Treatment of alcohols with tosyl chloride does not always lead to the formation of tosylates

Article abstract of DOI:10.3390/molecules16075665

Treatment of substituted benzyl alcohols with tosyl chloride resulted in the formation of the corresponding chlorides, not the usual tosylates. A series of experiments demonstrated that it was possible to predict whether chlorination or tosylation would occur for substituted benzyl alcohols and pyridine methanols. Treatment of electron withdrawing group-substituted benzyl alcohols with tosyl chloride gave the corresponding chlorides in moderate yields under mild conditions, which provided a simple way to directly prepare chlorides from alcohols.

Full text of DOI:10.3390/molecules16075665

Molecules 2011, 16, 5665-5673; doi:10.3390/molecules16075665
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Treatment of Alcohols with Tosyl Chloride Does Not always
Lead to the Formation of Tosylates
Rui Ding, Yong He, Xiao Wang, Jingli Xu, Yurong Chen, Man Feng and Chuanmin Qi *
Key Laboratory of Radiopharmaceuticals, College of Chemistry, Beijing Normal University, Beijing
100875, China; E-Mails: dingrui@mail.bnu.edu.cn (R.D.); heyong@mail.bnu.edu.cn (Y.H.);
wangxiao@mail.bnu.edu.cn (X.W.); xujingli@mail.bnu.edu.cn (J.X.);
chenyurong@mail.bnu.edu.cn (Y.C.); fengman@mail.bnu.edu.cn (M.F.)
* Author to whom correspondence should be addressed; E-Mail: qicmin@sohu.com;
Tel.: +86-136-8138-0097; Fax: +86-010-5880-2075.
Received: 5 April 2011 / Accepted: 13 June 2011 / Published: 1 July 2011
Abstract: Treatment of substituted benzyl alcohols with tosyl chloride resulted in the
formation of the corresponding chlorides, not the usual tosylates. A series of experiments
demonstrated that it was possible to predict whether chlorination or tosylation would occur
for substituted benzyl alcohols and pyridine methanols. Treatment of electron withdrawing
group-substituted benzyl alcohols with tosyl chloride gave the corresponding chlorides in
moderate yields under mild conditions, which provided a simple way to directly prepare
chlorides from alcohols.
Keywords: tosyl chloride; chlorination; tosylation; benzyl alcohols; pyridine methanols
1. Introduction
Alkyl tosylates are versatile substrates for substitution reactions. They contain an excellent leaving
group and can be readily prepared from tosyl chloride and an alcohol, allow replacement of the
hydroxy group by many good nucleophiles. Furthermore they are often crystalline solids that can be
isolated and purified before further reaction. Tosylate is often a better leaving group than halide, as its
preparation from an alcohol avoids stereochemical uncertainties and skeletal rearrangements. The
tosylates can then be used in reactions with a variety of nucleophiles to give the corresponding
nucleophilic substitution products [1]. Tosylates are commonly used as precusors for nucleophilic

