A green procedure for the diazotization-iodination of aromatic amines under aqueous, strong-acid-free conditions

Article abstract of DOI:10.1055/s-0030-1260046

A convenient and mild one-pot method for the synthesis of iodoarenes in high yields by the sequential diazotization-iodination of aromatic amines with a reusable polymeric diazotization agent in the presence of p-toluenesulfonic acid at room temperature in water was developed. The method is general and is the greenest alternative of the known diazotization-iodination methods. The method is also effective for the preparation of 1H-benzo[d][1,2,3]triazole and benzo[d][1,2,3]thiadiazole. Georg Thieme Verlag Stuttgart ? New York.

Full text of DOI:10.1055/s-0030-1260046

2
154
PAPER
A Green Procedure for the Diazotization–Iodination of Aromatic Amines
under Aqueous, Strong-Acid-Free Conditions
a
a
a
b
b
D
M
iazotization–Iodinati
a
A
rom
r
atic
A
m
i
s
na E. Trusova, Elena A. Krasnokutskaya, Pavel S. Postnikov, Younghwa Choi, Ki-Whan Chi,*
a
Victor D. Filimonov*
a
Department of Organic Chemistry, National Research Tomsk Polytechnic University, Tomsk 634050, Russian Federation
E-mail: filimonov@tpu.ru
Department of Chemistry, University of Ulsan, Ulsan 680-749, Republic of Korea
E-mail: kwchi@ulsan.ac.kr
b
Received 7 April 2011
tive reagents, alkyl nitrites, are not very suitable for diazo-
tization on an industrial scale, since they are expensive,
decompose during storage, and are corrosive. Moreover,
Abstract: A convenient and mild one-pot method for the synthesis
of iodoarenes in high yields by the sequential diazotization–iodina-
tion of aromatic amines with a reusable polymeric diazotization
agent in the presence of p-toluenesulfonic acid at room temperature alkyl nitrites generally can diazotize aromatic amines only
in water was developed. The method is general and is the greenest in organic solvents (e.g., Et O, MeCN, THF), but not in
2
alternative of the known diazotization–iodination methods. The
method is also effective for the preparation of 1H-ben-
zo[d][1,2,3]triazole and benzo[d][1,2,3]thiadiazole.
water. It should also be taken into account that diazonium
salts obtained under classical conditions are potentially
explosive substances.
Key words: diazotization, halogenation, iodination, heterocycles,
Little work on the diazotization of aromatic amines in a
amines
weakly acidic medium using nontoxic, nonflammable,
and explosive-free conditions has been reported. Tundo et
5
al. reported a diazotization–iodination with sodium ni-
Aromatic iodides are versatile reagents that can be con-
trite and potassium iodide in a liquid carbon dioxide/water
solvent system at 65 bar for a small number of anilines;
however, in some of the cases, diazotization was accom-
panied by the formation of triazenes and biphenyls. A
convenient and rapid method for the synthesis of iodo-
arenes in good yields has recently been developed; it in-
volves the sequential diazotization–iodination of aromatic
1
verted into a wide variety of materials. Many iodoarenes
are biologically active molecules that are used in medicine
2
and biochemistry. Although significant developments
have been achieved in the synthesis of iodoarenes, their
preparation via direct iodination has some limitations.3
Direct electrophilic iodination is often carried out under
harsh reaction conditions in the presence of toxic oxidants
amines with sodium nitrite, solid silica sulfuric acid, and
and frequently gives a mixture of isomers due to the lack
6
potassium iodide by grinding in a mortar. This method
of regioselectivity for this reaction. Since aromatic amines
proved to be applicable to various aromatic amines, but
are generally available, most methods for the preparation
the grinding of the reaction components in a mortar can-
of substituted aromatic iodides have focused on improv-
not presently be implemented on a large scale, and the di-
ing the diazotization–iodination reaction.
azotization stage was accompanied by the release of
Usually diazotization–iodination of aromatic amines is nitrogen oxides, as is common with other diazotization
carried out in two steps by means of sodium nitrite in a conditions using sodium nitrite.
