Sodium bisulfite: An efficient catalyst for ether formation via dehydration of aromatic/aliphatic alcohol

Article abstract of DOI:10.1002/cjoc.201190220

Straightforward etherification of benzyl alcohols (1) via intermolecular dehydration can be efficiently catalyzed by sodium bisulfite under solvent-free conditions. In the presence of 0.3 mol% or 0.6 mol% amount of sodium bisulfite, symmetric and unsymmetric ethers are prepared from the corresponding alcohols in high yields (up to 95%). Etherification of benzhydryl alcohols is also discussed. Copyright

Full text of DOI:10.1002/cjoc.201190220

FULL PAPER
Sodium Bisulfite: An Efficient Catalyst for Ether Formation via
Dehydration of Aromatic/Aliphatic Alcohol
Wang, Hui*,a(王辉)
Zhu, Xingfeia(朱兴飞)
Lu, Yangningb(陆洋宁)
Li, Yuea(李悦)
Gao, Xianga(高翔)
a Chemistry Department, Fudan University, Shanghai 200433, China
b School of Life Sciences, Fudan University, Shanghai 200433, China
Straightforward etherification of benzyl alcohols (1) via intermolecular dehydration can be efficiently catalyzed
by sodium bisulfite under solvent-free conditions. In the presence of 0.3 mol% or 0.6 mol% amount of sodium bi-
sulfite, symmetric and unsymmetric ethers are prepared from the corresponding alcohols in high yields (up to 95%).
Etherification of benzhydryl alcohols is also discussed.
Keywords sodium bisulfite, etherification, dehydration, aromatic alcohol, aliphatic alcohol
Introduction
NaHSO3 at 110 ℃ to give a symmetrical ether 3a in up
to 90% yield (Table 1, Entry 3). A decrease in tempera-
ture led to an incomplete reaction, while an increase in
temperature produced a relatively large amount of in-
tramolecular dehydration product 3a' (Table 1, Entries 4
and 5).
Preparation of ethers is one of the most fundamen-
tal reactions in synthetic organic chemistry. One of the
most common methods for synthesis of ethers, Wil-
liamson ether synthesis, requires initial transformation
of alcohols to halides or tosylates.1 Direct dehydration
of alcohols promoted by acids,2 metal complexes,3 di-
methyl sulfoxide,4 iodine,5 Y-zeolite,6 or ionic liquid7
provides a straightforward method for the preparation of
ethers. For example, Das et al.8 reported that sil-
ica-supported sodium hydrogen sulfate (NaHSO4•SiO2)
can catalyze the transformation of p-hydroxybenzyl al-
cohols to p-hydroxybenzyl ethers. Aslam et al.9 reported
synthesis of a bisarylalkyl ether using a sub-
stoichiometric amount of potassium bisulfate (KHSO4)
as a catalyst. However, strong acidity of NaHSO4 and
KHSO4 (pKa 1.92) often leads to undesired side-
reactions during etherification of alcohols.
Scheme 1
Table 1 Etherification of 1a catalyzed with sodium bisulfite
under various conditions
As the cheap sodium bisulfite (NaHSO3) is a weaker
acid (pKa 7.21) when compared with NaHSO4 and
KHSO4, we decided to investigate its reactivity as a
catalyst in etherification of alcohols.10 Herein, we would
like to report the NaHSO3 catalyzed direct etherification
of aromatic/aliphatic alcohols, as well as benzhydryl
alcohols.11
Temp./
Entry Catalyst amount
Time Yielda (3a)Yielda (3a')
℃
1
2
3
4
5
0.6 mol%
0.3 mol%
0.3 mol%
0.3 mol%
0.3 mol%
110 1 h
110 10 min
110 1 h
100 1 h
150 1 h
88%
5%
4%
—
90%
18%
79%
3%
17%
16%
Results and discussion
a NMR yields.
First,
a
straightforward etherification of
Under the optimized reaction conditions, straight-
forward etherifications of benzyl alcohols possessing
β-hydrogens were carried out (Scheme 2 and Table 2). It
was found that etherifications of 1 proceeded smoothly
phenylethyl alcohol 1a was carried out using NaHSO3
as a catalyst under various reaction conditions (Scheme
1 and Table 1). It was found that 1a could undergo in-
termolecular dehydration with 0.3 mol% amount of
*
E-mail: wanghui@fudan.edu.cn; Tel.: 0086-021-65642796; Fax: 0086-021-65643819
Received September 20, 2010; revised December 31, 2010; accepted January 20, 2011.