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substitutions with [l8F]fluoride in radiopharmaceuticals. Tosyl chloride (TsCl), which is more reactive
than tosyl anhydride and p-toluenesulfonyl acid, is the most widely used tosylating agent. Preparation
of tosylates generally uses TsCl in the presence of a base, such as pyridine or triethylamine [2-4].
l8
Recently, as part of an intended F radiolabeling synthetic route (depicted in the Supplementary
Materials) we sought to prepare the corresponding tosylate by treatment of 5-hydroxy-7-(3-
bromoanilino)-3-cyano-pyrazolo[1,5-a]pyrimidine (1) with TsCl (Scheme 1) under typical conditions
[reaction of 1 mol equiv of an alcohol and 1.5 mol equiv of TsCl, with addition of a dichloromethane
solution of catalytic amount of 4-dimethylaminopyridine (DMAP) and 1.5 mol equiv of triethylamine
(TEA)]. Instead, we obtained the corresponding chloride 2. Consequently we carried out a series of
experiments and tried to discover why chlorination happened instead of tosylation.
Scheme 1. Formation of the chloride, not the desired tosylate.
Br
Br
NH
TsCl, DMAP, TEA
CH2Cl2
NH
N
N
N
N
HO
Cl
N
N
CN
CN
2
1
2. Results and Discussion
Treatment of o-, m- or p-nitro substituted benzyl alcohols with TsCl resulted in the formation of the
corresponding chlorides in moderate yields (entry 1~3 in Table 1), among which p-nitrobenzyl alcohol
gave in the highest yield (52%). 4-Nitrobenzyl bromide or iodide could be obtained by addition of
sodium bromide (or sodium iodide) and 4-nitrobenzyl alcohol to the TsCl/DMAP/TEA mixture in
dichloromethane (entry 4 and 5 in Table 1). The addition of sodium fluoride did not lead to the
formation of 4-nitrobenzyl fluoride. The reactions of 4-bromobenzyl alcohol and 3-chlorobenzyl
alcohol with TsCl also gave the corresponding chlorides in 30–35% yields (entry 6 and 7 in Table 1).
In contrast, benzyl tosylate was produced in 53% yield when benzyl alcohol without any electron
withdrawing substituent on the benzene ring reacted with TsCl (entry 8 in Table 1). The addition of KI
to the reaction mixture of benzyl alcohol and TsCl led to the formation of benzyl iodide in 49% yield
(entry 9 in Table 1).
The results could be rationalized by the following way. The reactions of benzyl alcohols with TsCl
usually gave the corresponding tosylates initially. The nucleophilic substitution of tosyl group by Cl−
would not occur when no electron withdrawing inductive effect exists in tosylates, such as benzyl
tosylate (entry 8 in Table 1) since Cl− in the reaction mixture was a very fair nucleophile; but benzyl
tosylate could be converted to benzyl iodide by a much better nucleophile I− (entry 9 in Table 1). The
reaction activity of benzyl tosylates could be improved when there was an electron withdrawing group,
such as a nitro group, Br− or Cl−, attached to the benzene ring due to the presence of electron
withdrawing inductive effect. Thus the nucleophilic substitutions of these activated benzyl tosylates by

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Cl− happened smoothly to give the corresponding chlorides despite the relatively poor nucleophilicity
of Cl− in the reaction mixture.
Table 1. Substituted benzyl alcohol chlorinations.
Entry
Alcohol
Product
Yield (%)
NO2
NO2
OH
Cl
1
42
3a
4a
O2N
O2N
OH
Cl
2
35
3b
4b
OH
Cl
O2N
O2N
3
4
5
6
52
47
45
33
4c
5
3c
Br
I
O2N
O2N
6
Br
Br
Cl
OH
Cl
3d
4d
Cl
7
31
53
OH
OH
Cl
3e
3f
4e
7
OTs
8
9
I
49
51
55
8
OH
Cl
10
O2N
O2N
4g
3g
OH
Cl
OCH3
OCH3
11
O
O
3h
4h
The pathway of the formation of the benzyl chorides is depicted in Scheme 2. TsCl reacted initially
with alcohol 3 to give tosylate 12. TEA coordinated with the HCl byproduct to give triethylammonium
hydrochloride and the nucleophilic chloride ion displaced the tosyl group to afford the substituted

