Silica gel-mediated hydrohalogenation of unactivated alkenes using hydrohalogenic acids under organic solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2018.10.043

Silica gel-mediated hydrochlorination of unactivated alkenes using 35% hydrochloric acid under organic solvent-free conditions proceeded to give the corresponding chlorides in good yields. Hydrobromination or hydriodination using 47% hydrobromic acid or 55% hydriodic acid afforded the corresponding halides, respectively. Silica gel could be recycled five times without any significant loss of activities.

Full text of DOI:10.1016/j.tetlet.2018.10.043

Accepted Manuscript
Silica gel-mediated hydrohalogenation of unactivated alkenes using hydroha-
logenic acids under organic solvent-free conditions
Kiyoshi Tanemura
PII:
S0040-4039(18)31262-0
https://doi.org/10.1016/j.tetlet.2018.10.043
TETL 50353
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
6 September 2018
14 October 2018
22 October 2018
Please cite this article as: Tanemura, K., Silica gel-mediated hydrohalogenation of unactivated alkenes using
hydrohalogenic acids under organic solvent-free conditions, Tetrahedron Letters (2018), doi: https://doi.org/
10.1016/j.tetlet.2018.10.043
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Silica gel-mediated hydrohalogenation of
unactivated alkenes using hydrohalogenic
acids under organic solvent-free conditions
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Kiyoshi Tanemura
H
C
R1
R2
R3
R4
R1
R2
R3
R4
Aqueous HX
SiO2
C
C
C
X
HX = HCl, HBr, HI
Solventless !

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Silica gel-mediated hydrohalogenation of unactivated alkenes using hydrohalogenic
acids under organic solvent-free conditions
Kiyoshi Tanemura 
a Chemical Laboratory, School of Life Dentistry at Niigata, Nippon Dental University, Hamaura-cho, Niigata 951-8580, Japan
———
ARTICLE INFO
ABSTRACT
 Corresponding author. Fax: +81 25 267 1134; E-mail address: tanemura@ngt.ndu.ac.jp (K. Tanemura).
Article history:
Received
Silica gel-mediated hydrochlorination of unactivated alkenes using 35% hydrochloric acid under
organic solvent-free conditions proceeded to give the corresponding chlorides in good yields.
Received in revised form
Accepted
Available online
Hydrobromination or hydriodination using 47% hydrobromic acid or 55% hydriodic acid
afforded the corresponding halides, respectively. Silica gel could be recycled five times without
any significant loss of activities.
2009 Elsevier Ltd. All rights reserved.
Keywords:
Silica gel
Alkenes
Solvent-free conditions
Addition
Hydrochloric acid
Hydrogen chloride
Addition of hydrogen halides to alkenes is one of the classic
reactions in organic chemistry.1,2 Hydrochlorination of
unactivated alkenes except strained alkenes or styrene derivatives
is slow and still challenging.3-6 Hydrobromination7 of alkenes
competes with radical anti-Markovnikov addition. Furthermore,
generation of gaseous hydrogen halides requires complex
instruments and inconvenient procedures. Kropp et al.8-10 have
devised greatly convenient procedure which uses the hydrolysis
of active halides such as (COCl)2, SOCl2, Me3SiBr, and PI3 in the
presence of silica gel or alumina in CH2Cl2.11,12 In the cases of
(COCl)2 and SOCl2, highly toxic CO and SO2 evolve,
respectively. If the most convenient and widely available
hydrohalogenic acids can be employed, it is great advantage from
atom economical and environmental points of view.
Hydrohalogenation of alkenes using hydrohalogenic acids in the
presence of catalytic amounts of hexadecyltributylphosphonium
bromide has been reported.13 Recently, the use of a solution of
HBr in dioxane14 and HCl/N,N'-dimethylpropyleneurea (DMPU)-
acetic acid catalytic system15 were devised.
adsorbing water of hydrohalogenic acids using silica gel. In this
paper, we wish to report the silica gel-mediated
hydrohalogenation of alkenes involving unactivated ones using
commercially available hydrohalogenic acids.
