CaS2O8: An efficient reagent for etherification of alcohols under microwave irradiation in solvent-free conditions

Article abstract of DOI:10.1080/10426500601015682

A new facile and efficient one-pot method for the synthesis of ethers by the reaction of alcohols with calcium peroxodisulfate under microwave irradiation is described. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500601015682

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Phosphorus, Sulfur, and Silicon
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CaS O : An Efficient Reagent
2
8
for Etherification of Alcohols
under Microwave Irradiation in
Solvent-Free Conditions
a
a
a
Rashid Badri , Ali Reza Kiasat & Simin Nazari
a
Chemistry Department , Shahid Chamran
University , Ahvaz, Iran
Published online: 30 Jan 2007.
To cite this article: Rashid Badri , Ali Reza Kiasat & Simin Nazari (2007) CaS O :
2
8
An Efficient Reagent for Etherification of Alcohols under Microwave Irradiation in
Solvent-Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements,
82:3, 589-593, DOI: 10.1080/10426500601015682
1
To link to this article: http://dx.doi.org/10.1080/10426500601015682
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Phosphorus, Sulfur, and Silicon, 182:589–593, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601015682
CaS O : An Efficient Reagent for Etherification
2
8
of Alcohols under Microwave Irradiation in
Solvent-Free Conditions
Rashid Badri
Ali Reza Kiasat
Simin Nazari
Chemistry Department, Shahid Chamran University, Ahvaz, Iran
A new facile and efficient one-pot method for the synthesis of ethers by the reaction
of alcohols with calcium peroxodisulfate under microwave irradiation is described.
Keywords Alcohols; calcium peroxodisulfate; microwave irradiation; solvent free; sym-
metrical ethers
Etherification is one of the most frequently used functional-group trans-
1
formations in organic synthesis. The most common method to produce
2
ethers is the Williamson synthesis, which involves the reaction of an
alkyl halide and a basic alkoxide. However, base-labile functionalities
in reactants and competing eliminations in the case of secondary and
tertiary halides restrict its application to a wide range of substrates.
In addition, the dehydration of alcohols, especially primary alcohols, is
3
the common method for the preparation of symmetrical ethers. This
condensation reaction is catalyzed by strong acids such as sulphuric
acid at elevated temperatures. Recently, the application of solid acids
such as ion-exchange resins, zeolites, and aluminum phosphates was
4
−6
reported for the synthesis of symmetrical ethers.
2
8
−
Although the use of the peroxodisulfate anion (S2O ) as a strong
one-electron transfer oxidant for the oxidation of a variety of organic
7
−10
compounds has been under intensive investigations in recent years,
its application for the protection of alcohols as tetrahydropyranyl ethers
1
1
was reported. To the best of our knowledge, no report about the use
Received August 4, 2005; accepted August 16, 2006.
We thank Shahid, Chamran University, Ahvaz, Iran for financial support of this work.
Address correspondence to Rashid Badri, Chemistry Department, Chamran Univer-
sity, College of Sciences, Ahvaz, 6137-4-3169, Iran. E-mail: rashidbadri@yahoo.com
589

