Poly-(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) and N,N,N′,N′- tetrabromobenzene-1,3-disulfonamide as highly efficient catalysts, and (AC2O/SIO2) as a heterogeneous system for the acetylation of alcohols, amines, and thiols under microwave irradiation

Article abstract of DOI:10.1080/10426507.2010.496277

Chemical Equation Presented Poly-(N,N′-dibromo-N-ethyl-benzene-1,3- disulfonamide) (PBBS) and N,N,N′,N′-tetrabromobenzene-1,3- disulfonamide (TBBDA) are good activators and catalytic reagents for the acetylation of alcohols, amines, and thiols. The presented method has the advantages of mild conditions, chemoselectivity, and good to high yields, and uses noncorrosive, inexpensive, recyclable, and environmentally friendly catalysts. We have also demonstrated that combining SiO2 with microwave energy provides an efficient, fast, convenient, and easy workup procedure for the synthesis of mono- and disubstituted acetates, acetamides, and thioacetamides. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2010.496277

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Poly-(N,N′-dibromo-N-ethyl-
benzene-1,3-disulfonamide) and
N,N,N′,N′- Tetrabromobenzene-1,3-
disulfonamide as Highly Efficient
Catalysts, and (AC O/SIO ) as a
2
2
Heterogeneous System for the
Acetylation of Alcohols, Amines, and
Thiols Under Microwave Irradiation
a
b
b
Hojat Veisi , Ramin Ghorbani-Vaghei , Hosna Eskandari , Saba
a
b
a
Hemmati , Ardashir Rezaei , Somaye Hajinazari , Mohammad
a
a
Raoof Heidari Far & Azam Entezari
a
Department of Chemistry, Payame Noor University (PNU), Iran
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina
b
University, Hamedan, Iran
Published online: 19 Feb 2011.
To cite this article: Hojat Veisi , Ramin Ghorbani-Vaghei , Hosna Eskandari , Saba Hemmati , Ardashir
Rezaei , Somaye Hajinazari , Mohammad Raoof Heidari Far & Azam Entezari (2011): Poly-(N,N′-
dibromo-N-ethyl-benzene-1,3-disulfonamide) and N,N,N′,N′- Tetrabromobenzene-1,3-disulfonamide
as Highly Efficient Catalysts, and (AC O/SIO ) as a Heterogeneous System for the Acetylation of
2
2
Alcohols, Amines, and Thiols Under Microwave Irradiation, Phosphorus, Sulfur, and Silicon and the
Related Elements, 186:2, 213-219
To link to this article: http://dx.doi.org/10.1080/10426507.2010.496277
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Phosphorus, Sulfur, and Silicon, 186:213–219, 2011
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.496277
COMMUNICATION
ꢁ
POLY-(N,N -DIBROMO-N-ETHYL-BENZENE-1,3-
ꢁ
ꢁ
DISULFONAMIDE) AND N,N,N ,N -
TETRABROMOBENZENE-1,3-DISULFONAMIDE AS
HIGHLY EFFICIENT CATALYSTS, AND (AC O/SIO ) AS A
2
2
HETEROGENEOUS SYSTEM FOR THE ACETYLATION OF
ALCOHOLS, AMINES, AND THIOLS UNDER MICROWAVE
IRRADIATION
1
2
2
Hojat Veisi, Ramin Ghorbani-Vaghei, Hosna Eskandari,
1
2
1
Saba Hemmati, Ardashir Rezaei, Somaye Hajinazari,
1
1
Mohammad Raoof Heidari Far, and Azam Entezari
1
Department of Chemistry, Payame Noor University (PNU), Iran
2
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University,
Hamedan, Iran
GRAPHICAL ABSTRACT
3
method A: TBBDA, Ac O, rt, CH CN
'
2
'
RR XH
RR XAc
3
method B: PBBS, Ac O, rt, CH CN
2
method C: Microwave, Ac O/ SiO2
2
X: O, S, NH
R: H, alkyl or aryl
'
R : alkyl or aryl
Br
N
Br
Br
Br
N
)
N
Br
N
S
S
Br
CH
2
CH2
)
S
S
O
O
O
O
n
O
O
O
O
PBBS
TBBDA
ꢀ
ꢀ
ꢀ
Abstract Poly-(N,N -dibromo-N-ethyl-benzene-1,3-disulfonamide) (PBBS) and N,N,N ,N -
tetrabromobenzene-1,3-disulfonamide (TBBDA) are good activators and catalytic reagents for
the acetylation of alcohols, amines, and thiols. The presented method has the advantages of
mild conditions, chemoselectivity, and good to high yields, and uses noncorrosive, inexpensive,
recyclable, and environmentally friendly catalysts. We have also demonstrated that combining
SiO2 with microwave energy provides an efficient, fast, convenient, and easy workup procedure
for the synthesis of mono- and disubstituted acetates, acetamides, and thioacetamides.
Keywords Acetylation; microwave irradiation; PBBS; room temperature; TBBDA
Received 28 March 2010; accepted 24 May 2010.
Address correspondence to Hojat Veisi, Department of Chemistry, Payame Noor University (PNU), Iran.
E-mail: hojatveisi@yahoo.com
2
13

