LETTER
2885
Convenient One-Pot Synthesis of Sulfonyl Azides from Sulfonic Acids
S
ynthesis
o
of Sulfonyl
A
o
zide
s
from
n
i
g
ds -Gon Kim,a Doo Ok Jang*b
a
Biotechnology Division, Hanwha Chemical R&D Center, Daejeon 305-345, Korea
Department of Chemistry, Yonsei University, Wonju 220-710, Korea
Fax +82(33)7602182; E-mail: dojang@yonsei.ac.kr
b
Received 7 August 2008
O
S
O
S
Ph3P, Cl3CCN
Abstract: We have developed a one-pot process for preparing sul-
fonyl azides by treating sulfonic acids with trichloroacetonitrile,
triphenylphosphine, and sodium azide at room temperature. A wide
range of sulfonyl azides was synthesized in excellent yields under
mild conditions.
R
OH
R
N3
NaN3, MeCN, r.t.
O
O
Scheme 1
Key words: sulfonic acid, sulfonyl azide, trichloroacetonitrile,
triphenylphosphine, sodium azide
from sulfonic acids with trichloroacetonitrile, triphe-
nylphosphine, and sodium azide (Scheme 1).
We chose p-toluenesulfonic acid, which was dehydrated
by azeotropic distillation in benzene, as model substrate to
achieve optimal reaction conditions. Treating a solution of
p-toluenesulfonic acid (1 equiv), Ph3P (1 equiv), and
NaN3 (1 equiv) with Cl3CCN (1 equiv) in MeCN at room
temperature afforded sulfonyl azide in poor yield
(Table 1, entry 1). However, when the amount of Cl3CCN
and Ph3P was increased, the yield of sulfonyl azide in-
creased up to 92% (entry 3). An increase of the amount of
NaN3 made the required reaction time shorten (entry 4).
High reaction temperature caused a loss in the yield of sul-
fonyl azide with forming a nonpolar side product (entry
5). A large excess of trichloroacetonitrile and triphe-
nylphosphine was not efficient to improve the yield of sul-
fonyl azide (entry 6). We examined the reactivity of some
reagents to find suitable halogenating agents for preparing
sulfonyl chlorides such as Cl3CCOCCl3, Cl3CCO2Et,
Br3CCO2Et, and Cl3CCONH2 (entries 7–13). Trichloroace-
tonitrile is the choice of halogenating reagents.
Sulfonyl azides are versatile reagents for a variety of
chemical transformations. They have been used as valu-
able reagents for the preparation of a-diazocarbonyl re-
agents,1 the hydroazidation of olefins,2 the aziridation of
olefins,3 the radical amination,4 and metal-catalyzed cou-
pling reactions.5 Owing to a wide range of applications, a
general and convenient access to sulfonyl azides is highly
desirable.
The most practical laboratory method for preparing sulfo-
nyl azides involves the reaction of sulfonyl chlorides with
azides.6 The reaction requires the availability of sulfonyl
chlorides, which are troublesome to prepare and handle.
Generally, sulfonyl chlorides are prepared by treating sul-
fonic acids with chlorinating agents such as SOCl2,7
POCl2,8 PCl5,9 triphosgene,10 and cyanuric chloride.11
These methods have some drawbacks including low
yields of the desired product, using a large excess of high-
ly toxic chlorinating agents, and producing corrosive
byproducts. Alternatively, sulfonyl azides were prepared
by reacting sulfonyl anhydrides,12 a-disulfones,13 or 1-
sulfonylbenzotriazole14 with sodium azide. These meth-
ods suffer from difficulty in preparing the starting materi-
als. Thus, there is a great demand for the development of
convenient synthetic methods towards assessing sulfonyl
azides.
To investigate the generality and scope of the reaction,
various aryl and alkyl sulfonic acids were subjected to the
reaction conditions. Table 2 presents the results. All aryl
and aliphatic sulfonic acids gave excellent yields of sulfo-
nyl azides. Aryl sulfonic acids afforded somewhat higher
yields of sulfonyl azides than aliphatic sulfonic acids.
Aryl sulfonic acids with an electron-rich benzene ring ap-
pear to be more reactive, giving higher yields of product.
Aryl sulfonic acids with an electron-poor benzene ring af-
forded slightly lower yields of sulfonyl azides. The rela-
tive reactivity of aromatic sulfonic acids is consistent with
a mechanism involving attack on the sulfur atom of sulfo-
nyl group by a nucleophilic agent.
It has been reported that the combination of trichloroace-
tonitrile and triphenylphosphine is efficient for chlorinat-
ing carboxylic acids and sulfonic acids under mild
conditions.15 We envisioned that the combination of
trichloroacetonitrile and triphenylphosphine might pro-
vide a general protocol for preparing various sulfonyl
azides from sulfonic acids. We herein report a mild and
efficient procedure for the synthesis of sulfonyl azides
In summary, we developed a one-pot process for prepar-
ing sulfonyl azides from sulfonic acids with Cl3CCN,
Ph3P, and NaN3. The reaction provides convenience, effi-
ciency, and generality for the preparation of sulfonyl
azides from various sufonic acids. Employing less toxic
reagents make this process attractive from the standpoint
of environment.
SYNLETT 2008, No. 18, pp 2885–2887
1
4
.1
1
.2
0
0
8
Advanced online publication: 23.10.2008
DOI: 10.1055/s-0028-1083600; Art ID: U08208ST
© Georg Thieme Verlag Stuttgart · New York