Unusually stable, versatile, and pure arenediazonium tosylates: Their preparation, structures, and synthetic applicability

Article abstract of DOI:10.1021/ol8013528

(Graph Presented) A new, simple, and effective method for the diazotization of a wide range of arylamines has been developed by using a polymer-supported diazotization agent in the presence of p-toluenesulfonic acid. Various pure arenediazonium tosylates with unusual stabilities can be easily prepared by this method. As a result, these salts are useful and versatile substrates for subsequent transformations, such as halogenation and Heck-type reactions. The unusual stabilities of arenediazonium tosylates are also preliminarily discussed with their X-ray structures.

Full text of DOI:10.1021/ol8013528

ORGANIC
LETTERS
2008
Vol. 10, No. 18
3961-3964
Unusually Stable, Versatile, and Pure
Arenediazonium Tosylates: Their
Preparation, Structures, and Synthetic
Applicability
Victor D. Filimonov,*,† Marina Trusova,† Pavel Postnikov,†
Elena A. Krasnokutskaya,† Young Min Lee,‡ Ho Yun Hwang,‡
Hyunuk Kim,§ and Ki-Whan Chi*,‡
Department of Organic Chemistry, Tomsk Polytechnic UniVersity,
Tomsk 634050 Russia, Department of Chemistry, UniVersity of Ulsan,
Ulsan 680-749, Republic of Korea, and Department of Chemistry,
POSTECH, Pohang 690-784, Republic of Korea
filimonoV@tpu.ru; kwchi@ulsan.ac.kr
Received June 15, 2008
ABSTRACT
A new, simple, and effective method for the diazotization of a wide range of arylamines has been developed by using a polymer-supported
diazotization agent in the presence of p-toluenesulfonic acid. Various pure arenediazonium tosylates with unusual stabilities can be easily
prepared by this method. As a result, these salts are useful and versatile substrates for subsequent transformations, such as halogenation
and Heck-type reactions. The unusual stabilities of arenediazonium tosylates are also preliminarily discussed with their X-ray structures.
Aromatic diazonium salts are important building blocks not
only in classical organic synthesis but also in the preparation
of modern organic nanocompounds and the grafting of
organic molecules onto metallic or nonmetallic surfaces.1
Despite wide applicability in the synthesis of compounds
with a diazonium motif, diazonium salts have a serious
drawbackstheir intrinsic instability and explosive nature.
Because of this instability, subsequent reactions with dia-
zonium salts must be carried out in the same medium in
which they were produced. This restricts many chemists from
approaching potentially important transformations of these
salts.1a Thus, new diazonium salts that can be readily made,
are stable and explosion proof in a solid state for storage,
and have high versatility in organic reactions are both
desirable and necessary. These properties are peculiar to
aryldiazonium tetrafluoroborates,1b hexafluorophosphates,1c-f
and arenediazonium o-benezenedisulfonimides.2
† Tomsk Polytechnic University.
‡ University of Ulsan.
§
POSTECH.
(1) (a) Roglands, A.; Pla-Quintana, A.; Moreno-Manas, M. Chem. ReV.
2006, 106, 4622. (b) Cygler, M.; Przybylska, M.; Elofson, R. M. Can.
J. Chem. 1982, 60, 2852. (c) Zollinger, H. In The Chemistry of amino,
nitroso, nitro and related groups; Patai, S., Ed.; Wiley & Sons: New York,
1996; Supplement F2, Part 1, pp 636-637. (d) Godovikova, T. I.; Rakitin,
O. A.; Khmelnitskii, L. I. Russ. Chem. ReV. 1983, 52, 440. (e) Zollinger,
H. Diazo Chemistry I; VCH: Weinheim, 1994; p 24-25. (f) Galli, C. Chem.
ReV. 1988, 88, 765. (g) Tour, J. M. J. Org. Chem. 2007, 72, 7477. (h) Yu,
S. S. C.; Downnard, A. J. Langmuir 2007, 23, 4662. (i) Rostami, A. A.;
McDermott, M. T. e-J. Sci. Nanotech. 2006, 4, 419.
Other potential diazonium salts that meet these criteria are
arenediazonium arylsufonates, Ar1N2+ Ar2SO3 . About half
-
(2) (a) Barbero, M.; Crisma, M.; Degani, I.; Fochi, R.; Perracino, P.
Synthesis 1998, 1171. (b) Barbero, M.; Degani, I.; Dughero, S.; Fochi, R.
J. Org. Chem. 1999, 64, 3448.
10.1021/ol8013528 CCC: $40.75
Published on Web 08/23/2008
2008 American Chemical Society