First, we examined the reactions of 1-decene (1a) with 35%
hydrochloric acid at room temperature for 24 h in the presence of
silica gel. The results are shown in Table 1. When 8.0 mmol of
35% hydrochloric acid and 5 g of Silica gel 60 (63-200 μm,
Merck) were used, compound 1a (2.0 mmol) was completely
consumed to give 2-chlorodecane (2a) in 88% yield (entry 1).
The use of the other silica gel such as Silica gel 60 (63-200 μm,
Aldrich), Silica gel 60 (40-75 μm, Aldrich), Wakogel C-200 (75-
150 μm, Wako), and Silica gel 60 (63-200 μm, Nakalai) afforded
the similar results (entries 7-9 and 11). When spherical silica gel
such as Wakosil C-200 (64-210 μm, spherical, Wako), Silica gel
60 (63-200 μm, spherical, Nakalai), Silica gel 60 (45-106 μm,
spherical, Nakalai), and Silica gel 60 (63-210 μm, spherical,
Kanto) were used, mixing is easier than crushed type (entries 10
and 12-14). No reaction occurred in the cases of acidic, neutral,
and basic alumina (entries 15-17). In these reactions, hydrogen
chloride was completely consumed by the salt formation with
alumina.35 When acidic alumina was employed, AlCl3∙6H2O was
obtained from aqueous filtrate in 90% yield based on hydrogen
chloride, which was identified by comparison of the IR spectrum
with that of the commercially available sample. In addition,
detection of an aluminum ion was conducted by the aluminon
colorimetric methods. Detection of a chloride ion was carried out
by the silver nitrate colorimetric method. In the cases of basic
and neutral alumina, hydrogen chloride would be further
consumed by neutralization with alumina.36 In the absence of
silica gel, hydrochlorination did not occur at all with and without
the solvents (entries 18-20).
Silica gel16,17 or alumina18-21 is known to be an excellent
medium which sometimes works as a mild acidic or basic
catalyst for some organic transformations under solvent-free
conditions.22-29 It is easily separated from the products after the
reactions by filtration. In addition, it is useful from the
environmental point of view because the procedure does not
require harmful organic solvents as reaction media. The use of
silica gel or alumina as the medium has been applied for Friedel-
Crafts-type nitration of arenes,22 allylation of aldehydes with
tetraallyltin,30 Horner-Wadsworth-Emons reactions,31 and
nitroaldol reactions.20
During the course of our investigations on the activation of
organic reactions by silica gel32 and halogenation of organic
compounds,33,34 we planned to produce hydrogen halides by

2
Tetrahedron
3
4
8
8
8
8
8
8
8
8
8
SiO2 (5)
SiO2 (4)
SiO2 (2)
SiO2d (5)
Al2O3e (5)
Al2O3f (5)
Al2O3g (5)
-
81
96
57
100
0
72
86
50
86
0
Table 1
Hydrochlorination of 1a using hydrochloric acida
Entry
4
35% HCl (mmol) Adsorbent (g)
Conv.(%)b
Yield (%)c
5
1
8
6
4
8
8
4
8
8
8
8
8
8
8
8
8
8
8
8
8
8
SiO2 (5)
SiO2 (5)
SiO2 (5)
SiO2 (4)
SiO2 (2)
SiO2 (2)
SiO2d (5)
SiO2e (5)
SiO2f (5)
SiO2g (5)
SiO2h (5)
SiO2i (5)
SiO2j (5)
SiO2k (5)
Al2O3l (5)
Al2O3m (5)
Al2O3n (5)
-
100
86
81
90
70
73
100
90
96
94
91
100
100
100
0
88
75
70
77
62
58
89
82
89
85
84
86
90
90
0
6
2
7
3
8
0
0
4
9
0
0
5
10
11h
12i
0
0
6
-
0
0
7
-
0
0
8
a Alkene 1a (2.0 mmol), silica gel 60 (63-200 μm, Merck), room temp, 24 h.
b Determined by 1H NMR spectroscopy based on alkene 1a.
c Isolated yields of 3a.
9
10
11
12
13
14
15
16
17
18
19o
20p
d Silica gel 60 (63-200 μm, spherical, Nacalai) was used.
e Acidic alumina was used.
f Neutral alumina was used.
g Basic alumina was used.
h CH2Cl2 (5 mL) was added.
i MeCN (5 mL) was added.