Project supported by the Scientific Research Foundation of the Education Ministry for Returned Chinese Scholars and the Fudan University Youth
Scientific Foundation.
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Chin. J. Chem. 2011, 29, 1180— 1184

Sodium Bisulfite: An Efficient Catalyst for Ether Formation
Table 2 Dehydration of arylalkyl alcohols 1a— 1e and 1c with alkyl alcohol 2a—2c catalyzed with sodium bisulfite under solvent-free
conditions
Entry
R1OH
R2OH
Product
Yielda/% (3) Yielda/% (3')
1
90 (88)b
3
2c
4
94b
3
92 (89)b
95 (90)b
36b
4
4
5
5d
19
6
7
8
95 (92)b
88 (79)
84 (80)
4
-
CH3(CH2)2CH2OH
16
2a
CH3(CH2)5CH2OH
9
90 (85)
10
2b
10
91 (83)
9
a NMR yields. Isolated yields are given in the parentheses. b The product is about 1∶1 mixtures of dl enantiomers and meso compounds.
c NaHSO4 (0.6 mol%) was used as a catalyst. d KHSO4 (0.6 mol%) was used as a catalyst.
Chin. J. Chem. 2011, 29, 1180— 1184
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Wang et al.
FULL PAPER
Scheme 2
Table 3 Dehydration of benzhydryl alcohols 4a— 4e catalyzed
with sodium bisulfite under solvent-free conditions
Entry
Ar1
Ar2
Product
Yielda,b/%
1
4a
5a
92 (90)
under solvent-free conditions to afford the correspond-
ing symmetric bisarylalkyl ethers 3 in high yields. For
example, etherification of alcohol 1b with 0.3 mol%
amount of NaHSO3 as a catalyst leads to the desired
symmetric ether 3b in up to 92% yield with a small
amount of intramolecular dehydration by-product sty-
rene 3b' (Table 2, Entry 3). The same selectivity was
also observed in the case of 1a, 1c and 1d which bear
electron-donating or withdrawing substituents on the
aromatic ring (Table 2, Entries 1, 4 and 6). Interestingly
when NaHSO4 was applied as a catalyst for etherifica-
tion of alcohol 1a, styrene 3a' was obtained in 94%
yield, and ether 3a was only in 4% yield (Table 2, Entry
2). And KHSO4 gave similar results when it was applied
as a catalyst for etherification of alcohol 1c (Table 2,
Entry 5).9 These results suggested that NaHSO3 showed
a unique property for direct etherification of benzyl al-
cohols possessing β-hydrogens. It is also noteworthy
that dehydration of piperonyl alcohol (1e) with NaHSO3
as a catalyst provided the corresponding symmetric
ether 3e (Table 2, Entry 7), while polymerization of 1e
was observed in the case of NaHSO4. Such opposite
reaction selectivity could possibly due to the relative
weaker acidity of NaHSO3 compared with NaHSO4/
KHSO4.12,13
2
3
4
5
4b
4c
4d
4e
5b
5c
5d
5e
99 (95)
95 (92)
96 (95)
95 (94)
a NMR yields. Isolated yields are given in the parentheses. All
products were about 1∶1 mixtures of dl enantiomers and meso
compounds.
b
the aromatic ring have little effect on the reaction rate.
Experimental
General
NaHSO3, NaHSO4, KHSO4 and aliphatic alcohols
were purchased from commercial source and were used
as received. Benzyl alcohols and benzhydryl alcohols
were obtained by reduction of aromatic ketones with
NaBH4 in MeOH. 1H NMR spectra were measured on a
JEOL 400 MHz spectrometer with TMS as an internal
standard in CDCl3. 13C NMR spectra were measured on
a Bruker 500 MHz spectrometer with TMS as an inter-
nal standard in CDCl3. High-resolution mass spectra
(HRMS) were obtained on a Bruker microTOF II.
Subsequently we investigated direct etherifications
of 1 with aliphatic alcohols catalyzed with NaHSO3. To
our delight, we found that 1c and primary aliphatic al-
cohol 2a, 2b or 2c underwent efficient etherification to
afford unsymmetrical ether 3f, 3g or 3h in good yields
and high selectivities (Table 2, Entries 8, 9 and 10). For
instance, 1c reacted with 4.0 equiv. of 3-methyl-1-
butanol (2c) catalyzed by NaHSO3 at 110 ℃ to give 3h
in 95% yield, without formation of 3c or 3c'.