strongly acidic medium (H SO , HCl) at low temperature
2
4
Recently we have shown that a sulfonic cation-exchange
resin, p-toluenesulfonic acid (p-TsOH), or sodium hydro-
gensulfate are mildly acidic agents for the diazotization–
halogenation of aromatic amines with sodium nitrite or
tert-butyl nitrite in acetonitrile, water, or water pastes.7
However, the use of sodium nitrite or alkyl nitrite in these
methods makes the release of gaseous nitrogen oxides dif-
ficult to avoid, and the above-mentioned problems with
scaling up the process would still be an issue. Thus, the
development of a new method to circumvent these prob-
lems is necessary.
4
or by means of alkyl nitrites in organic solvents followed
by reaction with iodine or potassium iodide, often in the
presence of copper salts. Both of these approaches to the
diazotization step do not meet the requirements of green
chemistry for the following reasons. First, the use of sodi-
um nitrite as the diazotizing agent is almost always ac-
companied by the release of nitrogen oxides, an issue
particularly with industrial-scale reactions. Second, the
isolation of iodination products from strongly acidic solu-
tion requires a neutralization stage, which generates large
quantities of salts. In addition, a strongly acidic environ-
ment for the diazotization cannot be tolerated by amines
containing acid-sensitive functional groups. The alterna-
We have also recently shown that anion-exchange resins
saturated with nitrite ions from sodium nitrite are conve-
nient and mild polymer-supported diazotization reagents
–
(
‘Resin NO ’) for the synthesis of stable arenediazonium
2
tosylates from aromatic amines and p-toluenesulfonic
acid in acetic acid. A similar polymer-supported reagent
has been used to generate a few arenediazonium chlorides
SYNTHESIS 2011, No. 13, pp 2154–2158
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Advanced online publication: 13.05.2011
DOI: 10.1055/s-0030-1260046; Art ID: Z36811SS
Georg Thieme Verlag Stuttgart · New York
©

PAPER
Diazotization–Iodination of Aromatic Amines
2155
9
–
in aqueous hydrogen chloride. ‘Resin NO ’ is readily dide was added to the solution, and the solution was
2
obtained and is stable to storage at room temperature in a stirred at room temperature for the period of time speci-
moist state for at least one month (see experimental sec- fied in Table 1. After the addition of potassium iodide, ni-
tion). Until now, this reagent has not been used for the di- trogen bubbling was immediately observed, and aryl
azotization of aromatic amines in water or for one-pot iodides 1a–13a precipitated from the water.
diazotization–iodination reactions.
–
1) ‘Resin NO –’, p-TsOH, H O, r.t.
We have found that simply stirring ‘Resin NO ’ with the
2 2
2
2
) KI, r.t.
aromatic amines 1–13 in water in the presence of p-tolu-
enesulfonic acid at room temperature for 20–30 minutes
leads to complete conversion of the starting amines
ArNH3
–13
ArI
+
N2
1
1a–13a
Scheme 1 Preparation of aryl iodides 1a–13a by the aqueous, one-
pot diazotization–iodination method
(
Scheme 1, Table 1). In these reactions, the release of ni-
trogen oxides or other gaseous substances was never ob-
served. After filtration of the resin, a pure and stable
aqueous solution of the corresponding arenediazonium to-
+
–
10
sylate (ArN TsO ) was obtained. Next, potassium io-
2
–
2
a
Table 1 Diazotization–Iodination of Aromatic Amines 1–13 by Using the Polymeric Diazotization Agent ‘Resin NO ’
Aromatic amine
Time (min) Product
Yield (%)
Mp (°C)
NH2
I
I
COOH
COOH
74 (50b)
161–163 (162)11
1
2
300
270
1a
2a
NH2
85 (52b)
266–268 (270)11
COOH
NH2
COOH
I
3
4
5
90
90
90
3a
4a
5a
95 (89a)
