242/SnO2 (0.5 mol%) in MeCN at room temperaturea
Bp (Torr) or mp (8C)
Entry
1
Substrate (RXH)
Acid anhydride
Time (h) Yield (%)b,c
Product (ROCOR1)
Found
Reported
304[17]
R ¼ CH3(CH2)7, X ¼ O (PhCO)2O
3
90
R ¼ CH3(CH2)7,
R1 ¼ Ph
302–303
2
3
4
5
R ¼ CH3(CH2)7, X ¼ O Phthalic anhydrided
12
6
90d
94
93d
95
Dioctyl phthalate
Phenyl benzoate
Diphenyl succinate
Benzanilide
380
68–69
380[18]
71[14]
120–121[19]
164–165[20]
R ¼ Ph, X ¼ O
R ¼ Ph, X ¼ O
PhNH2
(PhCO)2O
Succinic anhydrided
(PhCO)2O
6
120–121
163–165
1
aThe substrate was treated with Ac2O (1 equiv. per OH/NH2 group) in the presence of SO422/SnO2 (0.5 mol%) at room temperature.
bIsolated yield of the corresponding acylated product.
c The unreacted substrate was recovered.
dAcid anhydride–substrate (1:2).

3018
J. R. Satam et al.
Ethane-1,2-diyl diacetate (Table 2, entry 4).[22] IR (neat): 2934, 1730, 1380,
1
1245 cm21. H NMR (CDCl3): d 2.03 (s, 6H) and 4.21 (s, 4H).
Propane-1,2,3-triyl triacetate (Table 2, entry 5).[22] IR (neat): 2935, 1730,
1
1370, 1240 cm21. H NMR (CDCl3): d 2.05 (s, 3H), 2.07 (s, 6H), 4.30
(m, 4H), and 5.23 (m, 1H).
N-(2-Hydroxyphenyl acetamide) (Table 3, entry 1).[22] IR (neat): 3447,
1
2980, 1740 cm21. H NMR (CDCl3): d 2.08 (s, 3H), 6.86 (m, 3H), 7.65
(1H, d) 9.27 (br, 1H), and 9.67 (s, 1H).
N-(4-Hydroxyphenyl acetamide) (Table 3, entry 2).[22] IR (neat): 3380,
1
3070, 2850, 1697, 1570, 1280 cm21. H NMR (CDCl3): d 2.08 (s, 3H),
6.55–6.67 (m, 3H), 7.22 (d, 1H), 8.95 (br, 1H), and 9.55 (s, 1H).
N-(2-Hydroxethyl acetamide) (Table 3, entry 3).[22] IR (neat): 3303, 3097,
1
2935, 1705, 1250, 1066 cm21. H NMR (CDCl3): d 1.93–2.03 (d, 3H), 3.35
(m, 2H), 3.7 (m, 2H), 5.18 (bs, 1H), 6.67 (s, 1H).
Dioctyl phthalate (Table 4, entry 2).[22] IR (neat): 2990, 2953, 1760,
1
1120 cm21. H NMR (CDCl3): d 0.88 (t, 6H), 1.25–1.32 (m, 16H), d 1.40
(quintet, J ¼ 7.0, 4H), 1.73 (quintet, J ¼ 7.0, 4H), 4.30 (t, J ¼ 7.0, 4H),
7.50–7.54 (m, 2H).
ACKNOWLEDGMENTS
The authors are thankful to Regional Sophisticated Instrumental-analysis
Centre (RSIC), Indian Institute of Technology, Mumbai, for providing the
1H NMR facility.
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