Table 3
Hydriodination of 1a using hydriodic acida
0
0
Entry 55% HI (mmol)
Adsorbent (g) Conv.(%)b
Yield (%)c
0
0
1
8
SiO2 (5)
SiO2 (5)
SiO2 (5)
SiO2 (5)
SiO2 (3)
SiO2e (5)
Al2O3f (5)
Al2O3g (5)
Al2O3h (5)
-
100
100
97
73
94
100
0
91
90
83
64
85
89
0
0
0
2
5
3d
4d
5d
6
4
-
0
0
-
0
0
2.4
5
a Alkene 1a (2.0 mmol), silica gel 60 (63-200 μm, Merck), room temp, 24 h.
b Determined by 1H NMR spectroscopy based on alkene 1a.
c Isolated yields of 2a.
5
d Silica gel 60 (63-200 μm, Aldrich) was used.
e Silica gel 60 (40-75 μm, Aldrich) was used.
f Wakogel C-200 (75-150 μm, Wako) was used.
g Wakosil C-200 (64-210 μm, spherical, Wako) was used.
h Silica gel 60 (63-200 μm, Nacalai) was used.
i Silica gel 60 (63-200 μm, spherical, Nacalai) was used.
j Silica gel 60 (45-106 μm, spherical, Nacalai) was used.
k Silica gel 60 (63-210 μm, spherical, Kanto) was used.
l Acidic alumina was used.
7
5
8
5
0
0
9
5
0
0
10
11i
12j
5
0
0
5
-
0
0
5
-
0
0
m Neutral alumina was used.
n Basic alumina was used.
a Alkene 1a (2.0 mmol), silica gel 60 (63-200 μm, Merck), room temp, 8 h.
b Determined by 1H NMR spectroscopy based on alkene 1a.
c Isolated yields of 4a.
o CH2Cl2 (5 mL) was added.
p MeCN (5 mL) was added.
d Time 24 h.
e Silica gel 60 (63-200 μm, spherical, Nacalai) was used.
f Acidic alumina was used.
The results for hydrobromination and hydriodination of 1a
were summarized in Tables 2 and 3. When 8.0 mmol of 47%
hydrobromic acid and 5 g of silica gel were employed, the
reaction of 1a (2.0 mmol) proceeded completely to give 2-
bromodecane (3a) in 88% yield (Table 2, entry 1). On the other
hand, the use of 5.0 mmol of 55% hydriodic acid and 5 g of silica
gel was sufficient for complete conversion of 1a (2.0 mmol)
(Table 3, entry 2). When spherical silica gel was employed,
mixing was easier compared with crushed one (Table 2, entry 6
and Table 3, entry 6).
g Neutral alumina was used.
h Basic alumina was used.
i CH2Cl2 (5 mL) was added.
j MeCN (5 mL) was added.
We examined hydrochlorination of various alkenes with 35%
hydrochloric acid at room temperature in the presence of Silica
gel 60 (63-200 μm, spherical, Nakalai). The results are
summarized in Table 4. Terminal, internal, cyclic, and
trisubstituted alkenes 1a-k and styrene 1l4,37 were converted into
the corresponding chlorides 2a-l in good yields according to
Markovnikov’s rule (entries 1-12). anti-Markovnikov products
were not detected in all cases. The internal alkenes reacted more
slowly than the corresponding terminal ones (compare 1a and 1f,
1b and 1g). From the reaction of Δ9,10-octaline (1m), we obtained
trans-decalin (2m)6,38-40 in 87% yield together with small
amounts of several unidentified compounds (entry 13). Although
we tried separation of the products using GC/MS, it failed
because of the decomposition during the analysis.
Table 2
Hydrobromination of 1a using hydrobromic acida
Entry 47% HBr (mmol) Adsorbent (g) Conv.(%)b
Yield (%)c
1
2
8
6
SiO2 (5)
SiO2 (5)
100
91
88
80

3
Stereochemistry of 2m was determined by the comparison of the
IR spectra in CS2 with that reported in the literature.39
Table 4
Silica-gel mediated hydrochlorination of alkenesa
Scheme 1. Selective hydrochlorination of 1n.
