AlCl3·6H2O/KI/CH3CN/H 2O: An efficient and versatile system for chemoselective C-O bond cleavage and formation of halides and carbonyl compounds from alcohols in hydrated media

Article abstract of DOI:10.1080/00397910500516316

AlCl₃·6H₂O/KI/CH₃CN/H ₂O, an efficient and versatile system, cleaves the C-O bonds of esters, acetals, ethers, and oxathiolanes to the corresponding acids, alcohols, and carbonyl compounds chemoselectively at 80°C in hydrated media with good yields. This system also converts the alcohols (primary/secondary) to halides and oxidizes the alcohols (primary/secondary) to the corresponding carbonyl compounds in the presence of DMSO. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500516316

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AlCl · 6H O/KI/CH CN/H O: An Efficient and
3
2
3
2
Versatile System for Chemoselective C–O
Bond Cleavage and Formation of Halides
and Carbonyl Compounds from Alcohols in
Hydrated Media
a
a
b
Dilip Konwar , Saikat Das Sharma , Prodip Kumar Gogoi & Pranjal Gogoi
a
a
Organic Chemistry Division , Regional Research Laboratory , Jorhat, Assam,
India
b
Department of Chemistry , Dibrugarh University , Dibrugarh, Assam, India
Published online: 24 Feb 2007.
To cite this article: Dilip Konwar , Saikat Das Sharma , Prodip Kumar Gogoi & Pranjal Gogoi (2006)
AlCl · 6H O/KI/CH CN/H O: An Efficient and Versatile System for Chemoselective C–O Bond Cleavage and
3
2
3
2
Formation of Halides and Carbonyl Compounds from Alcohols in Hydrated Media, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:9, 1259-1264, DOI:
10.1080/00397910500516316
To link to this article: http://dx.doi.org/10.1080/00397910500516316
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Synthetic Communications , 36: 1259–1264, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500516316
.
AlCl 6H O/KI/CH CN/H O: An Efficient
3
2
3
2
and Versatile System for Chemoselective
C–O Bond Cleavage and Formation of
Halides and Carbonyl Compounds from
Alcohols in Hydrated Media
Pranjal Gogoi, Dilip Konwar, and Saikat Das Sharma
Organic Chemistry Division, Regional Research Laboratory,
Jorhat, Assam, India
Prodip Kumar Gogoi
Department of Chemistry, Dibrugarh University, Dibrugarh,
Assam, India
.
Abstract: AlCl
3
6H
2
O/KI/CH
3
CN/H
2
O, an efficient and versatile system, cleaves
the C–O bonds of esters, acetals, ethers, and oxathiolanes to the corresponding
acids, alcohols, and carbonyl compounds chemoselectively at 80 8C in hydrated
media with good yields. This system also converts the alcohols (primary/secondary)
to halides and oxidizes the alcohols (primary/secondary) to the corresponding
carbonyl compounds in the presence of DMSO.
.
Keywords: AlCl
3
6H
2
O/KI/CH
halide formation and oxidation, hydrated media, system
3
CN, chemoselective, cleavage of C–O bonds,
The protection–deprotection of functional groups serves a fundamental role in
[
1]
organic chemistry. A number of efficient reagents are reported for the
cleavage of C–O bonds under heterogeneous and homogeneous conditions.
[
2]
[3]
[4]
The heterogeneous reagents
include Al O ,
2
mont. K10,
3
Received October 6, 2005
Address correspondence to Dilip Konwar, Organic Chemistry Division, Regional
Research Laboratory, Jorhat, Assam, India. E-mail: dkonwar@yahoo.co.uk
1
259