General procedure for compounds 3a— 3e
A mixture of 1-phenylethanol (1a) (244 mg, 2.0
mmol) and NaHSO3 (0.6 mg, 0.006 mmol) was stirred
at 110 ℃ in oil bath for 1 h. After the reaction finished,
the residue was purified by column chromatography on
silica gel to give the corresponding ether 3a in 88% iso-
lated yield.
To extend the scope of this methodology, NaHSO3
was also applied to catalyze etherification of various
benzhydrol derivatives (Scheme 3 and Table 3). Both
activated and deactivated benzhydryl alcohols demon-
strated good reactivities. For example, the symmetrical
ether 5b can be efficiently synthesized from
(4-methoxyphenyl)(phenyl)methanol (4b) in the pres-
ence of a catalytic amount of NaHSO3. In the absence of
NaHSO3, we observed no etherification reaction.14 In-
terestingly, bis(4-fluorophenyl)methanol (4d) can also
smoothly undergo dehydration to afford ether 5d in a
similar yield as 4b, which suggests that substituents on
1-(1-(1-Phenylethoxy)ethyl)benzene (3a)2j Col-
1
orless oil, 88% yield; H NMR (CDCl3, 400 MHz) δ:
1.38 (d, J＝6.4 Hz, 6H), 4.24 (q, J＝6.4 Hz, 2H),
7.32—7.40 (m, 10H).
1-Methyl-4-(1-(1-p-tolylethoxy)ethyl)benzene (3b)2j
Colorless oil, 89% yield; 1H NMR (CDCl3, 400 MHz) δ:
1.36 (d, J＝6.0 Hz, 6H), 2.36 (s, 6H), 4.21 (q, J＝6.4
Hz, 2H), 7.09—7.23 (m, 8H).
Scheme 3
1-Methoxy-4-(1-(1-(4-methoxyphenyl)ethoxy)-
ethyl)benzene (3c)2j Colorless oil, 90% yield; 1H
NMR (CDCl3, 400 MHz) δ: 1.35 (d, J＝6.4 Hz, 6H),
3.78 (s, 6H), 4.18 (q, J＝6.8 Hz, 2H), 6.84—6.90 (m,
4H), 7.18—7.25 (m, 4H).
1-Chloro-4-(1-(1-(4-chlorophenyl)ethoxy)ethyl)-
benzene (3d)2j Colorless oil, 92% yield; H NMR
1
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Chin. J. Chem. 2011, 29, 1180— 1184

Sodium Bisulfite: An Efficient Catalyst for Ether Formation
(CDCl3, 400 MHz) δ: 1.34 (d, J＝6.4 Hz, 6H), 4.17 (q,
J＝6.8 Hz, 2H), 7.16—7.33 (m, 8H).
1-((4-Fluorophenyl)((4-fluorophenyl)(4-methoxy-
phenyl)methoxy)methyl)-4-methoxybenzene (5c)
1
5-(((1,3-Dihydroisobenzofuran-5-yl)methoxy)-
methyl)-1,3-dihydroisobenzofuran (3e) White solid,
Yellow oil, 92% yield; H NMR (CDCl3, 400 MHz) δ:
3.78 (s, 3H), 3.79 (s, 3H), 5.29 (s, 2H), 6.84—6.88 (m,
4H), 6.96—7.02 (m, 4H), 7.20—7.23 (m, 4H), 7.27—
7.31 (m, 4H); 13C NMR (CDCl3, 125 MHz) δ: 54.93,
78.84, 113.78, 113.86, 114.92, 115.02, 115.09, 115.20,
128.49, 128.33, 133.69, 133.97, 138.14, 138.41, 159.02,
159.10, 160.93, 161.00, 162.88, 162.96. HRMS calcd
for [C28H24F2O3Na]＋ 469.1586, found 469.1590.
1
m.p. 40—41 ℃ (Lit.15 41—43 ℃), 79% yield; H
NMR (CDCl3, 400 MHz) δ: 4.42 (s, 4H), 5.94 (s, 4H),
6.76—6.79 (m, 4H), 6.86 (s, 2H).
General procedure for compounds 3f— 3h
A mixture of 1-(4-methoxyphenyl)ethanol (1c) (310
mg, 2.0 mmol), 1-butanol (590 mg, 8.0 mmol) and Na-
HSO3 (0.6 mg, 0.006 mmol) was stirred at 110 ℃ for 1
h. After the reaction finished, the residue was purified
by column chromatography on silica gel to give the
corresponding ether 3f in 80% isolated yield.