a century has passed since some of their characteristics were
reported.3 Nevertheless, little attention has been focused on
them since, especially with regard to organic synthesis. They
have been prepared by ionic exchange from arenediazonium
-
Scheme 2
.
Diazotization of Arylamines by Using “Resin-NO2 ”
in the Presence of p-Toluenesulfonic Acid
chlorides Ar1N2 Cl- and used only for the production of azo-
+
dyestuffs and analytical purposes. Thus, the application of
most of these salts is new in organic synthesis, and their
properties and preparative synthetic methods have not been
reported.
We have recently shown that p-toluenesulfonic acid
(TsOH) serves as a mild acidic agent in one-step diazotiza-
-
and the reagent “Resin-NO2 ” for 5-20 min at room
temperature until the starting substrate disappeared (TLC).
The resin was removed by filtration, and the final product,
arenediazonium salts 1a-18a, were precipitated by adding
Et2O (Table 1).
tion-iodination of arylamines via intermediate, arenediazo-
4
nium tosylates ArN2 TsO-. We found that a few pure
+
arenediazonium tosylates can be prepared by diazotization
of arylamines using NaNO2 in a water paste (Scheme 1).5
Table 1. Isolated Yields of Arenediazonium Salts 1a-18a and
Their Melting Points
Scheme 1
.
Diazotization of Arylamines by NaNO2 in the
Presence of p-Toluenesulfonic Acid
+
entry
ArN2 TsO-
yield, %
mp, °C
63a
39a, 83b
42a, 72b
49a, 86b
82b
224
182
158-161
120
+
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
C6H5N2 (1a)
+
2-MeC6H4N2 (2a)
3-MeC6H4N2 (3a)
4-MeC6H4N2 (4a)
3,4-Me2C6H4N2 (5a)
2-MeOC6H4N2 (6a)
4-MeOC6H4N2 (7a)
4-NH2C6H4N2 (8a)
2-NO2C6H4N2 (9a)
3-NO2C6H4N2 (10a)
4-NO2C6H4N2 (11a)
4-NCC6H4N2 (12a)
2-HO2CC6H4N2 (13a)
4-HO2CC6H4N2 (14a)
4-IC6H4N2 (15a)
2,4,6-Br3C6H2N2 (16a)
+
+
+
182
51a,d
149-151
118-120
149-151
155
+
32a, 79b,d
66c,e
The similar solubility of formed arenediazonium tosylates
and TsONa, however, complicates their separation and
creates unwanted disposal issues of the diazonium products
during the purification process. Thus, the development of a
new method to circumvent this problem is necessary.
We report a new, efficient method for the production of
pure arenediazonium tosylates and their physical and chemi-
cal characteristics. We have developed a new diazotization
method of aminoarenes 1-18 in the presence of TsOH by
using a polymer-supported diazotization reagent. The prepa-
+
+
35a, 95b
54a, 85b
39a, 84b
32a, 97b
82b
+
134f
+
132g
+
+
124
128
+
80b
114-115
124-126
152
134-136
246
+
60a
+
58a
+
+
2-C10H7N2 (17a)
+N2C6H4CH2C6H4N2 (18a)
84a
25c,e
+
-
ration of the polymer-supported nitrite (“Resin-NO2 ”) was
a Diazotization occurred at rt in water for 20 min. Molar ratio of
amine/”Resin-NO2-”/TsOH: 1:1:1. b Molar ratio of amine/”Resin-NO2-”/
TsOH: 1:3:3. c Molar ratio of amine/”Resin-NO2-”/TsOH: 1:6:6. d Reaction
time 5 min. e MeOH as a solvent. f Lit.3c mp 131-132 °C. g Lit.3c mp
141-142 °C.
achieved by ion exchange of porous tetramethylammonium
hydroxide resin AV-17-86 or Amberlyst A26 with an aqueous
solution of NaNO2. A similar polymer-supported agent has
been used for the generation of a few arenediazonium
chlorides in aqueous HCl.7
Diazotization of various aromatic amines 1-18 (Scheme
2) was easily carried out by stirring glacial AcOH or MeOH
solution with the appropriate amine, p-toluenesulfonic acid,
Our new method is safer, cheaper, and more convenient
than the previous diazotization with alkyl nitrites, for
example, in the synthesis of stable arenediazonium o-
benezenedisulfonimides.2 In general, our diazotization method
is applicable for various anilines with electron-donating as
well as electron-accepting substituents and even for the
sterically congested aniline 16.
(3) (a) Saunders, K. H. The Aromatic Diazo-Compounds and their
Technical Applications; Edward Arnold & Co.: London, 1949; p 83. (b)
Hodgson, H. H.; Marsden, E. J. Chem. Soc. 1940, 208. (c) Kikot, B. S.;
Kolesnik, Yu. A. Zh. Obshch. Khim. 1963, 33, 997–1001.
(4) Krasnokutskaya, E. A.; Semenischeva, N. I.; Filimonov, V. D.;
Knochel, P. Synthesis 2007, 81.
Isolated yields of salts 1a-18a (Table 1) depend upon
the ratio of reagents added. The optimal molar ratio of an
(5) Gorlushko, D. A.; Filimonov, V. D.; Krasnokutskaya, E. A.;
Semenisheva, N. A.; Go, B. S.; Hwang, H. Y.; Cha, E. H.; Chi, K.-W.
Tetrahedron Lett. 2008, 49, 1080.
-
amine/Resin-NO2 /TsOH is 1:3:3 in general, but for the best
(6) AV-17-8 is Russian analogue of Amberlyst A26 hydroxide form;
0.4-1.2 mm polystyrene beads with 16% DVB cross-linking and a loading
of 4.3 mmol/g. Resin-NO2- reagent was prepared by the addition of resin
AV-17-8 (3.5 g) into a solution of NaNO2 (2.07 g, 30 mmol) in water (30
yield of amino salt 8a, a ratio of 1:6:6 is necessary. Our
attempts to prepare double-diazonium salt (+N2C6H4N2 ,
+
2TsO-) from p-phenylenediamine (8) were unsuccessful and
only resulted in 8a. However, in the case of 4,4′-methyl-
enedianiline (18) bearing two isolated NH2 groups, it was
possible to produce the double salt 18a in a low yield. Acetic
acid was an unsuitable solvent for the diazotization of
-
mL). The mixture was stirred at rt for 10 min. Resin-NO2 was filtered
and washed with water until the pH of filtrate became neutral. The content
-
of prepared Resin-NO2 was 3.5 mmol of NO2-/g.
(7) (a) Caldarelli, M.; Baxendale, I. R.; Ley, S. V. Green Chem. 2000,
2, 43. (b) Merrington, J.; James, M.; Bradley, M. Chem. Commun. 2002,
140.
3962
Org. Lett., Vol. 10, No. 18, 2008