2
14
H. VEISI ET AL.
INTRODUCTION
Protection of alcohols, amines, and thiols using acid anhydrides is of great in-
terest to synthetic chemists, and has been applied extensively by organic chemists for
1
over a century. For this purpose, catalysts are used for rapid and efficient acylations.
2
Although 4-(dimethylamino)pyridine (DMAP), 4-pyrrolidinopyridine (PYY), and pyri-
3
dine are the most commonly used catalysts for acylations, other catalysts such as
4
5
6
7
8
9
Al(OTf)3, La(NO3)3.6H2O, 3-nitrobenzeneboronic acid, I2, Cu(BF4)2·xH2O, ZrCl4,
10
11
12
13
14
15
16
AlPW12O40, TMSOTf, Sc(OTf)3, NBS, ionic liquids, CeCl3, ZrOCl2·8H2O,
HClO4/SiO2,17 Zeolite, Montmorillonite K-10 and KSF, and InI3 have been used for
the acetylation of alcohols, amines, and thiols. However, many of these methods require
prolonged reaction times and give rise to metal waste products. Thus, a milder, selective,
nonhazardous, and inexpensive method is still in demand.
18
19
20
RESULTS AND DISCUSSION
In this article, we report a convenient method for the O,N,S-acetylation of al-
ꢀ
cohols, amines, and thiols with acetic anhydride using poly-(N,N -dibromo-N-ethyl-
ꢀ
ꢀ
benzene-1,3-disulfonamide) (PBBS) and N,N,N ,N -tetrabromobenzene-1,3-disulfonamide
2
1–26
(TBBDA)
as recyclable catalytic reagents at room temperature. In addition, we suc-
ceeded in the rapid, high yield preparation of acetates, acetamides, and thioacetamides
using Ac2O/SiO2 under solvent-free conditions by microwave irradiation (Scheme 1).
method A: TBBDA, Ac O, rt, CH CN
2
3
'
'
RRXH
RRXAc
method B: PBBS, Ac O, rt, CH CN
2
3
method C: Microwave, Ac O
/
SiO2
2
X: O, S, NH
R: H, alkyl or aryl
'
R : alkyl or aryl
Br
Br
N
Br
Br
)
N
S
Br
N
S
N
Br
CH2
CH2
)
n
S
S
O
O
O
O
O
O
O
O
PBBS
TBBDA
Scheme 1
To explore the generality and scope of this reaction, a wide range of structurally
varied alcohols, amines, and thiols were subjected to acetylation by these procedures. The
results are reported in Table 1. In this manner, we have succeeded in developing convenient
and efficient procedures for the preparation of acetamides (Table 1, entries 1–10). Table 1
shows that the yields are good to excellent. It was found that secondary amines (Table 1,
entries 5–8) undergo smooth acetylation and give the desired acetamides. No selectivity
between primary and secondary amino groups during the reactions was observed (Table I,
entry 9).
In a similar manner, various substituted aromatic and aliphatic hydroxy compounds
and thiols were acetylated very smoothly under mild reaction conditions and gave the
desired O,S-acetylated alcohols, phenols, and thiols with high yields. The procedures are
uniformly effective for the acetylation of primary saturated alcohols (Table 1, entries 25