(Bis(4-fluorophenyl)methoxy)bis(4-fluorophen-
yl)methane (5d) White solid, m.p. 78—79 ℃, 95%
1
yield; H NMR (CDCl3, 400 MHz) δ: 5.30 (s, 2H),
6.99—7.04 (m, 8H), 7.25—7.28 (m, 8H); 13C NMR
(CDCl3, 125 MHz) δ: 78.88, 115.32, 115.50, 128.70,
128.76, 137.45, 161.25, 163.21. HRMS calcd for
[C28H18F4ONa]＋ 469.1186, found 469.1199.
1-(1-Butoxyethyl)-4-methoxybenzene (3f)2i Col-
1
orless oil, 80% yield; H NMR (CDCl3, 400 MHz) δ:
0.88 (t, J＝7.2 Hz, 3H), 1.35—1.42 (m, 2H), 1.41 (d,
J＝6.4 Hz, 3H), 1.51—1.60 (m, 2H), 3.26 (t, J＝6.8 Hz,
2H), 3.80 (s, 3H), 4.34 (q, J＝6.4 Hz, 1H), 6.88 (d, J＝
8.4 Hz, 2H), 7.23 (d, J＝8.4 Hz, 2H).
1-((4-Chlorophenyl)((4-chlorophenyl)(p-tolyl)-
methoxy)methyl)-4-methylbenzene (5e) Yellow oil,
94% yield; 1H NMR (CDCl3, 400 MHz) δ: 2.32 (s, 3H),
2.33 (s, 3H), 5.29 (s, 2H), 7.12—7.20 (m, 8H), 7.24—
7.27 (m, 8H); 13C NMR (CDCl3, 125 MHz) δ: 21.02,
79.20, 127.00, 127.18, 128.24, 128.38, 128.49, 129.15,
129.23, 132.94, 133.07, 137.27, 137.40, 138.28, 138.53,
140.72, 140.96. HRMS calcd for [C28H24Cl2ONa] ＋
469.1096, found 469.1094.
1-(1-(Heptyloxy)ethyl)-4-methoxybenzene
(3g)
Colorless oil, 85% yield; 1H NMR (CDCl3, 400 MHz) δ:
0.90 (t, J＝6.4 Hz, 3H), 1.27—1.35 (m, 6H), 1.42 (d,
J＝6.4 Hz, 3H), 1.47—1.59 (m, 4H), 3.27 (t, J＝6.4 Hz,
2H), 3.82 (s, 3H), 4.36 (q, J＝6.4 Hz, 1H), 6.89 (d, J＝
8.8 Hz, 2H), 7.26 (d, J＝8.8 Hz, 2H); 13C NMR (CDCl3,
125 MHz) δ: 13.82, 22.40, 23.93, 25.98, 28.95, 29.78,
21.63, 54.67, 68.18, 77.25, 113.41, 126.96, 135.06,
158.65. HRMS calcd for [C16H26O2Na]＋ 273.1825,
found 273.1810.
Conclusions
In conclusion, we have developed a simple and effi-
cient protocol for the synthesis of symmetric and un-
symmetric ethers via direct dehydration of benzyl alco-
hols containing β-hydrogens by applying cheap Na-
HSO3 as a catalyst under solvent-free conditions. The
etherification of benzhydryl alcohols catalyzed with
NaHSO3 is also explored. Further studies on NaHSO3
catalyzing C—C, C—O and C—N bond formations are
ongoing in our laboratory.
1-(1-(Heptyloxy)ethyl)-4-methoxybenzene (3h)
Colorless oil, 83% yield; 1H NMR (CDCl3, 400 MHz) δ:
0.92 (d, J＝6.4 Hz, 6H), 1.41 (d, J＝6.4 Hz, 3H),
1.52—1.57 (m, 1H), 1.64—1.75 (m, 2H), 3.44 (dt, J＝
6.4, 10.8 Hz, 1H), 3.50 (dt, J＝6.0, 10.6 Hz, 1H), 3.80
(s, 3H), 4.32 (q, J＝6.4 Hz, 1H), 6.88 (d, J＝8.4 Hz,
2H), 7.23 (d, J＝8.4 Hz, 2H); 13C NMR (CDCl3, 125
MHz) δ: 22.17, 22.52, 23.90, 24.74, 38.60, 54.66, 66.45,
77.30, 113.41, 127.06, 136.02, 158.59. HRMS calcd for
[C14H22O2Na]＋ 245.1512, found 245.1502.
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