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benzyl chloride 4. The nitro substituted benzyl chlorides were usually produced in higher yields than
bromo or chloro substituted benzyl chlorides, which might be due to the much stronger electron
withdrawing effect of the nitro group. 4-Nitrocinnamyl alcohol reacted with TsCl to give
4-nitrocinnamyl chloride in 51% yield (entry 10 in Table 1), which could be explained by the same
way as the formation of 4-nitrobenzyl chloride. Methyl mandelate was also used as a substrate and
treated with TsCl to produce methyl 2-chloro-2-phenylacetate in 55% yield (entry 11 in Table 1),
which indicated the intermediate tosylate was activated by the carbonyl group in the molecule and
reacted with Cl− to form the chloride.
Treatment of p-nitrobenzyl alcohol with N,N-dimethylformamide (DMF) instead of dichloromethane,
resulted in the formation of p-nitrobenzyl chloride in 87% yield, according to [5]. The results could
be explained by the effect that DMF as the polar aprotic solvent accelerated the nucleophilic
substitution reaction.
Scheme 2. Possible reaction pathway.
EWG
EWG
EWG
O
O S
O
TsCl
Et3N
CH3
OH
Cl
Et3NHCl
TsOHNEt3
3a-e, g, h
4a-e, g, h
12
Et3NH+Cl-
Treatment of p-methylbenzyl alcohol with TsCl resulted in the formation of the corresponding
chloride in 34% yield (entry 1 in Table 2). The reaction of p-methoxybenzyl alcohol with TsCl also
gave the corresponding chloride in 38% yield (entry 2 in Table 2).
Table 2. Substituted benzyl alcohol chlorinations.
Entry
Alcohol
Product
Yield (%)
OH
Cl
1
34
4i
3i
OH
Cl
MeO
MeO
2
3
38
31
4j
3j
OH
Cl
3k
4k
OH
Cl
4
36
3l
4l
Based on the above experiments, as depicted in Scheme 3, we envisaged that the formation of
tosylate 12 in situ by treating the alcohol 3 with tosyl chloride in the presence of base, followed by loss

Molecules 2011, 16
5669
of TsO− generates a cation 13, which was stabilized by the electron donating inductive effect of the
methyl or methoxy group. The benzyl cation 13 was subjected to simultaneous nucleophilic attack by
the chloride ion to afford the substituted benzyl chloride. The methoxybenzyl chloride was usually
produced in higher yield than methylbenzyl chloride, which might be due to the stronger electron
donating effect of methoxy group. 1-Phenylethanol reacted with TsCl to give 1-chloro-1-phenylethane
in 31% yield (entry 3 in Table 2), which could be explained by the same way as the formation
of p-methylbenzyl chloride. Diphenylmethanol was also used as a substrate to produce
chlorodiphenylmethane in 36% yield (entry 4 in Table 2) upon treatment with TsCl, which indicated
the benzyl cation was stabilized by the phenyl ring in the molecule and reacted with Cl− to form
the chloride.
Scheme 3. Possible reaction pathway.
EDG
EDG
EDG
EDG
O
O S
O
TsCl
Et3N
TsO-
+
CH3
OH
Cl
CH2
Et3NHCl
TsOHNEt3
13
Et3NH+Cl-
3i-l
4i-l
12
Treatment of 2-pyridinemethanol, 3-pyridinemethanol and 4-pyridinemethanol with TsCl resulted
in the formation of the corresponding chlorides in relatively low yields (entry 1–3 in Table 3). The
reaction of 4-nitro-2-pyridine methanol with TsCl also gave the corresponding chloride in 39% yield
(entry 4 in Table 3).
Table 3. Pyridine methanol chlorinations.
Entry
Alcohol
Product
Yield (%)
OH
Cl
1
22
N
N
N
N
9a
10a
OH
Cl
2
3
18
23
9b
9c
10b
N
N
OH
OH
Cl
10c
NO2
NO2
4
5
39
26
Cl
N
N
10d
9d
OTs
OH
N
N
11
9e