1
260
P. Gogoi et al.
[
5]
[6]
[7]
[8]
[9]
K CoW O 3H O, (P)-DCKA, SiO /CAN, Pd/C, sulfated SnO2,
5
12 40
2
2
[
10]
and Dowex 50WX8.
C–O bonds include mineral acids,
The homogeneous reagents used for the cleavage of
[12]
[11]
[13]
Me SiI,
3
[15]
BF3 etherate-I,
[16]
.
Hg(OAc)2 KSCN,
[
14]
.
TiCl4 LiI,
pyridinium
and NaSePh.
tosylate,
This transformation could also be
[
17]
[18]
.
Me SiSiMe I ,
2
3
3
[19]
achieved by using enzymatic methods.
In a previous communication, we reported that AlCl 6H O/KI/CH CN
is an efficient system for dehydration
Beckmann rearrangement, and the Bischler–Napieraliski reaction in hydrated
.
3
2
3
[20]
of oximes and amides to nitriles, the
media. The system could smoothly deoxygenate organic N-oxides to the
corresponding imines in hydrated media.
[21]
Here, we first demonstrate the
.
efficiency of AlCl3 6H O/KI/CH CN/H O for chemoselective C–O bond
2
3
2
cleavage of esters, ethers, and acetates and formation of halides and
carbonyl compounds from alcohols in hydrated media.
The reagent system cleaved the C–O bonds of esters, (Table 1 entries
1
–4) and acetates (entries 5–11) to the corresponding acids and phenols
respectively. The acetate groups were chemoselectively cleaved when both
the acetate and ester groups were present within the same molecules
(
entries 8 and 9). The ester/acetate groups preferentially cleaved when one
of these functionalities were present with ether functionality within the
substrate (entries 10 and 11). The oxathiolanes were cleaved to the corre-
sponding carbonyl compounds (entries 13–18), and the system chemoselec-
tively cleaved the oxathiolanes when both the acyclic acetals/ketals and
oxathiolanes were present within the substrates (entries 15–18). In all the
cases, the optimum ratio of water and acetonitrile was 1:10. The system
converted the primary alcohols (entries 19–22) to the corresponding halides
in very good yields. The cleavage of C–O bonds of these substrates with
HI proceeded with lower yields and required more time.
The system in the presence of DMSO oxidized selectively both the
primary (entries 23–26) and the secondary (entry 27) alcohols to the corre-
sponding carbonyl compounds (Table 2).
Regarding the mechanism of the reactions, it may be proposed that
[
20–22]
.
AlCl3 6H O is in reality
[Al(H O) ]Cl , which reacts with KI to
2 6 3
2
2
þ
þ
2
3I [A] or
form [Al(H O) ]I , which can exist as [Al(H O) (OH)]
þ
H
Al(H O) (OH) ] 2H 3I [B] and so forth in solution. The liberated
2
6
3
þ
2
5
2
[
2
4
2
proton forms HI and in the presence of aluminium cleaves C–O bonds of
esters to the corresponding acids as shown below (Scheme 1).
.
In summary the utility of AlCl3 6H O/KI/CH CN/H O for various
2
3
2
transformations has been successfully demonstrated.
EXPERIMENTAL
1
H NMR spectra were recorded at 60 MHz. Chemical shifts are expressed in d
units relative to tetramethylsilane (TMS) signal as internal reference in

.
AlCl 6H O/KI/CH CN/H O
1261
2
3
2
.
Table 1. Cleavage of C–O bonds and formation of halides using AlCl
CH CN/H O system
3
6H
2
O/KI/
3
2
Time
(h)
Yield
(%)
a,b,c,d
Product
Sl. No.
Substrate
1
2
3
4
CH
2
(COOEt)
2
17
13
14
9
65
75
65
80
CH
2 2
(COOH)
Ph–COOEt
Ph–COOH
Ph–CH 55 CH–COO-Me
Ph–CH 55 CH–COOH
Ph–OH þ Ph–COOH
Ph–O–CO–Ph
7
8
5
6
Ph–OCOMe
4
92
90
Ph–OH
10
7
8
5
4
95
80
9
4
4
85
83
10
1
1
1
2
12
5
76
89
9
0
1
3
4
6
6
85
89
1
(
continued)