170 (171)11
NO2
NH2
NO2
I
NO2
NO2
52 (52–53)7a
91
NH2
I
88
122–124 (124–128)14
CN
CN
I
NH2
6
75
6a
91
oil
NH2
I
7
8
70
75
7a
8a
91
94
53–55 (52)11
OMe
NH2
OMe
I
OMe
OMe
oil
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156
M. E. Trusova et al.
PAPER
–
a
Table 1 Diazotization–Iodination of Aromatic Amines 1–13 by Using the Polymeric Diazotization Agent ‘Resin NO ’ (continued)
2
Aromatic amine
Time (min) Product
Yield (%)
98
Mp (°C)
NH2
I
9
0
90
9a
64 (63–65)15
NH2
NH2
NH2
Br
I
Br
Br
Br
Br
1
1
120
10a
81
55
103–104 (104–105)16
Br
NH2
I
1
60
11a
88–90 (89–90)17
N
N
N
N
1
1
2
3
120
90
12a
13a
80
84
92–94 (93–94)12
52–54 (53)11
H2N
NH2
I
I
NH2
I
a
–
Reaction conditions: 1. Amine 1–13 (1 equiv), ‘Resin NO ’ (2 equiv), p-TsOH (3 equiv), H O, 20 °C; 2. KI (2.5 equiv), 20 °C.
Reactions in the presence of HCl instead of p-TsOH.
2
2
b
–
An optimal ratio of reactants was found to be aromatic reused for the preparation of ‘Resin NO ’. The diazotiza-
2
–
–
substrate/‘Resin NO ’/KI/p-TsOH = 1:2:2.5:3. The solid tion activity of this recycled ‘Resin NO ’ did not decrease
2
2
products 3a, 4a, 5a, and 9a–13a were easily filtered from after at least three cycles of regeneration.
the aqueous medium, then washed with water, and dried.
Another advantage of this method is its relative safety,
For isolation of the oily products 1a, 2a, 6a, 7a, and 8a,
ethyl acetate was used for extraction. Analysis of the wa-
ter reaction solutes by gas chromatography and thin-layer
chromatography did not show phenolic compounds, triaz-
enes, or biphenyls as possible side products. The running
of both stages of the diazotization–iodination process was
very easy to control. Thus, thin-layer chromatography
was a convenient method for determining the end of the
first stage of the diazotization reaction, because the disap-
pearance of the starting amine spot could be observed.
The iodination step was carried out until the intermediate
diazonium tosylate was exhausted; this was simply deter-
mined by the negative probe with b-naphthol.
since it uses aqueous solutions of arenediazonium tosy-
lates, which have been shown to be stable even in the dry
state.8
It should be noted that performing a single-step diazotiza-
tion–iodination reaction of aromatic amines with ‘Resin
–
NO ’ and p-toluenesulfonic acid in the presence of potas-
2
sium iodide in water leads to incomplete conversions of
the starting amines and the formation of iodine and gas-
eous products. This is presumably due to active diazoti-
+
zating intermediates (probably HNO , NO , or TsONO)
2
being partially consumed in the oxidation of iodide ion to
iodine.
Typically, the diazotization–iodination reactions were run
with two mmol of starting amine, but in the case of 4-ami-
nobenzonitrile (5), scaling up to six mmol did not reduce
the yield of 4-iodobenzonitrile (5a).
It is important to note that the solid aryl iodides 3a, 4a, 5a,
and 9a–13a have fairly high NMR and GC-MS purity and
can be used in further reactions without additional purifi-
cation; i.e., in these cases, the use of organic solvents was
not necessary in any stage of the diazotization iodination The procedure proved to be applicable to aromatic amines
process. This approach would be especially suitable for of various structures 1–13, both strongly and weakly ba-
combinatorial chemistry.