5
90
R. Badri et al.
of the peroxodisulfate anion for the conversion of different alcohols to
corresponding ethers has been reported.
In previous articles we reported the use of peroxodisulfate an-
ion as an efficient oxidant for the conversion of alcohols, alkyl ben-
zenes, and certain benzylic substrates to their corresponding carbonyl
1
2−14
compounds.
Here we report a convenient synthesis of various types
of symmetrical ethers from corresponding primary and secondary al-
cohols under microwave irradiation and under solvent-free conditions
using calcium peroxodisulfate (Scheme 1).
SCHEME 1
The starting point was the reagent CaS2O8, which can be conve-
niently prepared from calcium oxide and ammonium peroxodisulfate
in water. This reagent was then mixed with silica gel and an alcohol
and irradiated in a microwave oven for an appropriate time. The ethers
prepared in this investigation and their yields are listed in Table I.
As shown in Table I, various types of alcohols react efficiently with
calcium peroxodisulfate to afford corresponding ethers in good to excel-
lent yields. Primary and secondary benzylic alcohols proved to be more
efficient and gave higher yields than aliphatic and non-benzylic alcohols
(
Table I). Since some heterocyclic alcohols instead of giving ethers were
converted to corresponding carbonyl compounds (Table I), we suspect
that oxidation of alcohols to their carbonyl derivatives might happen
initially followed by the transformation of these carbonyl compounds to
ethers during the reaction course. In order to eliminate the ambiguity of
intermediacy of carbonyl compounds during ether formation, we tried
syntheses under the same reaction conditions and time with a mix-
ture of equimolar amounts of alcohol and its corresponding aldehyde
or ketone. No conversion of the carbonyl compound to the ether was
observed, and the isolated products from the reaction mixture were the
corresponding ether resulting from alcohol and the unreacted carbonyl
compound. This evidence clearly rejects the possible intermediacy of
carbonyl compounds in the conversion of alcohols to ethers.
A plausible mechanism could be as showin in Scheme 2.

Etherification of Alcohols with CaS O
591
2
8
TABLE I Conversion of Alcohols to Symmetrical Ethers by CaS
Under Microwave Irradiation Under Solvent–Free Conditions
2 8
O
Substrate
Product
Time (min)
4
Yielda,b (%)
81
CH OH
(
CH ) O
2 2
2
7
8
95
80
CH O
3
CH OH
(CH O
CH2)2O
2
3
(
CH ) O
2 2
CH OH
2
CH O
3
CH O
3
1
0
85
92
83
O N
2
CH OH
2
8
Br
CH OH
2
6
6
CHOHCH3
CHOHCH3
85
CH3(CH2)6CH2OH
CH3(CH2)5CHOHCH3
(CH3(CH2)6CH2)2O
5
5
5
71
78
91
N
CH OH
2
CH2OH
5
90
O
aYields refer to pure isolated products.
b
Products were characterized by comparison of their physical data, and IR and 1H
NMR spectra with those of authentic samples.
SCHEME 2

5
92
R. Badri et al.
CONCLUSION
The procedure for the synthesis of ethers described in this article has
the advantage of simple reaction conditions, easy work-up, and excel-
lent yields. It provides an attractive alternate method for the prepara-
tion of ethers.
EXPERIMENTAL
General
1H NMR spectra were recorded on a Bruker Advance DPX instrument
(
250 MHz). IR spectra were recorded on a Shimadzu 470 spectropho-
tometer. Melting points were measured on a Mettler FP5 apparatus.
Purity determination of the products and reaction monitoring were ac-
complished by TLC on silica gel polygram SILG/UV254 plates. All yields
refer to isolated products. Reactions were performed in a microwave
oven with a 230V-50 Hz power source, 900 W output, and 2450 MHz
operating frequency.
General Procedure for the Synthesis of CaS O
2
8
To a solution of calcium oxide (1.12 g, 20 mmol) in water (25 mL) in
a round-bottomed flask equipped with a magnetic stirrer was added
ammonium peroxodisulfate (4.5 g, 20 mmol). The reaction mixture was
stirred at an ambient temperature for 2 h, and then neutral silica gel
(
10 g) was added. Stirring was continued for an additional 2 h, after
which the water was removed. The white solid was dried and used for
the synthesis of ethers.
General Procedure for the Synthesis of Ethers
In a 100-mL glass beaker, alcohol (1 mmol), calcium peroxodisufate
(
2 mmol), and 2 drops of water were mixed thoroughly; the mixture
was placed in a microwave oven and irradiated at 30% power level for
an appropriate time (4–10 min). After cooling, chloroform (20–30 mL)
was added, and the mixture was stirred for 45 min and filtered. The
solid material was washed with chloroform (20 mL), the solvent from
the filtrate was evaporated, and the crude product was purified on a
silica gel plate (eluent: CCl4/Et2O 4/1). Pure ethers were obtained in
71–95% yields (Table I).

Etherification of Alcohols with CaS O
593
2
8
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