Entry
Yield (%)c
Conv.(%)b
Substrate
Time (h)
Product
The results for hydrobromination of various alkenes were
shown in Table 5. Bromides 3a, 3b, 3f-j, and 3l were formed in
good yields from the corresponding terminal, internal, cyclic, and
trisubstituted alkenes 1a, 1b, and 1f-j, and styrene 1l at room
temperature in the presence of Silica gel 60 (63-200 μm,
spherical, Nakalai) according to Markovnikov’s rule (entries 1-7).
anti-Markovnikov products were not observed in all cases. The
reactions of the internal alkenes were slower than the
corresponding terminal ones (compare 1a and 1f, 1b and 1g). In
the reaction of 1k, the yield of 3k decreased (65%) because of the
hydrolysis of 3k to 2-benzyl-2-propanol during the reaction
(entry 8).
24
1
100
88
92
1a
2a
Cl
48
2
100
1b
2b Cl
Cl
3
4
96
97
88
93
80
Ph
1c
2c
Ph
F
288
1d
Cl
F
2d
144
5
100
90
1e
Cl
Table 5
MeO
2e
2f
MeO
Silica-gel mediated hydrobromination of alkenesa
6
7
48
72
85
99
82
88
Conv.(%)b
Time (h)
Product
Yield (%)c
86
Entry
Substrate
1f
Cl
Cl
1
2
24
100
1g
2g
1a
3a
Br
Cl
2h
48
48
48
8
9
100
93
97
92
1h
1i
3b Br
1b
3
4
48
72
90
97
88
94
100
98d
Cl
3f
1f
2i
Br
Br
Cl
10
48
3
100
100
91
93
3g
1g
1j
2j
Br
5
6
48
48
93
80
1h
Cl
H
Me
Me
3h
11
12
13
a
C
C
Ph CH2
C
Me
Ph
98d
100
1k
2k
Me
Br
1i
3i
Cl
Ph
15
48
Br
100
100
88
1l
7
Ph
2l
48
100
100
100
84
1j
3j
Br
H
87e
H
Me
Me
65d,e
1.5
1
8
9
C
C
Ph CH2
C
Me
1m
2m
Cl
Ph
3k
1k
Me
Alkene 1 (2.0 mmol), 35% hydrochloric acid (8.0 mmol), silica gel 60 (63-
200 μm, spherical, Nacalai, 5.0 g), room temp.
Br
80
Ph
1l
3l
b Determined by 1H NMR spectroscopy based on alkene 1.
c Isolated yields.
Ph
d Yield was determined by 1H NMR with CH2Cl2 as the internal standard.
e Small amounts of several unidentified compounds were produced.
a
Alkene 1 (2.0 mmol), 47% hydrobromic acid (8.0 mmol), silica gel 60 (63-
200 μm, spherical, Nacalai, 5.0 g), room temp.
b Determined by 1H NMR spectroscopy based on alkene 1.
c Isolated yields.
Chemoselectivity and regioselectivity were examined using
(R)-carvone (1n) (Scheme 1). Hydrochlorination of 1n proceeded
at room temperature for 45 min according to Markovnikov’s rule
to give 2n (83%) and carvacrol (5) (11%) without the addition to
the enone moiety.6 After 24 h, the yield of compound 5 increased
up to 44% by acid-catalyzed isomerization41 of 2n.
d Yield was determined by 1H NMR with CH2Cl2 as the internal standard.
e 2-Benzyl-2-propanol was obtained in 32% yield.
As seen in Table 6, the corresponding iodides were obtained
in good yields by the reactions of terminal, internal, cyclic
alkenes 1a, 1b, and 1f-h and styrene 1l at room temperature in
the presence of Silica gel 60 (63-200 μm, spherical, Nakalai)
according to Markovnikov’s rule (entries 1-5 and 9). The internal
alkenes reacted more slowly than the corresponding terminal
ones (compare 1a and 1f, 1b and 1g). Complex mixture was
obtained in the hydriodination of trisubstituted alkenes 1i and 1j
because of the instability of iodides 4i and 4j (entries 6 and 7).
O
O
OH
HCl
+
SiO2
RT
Cl
H
H
1n
2n
5
45 min
24 h
83%
52%
11%
44%

4
Tetrahedron
The reaction of 1k afforded not only iodide 4k (63%) but also
without any significant loss of activities for the synthesis of
chloride 2a, bromide 3a, and iodide 4a.