sic, polycyclic, and also sterically crowded (tribromo-
aniline 10) amines; i.e., the method is generally applicable
After the diazotization reaction, the filtered resin was
washed with acetone and alkaline solution and could be
(
for exceptions, see below). In general, we did not observe
any clear correlations between reaction time, electronic
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PAPER
Diazotization–Iodination of Aromatic Amines
2157
and steric effects of substituents on the aromatic ring, and sulting water solutes of arenediazonium tosylates gently
aryl iodide yield (Table 1). This occurrence is rather com- react with potassium iodide to provide pure iodoarenes,
mon for the reactivity of aromatic arenediazonium salts in which do not need further purification. In the case of o-
which substituents often produce opposing effects at dif- phenylenediamine and o-thioaniline, the products benzo-
4
ferent stages of the reaction mechanism. Yields of isolat- triazole and benzothiadiazole form in excellent yields. In
ed iodoarenes were good or excellent, except for 4- general, this method, which features the use of a weakly
iodoazobenzene 11a (Table 1). Although we cannot yet acidic, aqueous medium, is run at room temperature, is
fully explain this exception, part of the starting 4-amino- characterized by ease of isolation of sufficiently pure
–
azobenzene probably interacts with the ‘Resin NO ’ in products and the absence of side products, and allows re-
2
the diazotization step and/or gives water-soluble byprod- cycling of the diazotization reagent, meets the require-
ucts.
ments of a green chemistry process when compared with
other known diazotization–iodination methods.
In the case of o-phenylenediamine (14) and o-sulfanyl-
aniline (15), the diazotization reaction with ‘Resin NO ’
–
2
in water and subsequent reaction with potassium iodide All starting reagents were ACS grade and were employed without
provides only the cyclization products, 1H-ben- further purification. Melting points were determined with a Boetius
melting point apparatus and are uncorrected. NMR spectra were re-
corded on a Bruker Avance 300 instrument. GC-MS spectra were
obtained on an Agilent 7890/5975C instrument.
zo[d][1,2,3]triazole (14a) and benzo[d][1,2,3]thiadiazole
(
15a), which were isolated in yields of 97% and 96%, re-
spectively (Scheme 2). The same heterocyclic products
are known to form from diazotization of compounds 14
–
Polymeric Diazotization Reagent ‘Resin NO ’
2
4
and 15 with sodium nitrite, and our approach seems to be Anion-exchange resin AV-17-8 (Russia) or Amberlist A26 (Ald-
an efficient and green alternative to the traditional meth- rich) (3.5 g) was added to a soln of NaNO (2.07 g, 30 mmol) in H O
2
2
–
(
30 mL). The mixture was stirred at r.t. for 10 min. ‘Resin NO ’
ods. We have not investigated why only the cyclization of
intermediate diazonium salts from compounds 14 and 15
take place under the action of potassium iodide instead of
iodination. We can note that products 14a and 15a are also
formed in the absence of potassium iodide, but slowly and
in lower yields.
2
was filtered and washed with H O until the pH of the filtrate became
2
neutral. The ion-exchange capacity of prepared samples of ‘Resin
–
–
NO ’ was 2.6–3.6 mmol of NO /g and did not decrease during
2
2
storage in a moist state for at least one month.
Diazotization–Iodination of Aromatic Amines 1–13; General
Procedure
–
–
–
‘Resin NO ’ (2.3 g, 6 mmol of NO ) was added to a soln of p-
2
2
1
2
) ‘Resin NO2 ’, p-TsOH, H2O, r.t.
) KI, H2O
NH2
NH2
N
TsOH·H O (1.14 g, 6 mmol) in H O (5 mL), and the reaction mix-
2
2
N
ture was stirred for 1–2 min. Then aromatic amine 1–13 (2 mmol)
was slowly added, the reaction mixture was stirred for 20–30 min at
r.t. until disappearance of the starting amine (by TLC), and the resin
was removed by filtration. Next, KI (0.83 g, 5 mmol) was added to
the resulting aqueous soln, and stirring was continued until N bub-
ble evolution ceased, for the period of time specified in Table 1. The
97%
N
H
14
14a
–
1
2
) ‘Resin NO2 ’, p-TsOH, H2O, r.t.