ACETYLATION OF ALCOHOLS, AMINES, AND THIOLS
215
Table 1 Acetylation of alcohols, amines, and thiols using TBBDA (method A), PBBS (method B), and a
heterogeneous (Ac2O/SiO2) system under microwave irradiation (method C)
Method A
Time (min)/
yield (%)
Method B
Time (min)/
yield (%)
Method C
Time (min)/
yield (%)
Entry
1
Amine (1)
Product
(3)/99
(10)/95
(10)/94
(60)/97
(75)/90
(60)/92
(1)/99
(3)/99
2
3
(1.5)/98
4
(100)/85
(120)/82
(3)/98
5
6
(20)/99
(35)/92
(40)/95
(60)/90
(2.5)/99
(2.5)/98
7
8
9
(10)/98
(4)/99
(25)/96
(5)/98
(1.5)/99
(2)/100
(4)/98
(20)/90
(25)/90
1
1
1
0
1
2
(10)/98
(120)/80
(145)/80
(15)/95
(180)/75
(180)/70
(3)/98
(4)/99
(4)/99
1
1
3
4
(240)/70
(180)/99
(300)/70
(240)/85
(3.5)/98
(3)/98
1
5
(120)/78
(240)/62
(3.5)/99
1
1
1
6
7
8
(180)/50
(240)/100
(60)/98
(360)/67
(480)/98
(240)/85
(3.2)/100
(4)/99
(2)/99
(
Continued on next page)

2
16
H. VEISI ET AL.
Table 1 Acetylation of alcohols, amines, and thiols using TBBDA (method A), PBBS (method B), and a
heterogeneous (Ac2O/SiO2) system under microwave irradiation (method C) (Continued)
Method A
Time (min)/
yield (%)
Method B
Time (min)/
yield (%)
Method C
Time (min)/
yield (%)
Entry
Amine (1)
Product
1
9
(60)/99
(180)/99
(2.5)/99
2
2
0
1
(60)/87
(60)/99
(240)/92
(180)/85
(1.5)/98
(2)/98
2
2
2
3
No Reaction
No Reaction
No Reaction
No Reaction
(2)/99
(2)/98
2
2
2
4
5
6
(120)/95
(160)/90
(260)/85
(150)/90
(180)/85
(300)/80
(2)/98
(3.5)/99
(3.5)/99
2
2
7
8
(120)/97
(240)/98
(240)/83
(240)/80
(2)/96
(3)/98
2
3
9
0
(120)/94
(240)/99
(3)/97
No Reaction
No Reaction
(3.5)/99
and 29), an allylic alcohol (Table 1, entry 24), benzylic alcohols (Table 1, entries 18–21),
secondary alcohols (Table 1, entries 26–28), phenols (Table 1, entries 22 and 23), and thiols
(
Table 1, entries 11–17). During this reaction, we did not observe chemoselectivity for
compounds with two different functional groups such as NH, SH, and OH (Table 1, entries
1 and 12).
Several attempts to acetylate a tertiary alcohol (Table 1, entry 30) using PBBS and
TBBDA in the presence of a solvent (acetonitrile) failed. As shown in Table 1, adamantan-
-ol was however acetylated with excellent yield by using Ac2O/SiO2 under microwave
irradiation.
1
1