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5670
These results could be explained by the same way as benzyl alcohols. Pyridine methanols reacted
with TsCl to give the corresponding tosylates at first. The tosylates were activated to some extent since
the presence of the nitrogen atom in the pyridine ring distorted the electron distribution both in the
π-bonding system and in the σ-bonds and a strong destabilizing inductive effect took over because
the nitrogen atom was not directly attached to the electrophilic carbon. The nitro substituted
pyridinemethyl chloride was usually produced in higher yield than pyridinemethyl chlorides, which
might be due to the stronger electron withdrawing effect of nitro group. In contrast, treatment of
6-methyl-2-pyridinemethanol with TsCl led to the formation of 6-methyl-2-tosyloxy-methylpyridine
(entry 5 in Table 3), which meant that the electron donating effect of methyl group offset the opposite
effect of the nitrogen atom in the pyridine ring and the formed tosylate was not active enough to occur
nucleophilic substitution by Cl−.
In this system, using TsCl as chlorination reagent was a particularly mild method for the
transformation of alcohols to chlorides. In comparison with the traditional method for preparing
chlorides by convertion of an alcohol to a mesylate followed by treatment with LiCl [6], using TsCl
appeared to be a more convenient approach with respect to other reports [7-9].
3. Experimental
3.1. General
13
1H- and C-NMR spectra were recorded on a Bruker spectrometer operating in CDCl3 at 400 and
100 MHz, respectively. The IR spectra were recorded on a Nicolet-AVATAR 360 FT-IR spectrometer
using KBr pellets in the 4000–400 cm−1 regions. ESI-MS were performed on Waters LCT Premier XE.
EI-MS were performed on Bruker 320-MS.
3.2. General Procedure for Treatment of Alcohol with Tosyl Chloride
Alcohol (1 mmol), TEA (0.22 mL, 1.5 mmol) and DMAP (30 mg, 0.2 mmol) were added to CH2Cl2
(5 mL) at 0 °C. Then the solution of tosyl chloride (286 mg, 1.5 mmol) in CH2Cl2 (5 mL) was added
dropwise. The reaction mixture was stirred at 0 °C for 30 min then at 15 °C for 12 h. Water (10 mL)
was added, and then the organic phase was washed with saturated solution of NaHCO3 (10 mL × 2),
followed by brine. The organic layer was collected and dried over Na2SO4, and the solvent evaporated
under vacuum. The crude was purified by column chromatography (silica gel; petroleum ether/ethyl
acetate = 3:1) to afford the desired compound.
1
2-Nitrobenzyl chloride (4a). H-NMR (CDCl3): δ 4.98 (2H, s), 7.51 (1H, m), 7.63–7.70 (2H, m), 8.05
13
(1H, d, J = 8.1 Hz). C-NMR (CDCl3): δ 42.7, 125.2, 129.4, 131.6, 132.4, 133.7, 148.0. MS (ESI):
m/z = 171 [M+], 136 [M-Cl]+.
1
3-Nitrobenzyl chloride (4b). H-NMR (CDCl3): δ 4.66 (2H, s), 7.56 (1H, t, J = 7.9 Hz), 7.73 (1H, d,
13
J = 7.5 Hz), 8.18 (1H, dd, J = 7.0, 1.2 Hz), 8.27 (1H, s). C-NMR (CDCl3): δ 44.6, 123.3, 123.4,
129.8, 134.5, 139.4, 148.4. MS (ESI): m/z = 171 [M+], 136 [M-Cl]+.