) KI, H2O
SH
S
N
2
N
96%
aqueous soln was decolorized with Na SO . Solid products (3a, 4a,
NH2
2
3
15
15a
5a, 9a–13a) were filtered, washed with H O, and dried. Oily prod-
2
ucts (1a, 2a, 6a, 7a, 8a) were extracted with EtOAc (3 × 15 mL),
Scheme 2 Preparation of 1H-benzo[d][1,2,3]triazole (14a) and ben-
and the organic layer was washed with H O (3 × 10 mL) and dried
2
–
zo[d][1,2,3]thiadiazole (15a) by diazotization with ‘Resin NO ’
2
(MgSO ), and the solvent was evaporated in vacuo; this afforded the
4
corresponding iodoarenes.
It is important to note that only the combination of the
4
-Iodobenzoic Acid (2a)
–
polymer diazotizating agent ‘Resin NO ’ and p-toluene-
2
11
Yield: 85%; mp 266–268 °C (Lit. 270 °C).
1H NMR (300 MHz, DMSO-d
sulfonic acid provides the above results. Thus, the use of
–
6
): d = 7.94 (d, J = 7.8 Hz, 2 H), 7.81
sodium nitrite instead of ‘Resin NO ’ in the presence of
2
(
d, J = 7.8 Hz, 2 H).
p-toluenesulfonic acid leads to an appreciable release of
nitrogen oxides during the process of diazotization of
1
3
C NMR (75 MHz, DMSO-d ): d = 164.8, 130.0, 128.1, 99.4.
6
anilines 1–15. On the other hand, the diazotization of aro-
Bis(4-iodophenyl)methane (12a)
Yield: 80%; mp 92–94 °C (Lit. 93–94 °C).
–
matic amines 1–3 by ‘Resin NO ’ in the presence of hy-
12
2
drogen chloride instead of p-toluenesulfonic acid requires
at least 10–11 equivalents of hydrogen chloride for com-
plete conversion of the starting amines and provides lower
yields of the iodinated products 1a–3a in the subsequent
reaction with potassium iodide (see Table 1).
1
H NMR (300 MHz, DMSO-d ): d = 7.60 (d, J = 7.8 Hz, 4 H), 6.91
6
(
1
d, J = 7.8 Hz, 4 H), 3.87 (s, 2 H).
3
C NMR (75 MHz, DMSO-d ): d = 140.2, 137.7, 131.2, 91.9, 41.0.
6
1
H-Benzo[d][1,2,3]triazole (14a) and Benzo[d][1,2,3]thiadiazole
In conclusion, we have developed an efficient and exper- (15a)
–
–
‘
Resin NO ’ (2.3 g, 6 mmol of NO ) was added to a soln of p-
imentally simple one-pot method for the diazotization–
2
2
TsOH·H O (1.14 g, 6 mmol) in H O (5 mL), and the reaction mix-
ture was stirred for 1–2 min. Then aromatic amine 14 or 15 (2
mmol) was slowly added, the reaction mixture was stirred for 30
2
2
iodination of aromatic amines that utilizes the polymeric
–
diazotization reagent ‘Resin NO ’ in the presence of p-
2
toluenesulfonic acid in water at room temperature. The re-
Synthesis 2011, No. 13, 2154–2158 © Thieme Stuttgart · New York

2
158
M. E. Trusova et al.
PAPER
min at r.t. until disappearance of the starting amine (by TLC), and
the resin was removed by filtration. Next, KI (0.83 g, 5 mmol) was
added to the resulting aqueous soln, and stirring was continued for
(3) (a) Hanson, J. R. J. Chem. Res. 2006, 277. (b) Stavber, S.;
Jereb, M.; Zupan, M. Synthesis 2008, 1487.
(4) Zollinger, H. Diazo Chemistry I: Aromatic and
Heteroaromatic Compounds; VCH: Weinheim, 1994.
(5) Tundo, P.; Loris, A.; Selva, M. Green Chem. 2007, 9, 777.