1
262
P. Gogoi et al.
Table 1. Continued
Time
(h)
Yield
(%)
a,b,c,d
Sl. No.
Substrate
Product
1
5
6
90
1
1
6
7
6
6
84
90
1
8
6
77
19
20
21
22
C
6
H
5
–CH
2
–OH
p-HO-C H –CH –OH
3
3
3
4
91
90
92
88
C
p-HO–C H –CH –I
6
H
5
–CH
2
–I
6
4
2
6
4
2
p-MeO–C
6
H
4
–CH –OH
–OH
2
p-MeO–C
p-Cl–C
6
H
4
–CH
2
–I
p-Cl–C
6
H
4
–CH
2
6
H
4
–CH –I
2
a
b
c
Isolated yield.
The ratio of water and acetonitrile 1:10.
Melting points were compared with authentic samples.
d
All the compounds gave satisfactory IR, NMR, and elemental analyses.
.
Table 2. Oxidation of alcohols to aldehydes and ketones using AlCl
CH
3
6H
2
O/KI/
3
CN/H
2
O in the presence of DMSO
a,b,c,d
Sl. No.
Substrate
Time (h) Yield (%)
Product
1
2
3
C H –CH –OH
6
5
5
70
69
65
C H –CHO
6 5
5
2
p-NO –C H –CH –OH
2
p-NO –C H –CHO
2 6 4
6
4
2
5.5
4
5
CH O–C H –CH OH
3
4
7
71
54
CH O–C H –CHO
3 6 4
6
4
2
a
Isolated yield.
b
The ratio of water and acetonitrile 1:10.
Mp and bp were compared with authentic samples.
c
d
All the compounds gave satisfactory IR, NMR, mass, and elemental analyses.

.
AlCl 6H O/KI/CH CN/H O
1263
2
3
2
Scheme 1.
CDCl . FTIR spectra were recorded in CHCl or on KBr pellets. Commer-
3
3
.
cially available AlCl 6H O and potassium iodide (KI) were used directly.
3
2
Column chromatography was performed on silica gel (60–120 mesh) using
ethyl acetate and hexane as eluent.
General Procedure for Chemoselective C–O Bond Cleavage
.
AlCl3 6H O (0.240 g, 1 mmol) and KI (0.249 g, 1.5 mmol) were stirred in
2
acetonitrile and water (15 ml, 10:1) at room temperature for 30 min, and
ester (1 mmol) was added to it. The reaction mixture was refluxed at 80 8C
for the stipulated time (Table 1), and the progress of the reaction was
monitored by TLC. The solvent was distilled under reduced pressure, and
the residue was diluted with water (25 ml) and extracted with DCM. The
organic layer was washed with 5% sodium thiosulphate solution (25 ml) and
with water (2 ꢀ 50 ml) and dried over anhydrous sodium sulphate. The
solvent was evaporated and after preparative TLC gave the desired product.
General Procedure for Oxidation of Alcohols
.
AlCl 6H O (0.240 g, 1 mmol) and KI (0.249 g, 1.5 mmol) were stirred in
3
2
acetonitrile and water (15 ml, 10:1) at room temperature for 30 min. To this
mixture, alcohol (1 mmol) and DMSO (390 mg, 5 mmol) were added and
refluxed at 80 8C under nitrogen for the stipulated time (Table 1, entries
2
3–26). The solvent was distilled off to half of its volume under reduced
pressure and poured into water (2 ꢀ 100 ml) and extracted with diethyl
ether (2 ꢀ 25 ml). The organic layer was washed with 5% sodium thiosulphate
solution (20 ml) and then with water (4 ꢀ 50 ml) and dried over anhydrous
Na SO . The residue was purified by preparative TLC to get analytically
2
4
pure aldehyde/ketones. All the products were commercially available and
identified by comparison of the isolated products with authentic samples.

1
264
P. Gogoi et al.
ACKNOWLEDGMENT
The authors acknowledge the director and the Analytical Division of this
laboratory for their kind help. Also, P. G. and S. D. S. are grateful to
Council of Scientific & Industrial Research (CSIR), New Delhi, for its grant
of Junior Research Fellow (JRF) fellowships.
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