Figure 1. X-ray crystal structures of (a) 9a, (b) 12a, and (c) 15a with multiple close contacts between nitrogen atoms of arenediazonium
cations and oxygen atoms of tosylate anions.
strongly basic diamines 8 and 18. On the contrary, salts 8a
and 18a could be provided if methanol was used as a solvent
instead.
nediazonium tosylates in particular show multiple and close
contacts between the nitrogen atoms in diazonium cations
and the oxygen atoms of tosylate anions through charge-
charge interactions (Figure 1). The shortest distances between
the nitrogen atoms of a cation and the oxygen atoms of the
corresponding tosylates in 9a, 12a, and 15a are 2.673, 2.770,
and 2.744 Å, respectively, which are much shorter than the
sum of van der Waals radii (2.90 Å).9 Therefore, we believe
that such an intimate interaction between cations and anions
might be a crucial clue for the unusual stability of arene-
diazonium tosylates. To our knowledge, this is the first
example of the stabilization of diazonium groups by multiple
and close contacts with counter tosylate anions, which is
clearly elucidated by X-ray crystallography.
Despite their high thermal and aging stability, all arene-
diazonium tosylates 1a-18a showed good reactivity in
subsequent transformations. Apart from mentioned azo-
coupling reactions, selected salts were tried in typical
conversions of diazonium salts. These salts effectively react
at room temperature with KI, KBr, or NaNO2 in water to
give the corresponding products of nucleophilic replacement
in high yields (Scheme 3, Table 2). It is important to note
The 1H and 13C NMR and IR spectra confirm the structures
of prepared salts 1a-18a, and the structures of 9a, 12a, and
15a were also supported by X-ray analysis (Figure 1).
The structures and diazonium nature of 1a-18a were also
verified by azo-coupling reactions with 2-naphthol to give
the expected (2-hydroxy-1-naphthyl)aryldiazenes in higher
than 90% yields. In addition, salts 1a-18a are very soluble
not only in protic solvents (AcOH, MeOH, EtOH, and H2O)
but also in polar aprotic ones (DMSO, DMF, and MeCN);
their good solubility is an important advantage over other
arenediazonium tetrfluoroborates or hexafluoro phosphates.
The prepared salts 1a-18a are slightly colored solids that
have well-defined melting points. One property that makes
diazonium salts 1a-18a very useful is their excellent
stability, a feature that could lead to important synthetic
developments. Pure salts 1a-18a stored at room temperature
in the dark for a few months underwent no changes. Even
under sunlight, salt 11a survived at room temperature without
decomposition for two weeks. Thus, arenediazonium tosy-
lates 1a-18a can be stored under normal conditions like
other stable organic compounds.
Thermal stabilities of 1a-18a were carefully tested by
DSC between 0-600 °C under a nitrogen atmosphere, and
no explosive phenomenon was observed for any of the salts.
The only exception is salt 9a, in which a weak explosive
phenomenon was observed at 200-205 °C during a heating
process above its melting point. This result may be caused
not by disintegration of 9a but as a byproduct of its
decomposition.
Scheme 3. Selected Reactions of Arenediazonium Tosylates
To gain an insight into the thermal stability of arenedia-
zonium tosylates, we determined crystal structures of these
compounds by X-ray crystallography. After numerous un-
successful attempts, single crystals of 9a, 12a, and 15a
suitable for X-ray analysis using synchrotron radiation were
finally grown from an acetic acid and diethyl ether solution.
The X-ray crystal structures of arenediazonium tosylates
reveal that one independent arenediazonium cation is sur-
rounded by three tosylate anions. Unlike the reported crystal
structure8 of unstable benzenediazonium chloride (NsCl
3.22-3.56 Å in Figure S12, Supporting Information), are-
that these reactions successfully proceed in the absence of
cupreous salts.
Salt 11a gives triazene 19 in 97% yield by the treatment
with piperidine in methanol, and salts 11a, 13a,and 14a are
capable of styrene arylation in the presence of Pd(OAc)2 to
Org. Lett., Vol. 10, No. 18, 2008
3963