(6) Zarei, A.; Hajipour, A. R.; Khazdooz, L. Synthesis 2009,
941.
1
5 min. The aqueous soln was decolorized with Na SO and extract-
2 3
ed with CH Cl (3 × 15 mL), the organic layer was washed with
2
2
H O (3 × 10 mL) and dried (MgSO ), and the solvent was evaporat-
2
4
ed in vacuo; this afforded the corresponding product 14a or 15a.
(
7) (a) Filimonov, V. D.; Semenischeva, N. I.; Krasnokutskaya,
E. A.; Tretyakov, A. N.; Hwang, H. Y.; Chi, K.-W. Synthesis
2008, 185. (b) Krasnokutskaya, E. A.; Semenischeva, N. I.;
Filimonov, V. D.; Knochel, P. Synthesis 2007, 81.
1
H-Benzo[d][1,2,3]triazole (14a)
1
3a
Yield: 97%; mp 95–97 °C (Lit. 98 °C).
1
H NMR (300 MHz, DMSO-d ): d = 7.21 (d, J = 7.8 Hz, 2 H), 7.61
6
(c) Gorlushko, D. A.; Filimonov, V. D.; Krasnokutskaya, E.
(
d, J = 7.8 Hz, 2 H), 8.24 (s, 1 H).
A.; Semenischeva, N. I.; Go, B. S.; Hwang, H. Y.; Cha, E.
H.; Chi, K.-W. Tetrahedron Lett. 2008, 49, 1080,.
1
3
C NMR (75 MHz, DMSO-d ): d = 138.09, 121.71, 115.31.
6
(
d) Gorlushko, D. A.; Filimonov, V. D.; Semenishcheva, N.
Benzo[d][1,2,3]thiadiazole (15a)
Yield: 96%; mp 35 °C (Lit. 35 °C).
I.; Krasnokutskaya, E. A.; Tret’yakov, A. N.; Chi, K.-W.
Russ. J. Org. Chem. 2008, 44, 1243. (e) Lee, Y. M.; Moon,
M. E.; Vajpayee, V.; Filimonov, V. D.; Chi, K.-W.
Tetrahedron 2010, 66, 7418. (f) Moon, M. E.; Choi, Y.;
Lee, Y. M.; Vajpayee, V.; Trusova, M.; Filimonov, V. D.;
Chi, K.-W. Tetrahedron Lett. 2010, 51, 6769.
1
3b
1
H NMR (300 MHz, CDCl ): d = 7.44 (m, 2 H), 7.94 (d, J = 6.0 Hz,
3
1
H), 8.47 (d, J = 9 Hz, 1 H).
1
3
C NMR (75 MHz, CDCl ): d = 128.84, 126.52, 123.37, 118.82.
3
MS: m/z (%) = 136 (100), 108 (80), 82 (60), 69 (51).
(8) Filimonov, V. D.; Trusova, M. E.; Postnikov, P. S.;
Krasnokutskaya, E. A.; Lee, Y. M.; Hwang, H. Y.; Kim, H.;
Chi, K.-W. Org. Lett. 2008, 10, 3961.
Acknowledgment
(
9) (a) Caldarelli, M.; Baxendale, I. R.; Ley, S. V. Green Chem.
000, 2, 43. (b) Merrington, J.; James, M.; Bradley, M.
Chem. Commun. 2002, 140.
2
This work was supported by the Russian Foundation for Basic Re-
search (project no. 09-03-99019), the Russian Federal programs GC
P1296, GC P33, GC 16.512.11.2127, and the World Class Univer-
sity program (R33-2008-10003) of the National Research Founda-
tion in Republic of Korea.
(
(
10) For several examples, the resulting diazonium tosylates can
be partially isolated from the aqueous solution by extraction
with ethyl acetate, followed by pouring the organic solution
in diethyl ether. Properties and spectral data of these salts
were identical to those previously obtained by diazotization
8
in acetic acid.
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Synthesis 2011, No. 13, 2154–2158 © Thieme Stuttgart · New York