ACETYLATION OF ALCOHOLS, AMINES, AND THIOLS
217
Since these reagents contain bromine atoms, which are attached to nitrogen atoms,
+
it is very likely that they release Br in situ, which can act as a Lewis acid in the reaction
medium. We expected that this would be sufficient to catalyze the acetylation of alcohols,
amines, and thiols.2
1–26
We observed that PBBS and TBBDA were recyclable catalysts for the acetylation,
and the catalytic activities of the reagents after several runs were almost the same as those
of fresh catalysts.
This methods is mild and compatible with various functional groups such as chloro
(Table 1, entries 20 and 21), bromo (Table 1, entry 19), and methoxy (Table 1, entry 2)
groups present in the substrate. In general, the acetylations are reasonably fast and clean.
No side products were isolated in any reaction.
The method was found to be highly selective for primary alcohols with TBBDA and
PBBS as catalysts at room temperature. In a mixture of benzyl alcohol and phenol, the
primary alcohol was completely converted to the corresponding product (Table 2, entry 1).
Similarly, benzyl alcohol was acetylated in the presence of cyclohexanol, adamantan-1-ol,
and benzylthiol at room temperature (Table 2, entries 2–4).
The advantages of our methods as compared with common methods for the acetylation
of benzyl alcohol, benzylthiol, and adamantan-1-ol are shown in Table 3.
Table 2 Competitive acetylation reactions of alcohols with TBBDA (method A) and PBBS (method B)
Entry
1
Mixture
Product
Time (h)
1b or 4c
Conversion (%)a
100
0
2
1b or 4c
100
0
3
4
1b or 4c
90
1
0
1b or 4c
100
0
a
The conversion was detected by TLC and NMR spectroscopy.
The conversion was complied with TBBDA.
b
c
The conversion was complied with PBBS.

2
18
H. VEISI ET AL.
Table 3 Reaction times and yields for previously published methods
Substrate
Conditions
Reaction time
Yield (%)
Ref.
Benzyl alcohol
Benzyl alcohol
Benzyl alcohol
Benzylthiol
InI3/reflux
14 h
4 h
1 h
3 min
37 h
100 min
18 h
82
94
90
89
90
92
81
20
13
19
10
13
10
27
NBS/CH2Cl2/rt
K-10 or KSF/rt
AlPW12O40/rt
NBS/CH2Cl2/rt
AlPW12O40/rt
Sc(OTf)3/reflux
1-Adamantanol
1-Adamantanol
1-Adamantanol
CONCLUSIONS
In conclusion, we have demonstrated that PBBS and TBBDA are good activators
catalytic reagents) for the acetylation of alcohols, amines, and thiols. The present method
(
exhibits the additional advantages of mild conditions, chemoselectivity, and good to high
yields, and it uses noncorrosive, inexpensive, recyclable, and environmentally friendly
catalysts. We have also demonstrated that combining SiO2 with microwave energy provides
an efficient, fast, convenient, and easy workup procedure for the synthesis of mono- and
disubstituted acetates, acetamides, and thioacetamides. Moreover, this protocol introduces
a practical and viable green technology of solvent-free reactions.
EXPERIMENTAL
General Procedure for the Acetylation of Alcohols, Amines, and Thiols
by Using PBBS and TBBDA (Methods A and B)
To a solution of the amine, thiol, or alcohol (1 mmol) and acetic anhydride (1 mmol) in
CH3CN (2 mL) at room temperature, the activator (PBBA, 0.1 g or TBBDA, 0.1 mmol, 0.05
g) was added. The mixture was stirred at this temperature for the period of time specified in
Table 1. The reaction was monitored by TLC (hexane/acetone, 4:1). After completion of the
reaction, the solvent was evaporated. Then CH2Cl2 (10 mL) was added, and the reagents
were removed by filtration. Evaporation of the solvent under reduced pressure gave the
products. Further purification was achieved by TLC (hexane/acetone, 7:3).
Preparation of the Ac2O/SiO2 Reagent
Acetic anhydride (1 mL) was added to 1 g of silica gel (mesh 70–230) with stirring
for 1 min at room temperature.
General Experimental Procedure for the Acetylation of Alcohols,
Amines, and Thiols with Ac2O/SiO2 Under Microwave Irradiation (Method C)
The amine, thiol, or alcohol (1 mmol) and the above compounds were mixed thor-
oughly and then subjected to the 100% power radiation of a domestic microwave oven (LG
Co. microwave, 230 v ∼ 50 Hz, RF output 900 W) for a certain period of time (Table 1).
The progress of each reaction was monitored by TLC. After completion of the reaction, the
obtained mixture was allowed to cool, was diluted with ethanol, and filtered to remove the

ACETYLATION OF ALCOHOLS, AMINES, AND THIOLS
219
silica gel. Evaporation of the solvent under reduced pressure gave the pure product with
excellent yield (96–100%).
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