Molecules 2011, 16
5671
1
4-Nitrobenzyl chloride (4c). H-NMR (CDCl3): δ 4.65 (2H, s), 7.58 (2H, d, J = 8.7 Hz), 8.22 (2H, d,
13
J = 8.7 Hz). C-NMR (CDCl3): δ 44.5, 123.9, 129.3, 144.3, 147.8. MS (ESI): m/z = 171 [M+], 136
[M-Cl]+, 125 [M-NO2]+.
1
4-Nitrobenzyl bromide (5). H-NMR (CDCl3): δ 4.52 (2H, s), 7.57 (2H, d, J = 8.7 Hz), 8.20 (2H, d,
13
J = 8.7 Hz). C-NMR (CDCl3): δ 30.9, 124.0, 129.9, 144.7, 147.8. MS (EI): m/z = 215 [M+], 136
[M-Br]+.
1
4-Nitrobenzyl iodide (6). H-NMR (CDCl3): δ 4.48 (2H, s), 7.54 (2H, d, J = 8.7 Hz), 8.15 (2H, d,
J = 8.7 Hz). 13C-NMR (CDCl3): δ 0.0, 122.1, 127.6, 144.8, 145.3. MS (EI): m/z = 263 [M+], 136
[M-I]+.
4-Bromobenzyl chloride (4d). 1H-NMR (CDCl3): δ 4.53 (2H, s), 7.27 (2H, d, J = 8.4 Hz), 7.48 (2H, d,
13
J = 8.4 Hz). C-NMR (CDCl3): δ 45.3, 122.5, 130.2, 131.9, 136.5. MS (EI): m/z = 204 [M+], 169
[M-Cl]+.
1
3-Chlorobenzyl chloride (4e). H-NMR (CDCl3): δ 4.54 (2H, s), 7.25–7.32 (3H, m), 7.39 (1H, s).
13C-NMR (CDCl3): δ 45.2, 126.6, 128.5, 129.8, 130.3, 134.5, 139.3. MS (EI): m/z = 160 [M+], 125
[M-Cl]+.
1
Benzyl tosylate (7). H-NMR (CDCl3): δ 2.44 (3H, s), 5.05 (2H, s), 7.24 (2H, m), 7.32 (5H, m), 7.78
13
(2H, d, J = 8.3 Hz). C-NMR (CDCl3): δ 21.6, 71.9, 127.1, 128.0, 128.5, 128.6, 129.0, 129.8, 133.3,
144.8.
1
Benzyl iodide (8). H-NMR (CDCl3): δ 4.46 (2H, s), 7.21–7.31 (3H, m), 7.37 (2H, m). 13C-NMR
(CDCl3): δ 5.6, 127.9, 128.7, 128.8, 139.3. MS (EI): m/z = 218 [M+], 91 [M-I]+.
1
4-Nitrocinnamyl chloride (4g). H-NMR (CDCl3): δ 4.26 (2H, dd, J = 5.7, 1.1 Hz), 6.50 (1H, dt,
J = 15.7, 6.8 Hz), 6.72 (1H, d, J = 15.7 Hz), 7.54 (2H, d, J = 8.8 Hz), 8.19 (2H, d, J = 8.8 Hz).
13C-NMR (CDCl3): δ 44.3, 124.0, 127.2, 129.6, 131.7, 142.3, 147.4. MS (EI): m/z = 197 [M+], 162
[M-Cl]+.
1
Methyl 2-chloro-2-phenylacetate (4h). H-NMR (CDCl3): δ 3.77 (3H, s), 5.36 (1H, s), 7.36–7.41
13
(3H, m), 7.49 (2H, m). C-NMR (CDCl3): δ 53.3, 58.9, 127.9, 128.9, 129.3, 135.7, 168.8. MS (EI):
m/z = 184 [M+], 125 [M-COOCH3]+.
4-Methylbenzyl chloride (4i). 1H-NMR (CDCl3): δ 2.34 (3H, s), 4.55 (2H, s), 7.16 (2H, d, J = 8.0 Hz),
7.26 (2H, d, J = 8.0 Hz). 13C-NMR (CDCl3): δ 21.2, 46.3, 128.6, 129.4, 134.6, 138.3. MS (EI):
m/z = 140 [M+], 105 [M-Cl]+.