2-benzyl-2-propanol (32%) (entry 8). Addition of hydrogen
iodide42 proceeded faster than those of hydrogen chloride and
hydrogen bromide.
In conclusion, we devised the silica gel-mediated
hydrohalogenation of alkenes using hydrohalogenic acids.43
Widely available hydrohalogenic acids can be employed.
Furthermore, the procedure is environmentary benign since the
reactions can be conducted without harmful organic solvents.
Silica gel could be recycled without loss of activities. Silica gel
acts as a dehydration agent of hydrohalogenic acids to produce
hydrogen halides as well as an efficient dispersant to prevent
viscous properties under neat conditions.
Table 6
Silica-gel mediated hydriodination of alkenesa
Entry
1
Conv.(%)b
Substrate
Product
Time (h)
Yield (%)c
93
8
100
1a
4a
I
References and notes
2
3
4
24
100
96
4b
I
1b
1. Hassner, A.; Fibiger, R. F. Synthesis 1984, 960-960.
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48
87
99
100
100
4f
1f
I
4g
I
1g
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I
5
6
7
100
100
89
24
24
24
1h
4h
d
-
I
1i
4i
I
d
100
100
-
1j
4j
I
H
Me
Me
8
9
0.75
4
63e,f
91
Ph CH2
C
Me
C
C
Ph
4k
Me
1k
I
100
1l
Ph
4l
Ph
a Alkene 1 (2.0 mmol), 55% hydriodic acid (5.0 mmol), silica gel 60 (63-200
μm, spherical, Nacalai, 5.0 g), room temp.
b Determined by 1H NMR spectroscopy based on alkene 1.
c Isolated yields.
d Complex mixture was obtained.
16. Serra-Muns, A.; Guérinot, A.; Reymond, S.; Cossy, J. Chem.
Commun. 2010, 46, 4178-4180.
e Yield was determined by 1H NMR with CH2Cl2 as the internal standard.
f 2-Benzyl-2-propanol was obtained in 36% yield.
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Table 7
Recycle experiments for the hydrohalogenation of 1a
Yield (%)a
Entry
1st
86
86
89
2nd
84
3rd
84
86
86
4th
89
89
90
5th
90
85
87
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1b
2c
3d
88
89
a Isolated yields.
b Alkene 1a (2.0 mmol), 35% hydrochloric acid (8.0 mmol), silica gel 60 (63-
200 μm, spherical, Nacalai, 5.0 g), room temp, 24 h.
c Alkene 1a (2.0 mmol), 47% hydrobromic acid (8.0 mmol), silica gel 60 (63-
200 μm, spherical, Nacalai, 5.0 g), room temp, 24 h.
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The procedure was scaled up 20-fold for the syntheses of
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yields, respectively.
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Recycle experiments for the addition of hydrogen halides to
1a are shown in Table 7. Silica gel could be recycled five times

5
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material
was
obtained.
The
hydrochlorination,
hydrobromination, and hydriodination of 1k and 1l were slower
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Acknowledgments
We thank Center for Coordination of Research Facilities,
Institute for Research Promotion, Niigata University for NMR
measurements and high resolution mass analysis. We thank
Hitachi Chemical Techno Service Co., Ltd for NMR
measurements and GC/MS analysis. We thank the Research
Promotion Grant (NDU Grants N-18013) from Nippon Dental
University.
Supplementary data
41. Singh, B.; Patial, J.; Sharma, P.; Chandra, S.; Kaul, P.; Maity, S.
Indian J. Chem. Technol. 2011, 18, 21-28.
Supplementary data associated with this article can be found,
in the online version.
42. Barluenga, J.; González, J. M.; Campos, P. J.; Asensio, G.
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43 We tested the hydrohalogenation of trisubstituted alkenes (1i and
1j) and styrene derivatives (1k and 1l) without silica gel. The
hydrochlorination and hydrobromination of compounds 1i and 1j
proceeded at the similar rates with those mediated by silica gel.
In the cases of the hydriodination of 1i and 1j, only polymeric
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* Silica gel-mediated hydrohalogenation of alkenes
was developed.
* Widely available hydrohalogenic acids can be
employed.
* Reactions proceeded under organic solvent-free
conditions.
* Silica gel can be recycled without significant loss
of activities.