can be easily prepared in a pure, dry state. Due to their
excellent stability, they can be stored safely for a long time
and be readily used for subsequent transformations. These
salts reveal good solubility in many solvents and high
reactivity in a typical reaction of diazonium salts. We believe
that arenediazonium tosylates have good potential to be
useful and versatile building blocks in organic synthesis.
Table 2. Reaction Results of Arenediazonium Tosylates with
Nucleophilic Reagents at Room Temperature in Water
salt
reagent
time, min
product, yield (%)
7a
8a
9a
KI
KI
KI
KI
KI
KI
KI
KI
30
50
10
5
20
200
240
10
60
100
30
p-MeOC6H4I, 80
p-NH2C6H4I, 100
o-NO2C6H4I, 97
p-NO2C6H4I, 98
p-NCC6H4I, 64
o-HO2CC6H4I, 93
p-HO2CC6H4I, 91
2,4,6-Br3C6H2I, 97
p-NO2C6H4Br, 80
p-NCC6H4Br, 74
p-(NO2)2C6H4, 74
11a
12a
13a
14a
16a
11a
12a
11a
Acknowledgment. We gratefully acknowledge the BK 21
program of the Korean Ministry of Education for the support
of this work. X-ray diffraction experiments using synchrotron
radiation were performed at the Pohang Accelerator Labora-
tory supported by MOST and POSTECH.
KBr
KBr
NaNO2
Supporting Information Available: Experimental details,
1H and 13C NMR spectral data, and X-ray crystallographic
results. This material is available free of charge via the
Internet at http://pubs.acs.org.
provide corresponding (E)-stilbenes 20-22 respectively
(Scheme 3).
In conclusion, we have developed a new, simple, and
effective method for the diazotization of a wide range of
aryl amines by using a polymer-supported diazotization agent
in the presence of p-toluenesulfonic acid. Various arenedia-
zonium tosylates as a little-known class of diazonium salts
OL8013528
(8) Romming, C. Acta Chem. Scand. 1963, 17, 1444.
(9) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Ithaca: Cornell
University, 1960.
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Org. Lett., Vol. 10, No. 18, 2008