Molecules 2011, 16
5672
1
4-Methoxybenzyl chloride (4j). H-NMR (CDCl3): δ 3.80 (3H, s), 4.56 (2H, s), 6.89 (2H, dm,
13
J = 8.7 Hz), 7.29 (2H, dm, J = 8.7 Hz). C-NMR (CDCl3): δ 46.3, 55.3, 114.4, 129.7, 130.1, 159.7.
MS (EI): m/z = 156 [M+], 121 [M-Cl]+.
1-Chloro-1-phenylethane (4k). 1H-NMR (CDCl3): δ 1.85 (3H, d, J = 6.8 Hz), 5.07 (1H, q, J = 6.8 Hz),
7.28 (1H, m), 7.34 (2H, m), 7.40 (2H, m). 13C-NMR (CDCl3): δ 26.5, 58.7, 126.5, 128.2, 128.6, 142.8.
MS (EI): m/z = 140 [M+], 105 [M-Cl]+.
1
Chlorodiphenylmethane (4l). H-NMR (CDCl3): δ 5.40 (1H, s), 7.23–7.42 (10H, m). 13C-NMR
(CDCl3): δ 80.0, 126.6, 127.3, 128.4, 142.2.
1
2-(Chloromethyl)pyridine (10a). H-NMR (CDCl3): δ 4.68 (2H, s), 7.25 (1H, m), 7.49 (1H, d,
J = 7.8 Hz), 7.71–7.76 (1H, td, J = 7.7, 1.8 Hz), 8.58 (1H, dm, J = 4.2 Hz). 13C-NMR (CDCl3): δ 46.7,
122.9, 123.1, 137.2, 149.2, 156.6. MS (ESI): m/z = 128.1 [(M+H)+].
3-(Chloromethyl)pyridine (10b). 1H-NMR (CDCl3): δ 4.60 (2H, s), 7.33 (1H, dd, J = 3.0, 4.8 Hz), 7.74
(1H, dt, J = 7.9, 1.9 Hz), 8.58 (1H, dd, J = 3.3, 1.5 Hz), 8.63 (1H, d, J = 2.0 Hz). 13C-NMR (CDCl3): δ
43.1, 123.7, 133.3, 136.3, 149.4, 149.6. MS (ESI): m/z = 128.1 [(M+H)+].
4-(Chloromethyl)pyridine (10c). 1H-NMR (CDCl3): δ 4.55 (2H, s), 7.34 (2H, d, J = 5.9 Hz), 8.62 (2H,
d, J = 5.9 Hz). 13C-NMR (CDCl3): δ 44.1, 123.0, 146.0, 150.1. MS (ESI): m/z = 128.1 [(M+H)+].
1
2-(Chloromethyl)-4-nitro-pyridine (10d). H-NMR (CDCl3): δ 4.81 (2H, s), 8.00 (1H, dd, J = 5.3,
13
2.0 Hz), 8.25 (1H, d, J = 1.9 Hz), 8.88 (1H, d, J = 5.3 Hz). C-NMR (CDCl3): δ 45.7, 115.4, 115.6,
151.6, 154.6, 160.0. MS (EI): m/z = 172 [M+].
6-Methyl-2-tosyloxymethylpyridine (11). 1H-NMR (CDCl3): δ 2.44 (3H, s), 2.48 (3H, s), 5.10 (2H, s),
7.08 (1H, d, J = 7.7 Hz), 7.23 (1H, d, J = 7.7 Hz), 7.34 (2H, d, J = 8.1 Hz), 7.57 (1H, t, J = 7.7 Hz),
7.82 (2H, d, J = 8.3 Hz). 13C-NMR (CDCl3): δ 21.5, 24.1, 71.9, 118.7, 122.8, 128.1, 129.8, 133.0,
137.1, 144.9, 153.1, 158.1. MS (ESI): m/z = 278.4 [(M+H)+].
4. Conclusions
In summary, we have shown that it was possible to predict whether chlorination or tosylation would
occur for substituted benzyl alcohols and pyridine methanols. The procedure was very mild and
operationally simple. For substituted benzyl alcohols, chlorination occurred when inductively electron
withdrawing groups or inductively electron donating groups were attached to the benzene ring. For
substituted pyridine methanols, tosylation occurred when inductively electron donating groups are
attached to the pyridine ring. These conclusions were useful for designing organic compound
l8
synthesis, especially for F labeled radiopharmaceuticals. Further exploration of the scope of TsCl
chlorination or tosylation reactions is underway and will be reported in due course.

Molecules 2011, 16
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Acknowledgement
The work was financially supported by National Natural Science foundation of China (No
21071022) and Beijing Key Subject Program. We also wish to thank Beijing Municipal Commission
of Education.
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© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).