Combination of sulfite anion and Phase Transfer Catalysts for green cyclotrimerization of aryl isocyanates

Article abstract of DOI:10.1081/SCC-200048951

The catalytic cyclotrimerization of aryl and alkyl isocyanates by the novel combination catalysts of sulfite ion and Phase Transfer Catalysts (PTCs), as selective anionic catalysts, has been investigated. The use of phase transfer catalyst features the ca

Full text of DOI:10.1081/SCC-200048951

This article was downloaded by: [The University Of Melbourne Libraries]
On: 09 October 2014, At: 21:29
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic
Organic Chemistry
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Combination of Sulfite Anion
and Phase Transfer Catalysts
for Green Cyclotrimerization of
Aryl Isocyanates
a b
a
Mohammad G. Dekamin
, Shadpour Mallakpour
a
&
a
Maryam Ghassemi
Organic Polymer Chemistry Research Laboratory,
College of Chemistry , Isfahan University of
Technology , Isfahan, IR, Iran
b
Department of Chemistry , Iran University of
Science and Technology , Tehran, 16844, Iran
Published online: 28 Jul 2007.
To cite this article: Mohammad G. Dekamin , Shadpour Mallakpour & Maryam
Ghassemi (2005) Combination of Sulfite Anion and Phase Transfer Catalysts for Green
Cyclotrimerization of Aryl Isocyanates, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 35:3, 427-434, DOI:
10.1081/SCC-200048951
To link to this article: http://dx.doi.org/10.1081/SCC-200048951
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no

representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

w
Synthetic Communications , 35: 427–434, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048951
Combination of Sulfite Anion and Phase
Transfer Catalysts for Green
Cyclotrimerization of Aryl Isocyanates
†
Mohammad G. Dekamin, Shadpour Mallakpour,
and Maryam Ghassemi
Organic Polymer Chemistry Research Laboratory, College of Chemistry,
Isfahan University of Technology, Isfahan, IR Iran
Abstract: The catalytic cyclotrimerization of aryl and alkyl isocyanates by the novel
combination catalysts of sulfite ion and Phase Transfer Catalysts (PTCs), as
selective anionic catalysts, has been investigated. The use of phase transfer catalyst
features the catalytic potency of sulfite anion and promotes the reaction in green con-
ditions. Diverse aryl derivatives have been involved in the reaction condition giving
corresponding isocyanurates in good to excellent yields.
Keywords: Isocyanates, sulfite anion, phase transfer catalysis, cyclisation, triazines,
green chemistry
The synthesis of the aromatic heterocyclic structure of 1,3,5-triazine-2,4,6
(
1H,3H,5H)trione, known as isocyanurate, has received continued attention.
Thanks to its thermal and chemical stability, this structure improves thermal
and chemical resistance, flame retardation and film-forming characteristics
[
1–5]
of polyurethanes and polyureas as coating materials.
rates have also been employed as activators for the continuous anionic
Triaryl isocyanu-
[
polymerization of 1-caprolactam to nylon-6 or insecticides. Recently
the isocyanurate structure have been investigated in nonlinear optical,
4]
[6]
[7]
Received in Poland September 19, 2004
†
Previous Name: Shadpour E. Mallakpour
Address correspondence to Mohammad G. Dekamin, Department of Chemistry,
Iran University of Science and Technology, Tehran, 16844, Iran. E-mail:
mdekamin@yahoo.com

428
M. G. Dekamin, S. Mallakpour, and M. Ghassemi
[
8]
[9]
enantiomeric discrimination and low-toxicity mammalian drug delivery
applications.
Many catalysts have already been used for cyclotrimerization reaction of iso-
cyanates, as a general method for construction of the isocyanurate ring, since the
pioneering works by Hoffman and Michael in the last decades of nineteenth
[
5,10,11]
century.
as metal alkoxides,
The introduced catalysts fall in five categories: a) anionic such
[1,3,5]
[
10,11]
[2]
various metal salts of carboxylic acids,
salts; b) neutral Lewis bases such as proazaphosphatrane and
fluoride
[12,13]
and cyanate
quasi-azaphosphatrane, phosphines and tertiary amines;
[4]
[14]
c) organometal-
which most of them rely on tin compounds; d) Lewis acids and
[
15–20]
lics
weak Bronsted acids such as AlCl3 and phenols or alcohols; e) combination
[21]
[22]
[23]
catalysts such as pyridine and epoxides, 2-tributylstannylpropanol and quatern-
[24]
[25]
ary ammonium halides, ethyl alcohol and N-methylmorpholine and carbox-
[1,3,5]
ylate salts along with quaternary ammonium salt.
Owing to the industrial and commercial importance of the catalytic
aspects of the reaction, the search for new catalysts and green conditions
[
4,17,18,20,24,26]
has been already continued.
the selective catalytic activity of sodium or potassium salts of piperidine-
We have recently demonstrated
[
27]
[28]
dithiocarbamate and nitrite,
saccharin
sodium p-toluenesulfinate,
as new anionic catalysts, alone or in the presence of tetrabuty-
and sodium
[29]
lammonium iodide (TBAI) in solvent-free condition. In continuation of our
interest in this field to develop nontoxic, nonmetallic, and readily available
catalysts which work in solvent-free condition and similarity of sulfite to p-
toluenesulfinate, here we wish to report an easy method for preparation of
aryl isocyanurates catalyzed by the readily available sulfite anion.
When a mixture containing 0.33mol% of potassium sulfite, 0.66mol% of
tetrabutylammonium bromide (TBAB) and phenyl isocyanate 1a was heated at
1
dified after 13min (Table 1, entry 2). However, K SO alone does not show any
208C, the product 4a appeared as a solid mass after 4 min and the mixture soli-
2
3
catalytic activity in the same condition after 24h (Scheme 1).
Among tetrabutylammonium halides only fluoride has catalytic activity
[
2,24]
for the reaction,
therefore, TBAB could improve the catalytic activity
of sulfite anion by increasing its solubility and nucleophilicity in organic
phase. Separation of the unreacted substrate and catalyst from the product
could be achieved by simply triturating and then filtering of the crushed
reaction mixture by dry ether and water, respectively (see the Experimental
section). The reaction conditions were optimized with phenyl isocyanate, as
a model compound, at various concentrations of sulfite anion and TBAB or
[2]
temperatures. In all cases, TLC comparison with an authentic sample
reveals that triphenyl isocyanurate is the exclusive product of the reaction,
free of any undesirable products such as corresponding dimer, diphenyl diaze-
[
2,4,23–25]
tidinedione, or diphenyl carbodiimide.
The results are summarized in
Table 1. Therefore, 0.33 mol% of K SO and TBAB at 708C was selected as
2
3
optimal condition (Table 1, entry 9).

Green Cyclotrimerization of Aryl Isocyanates
429
Table 1. The effect of various mole percents of potassium sulfite 2, TBAB 3, and
temperatures on the cyclotrimerization of phenyl isocyanate 1a
TBAB
mol%
Temperature
(8C)
Time
(min)
a
Entry
2 mol%
Yield (%)
1
2
3
4
5
6
7
8
9
0.33
0.33
0.33
0.33
0.33
0.16
0.50
0.66
0.33
0.33
0.33
0.33
0.33
0.66
0.66
0.66
0.66
0.66
0.33
1.0
140
120
95
70
55
70
70
70
70
70
rt
12
13
69
70
20
30
73
84
41
63
85
75
14
12
81
74
1.32
0.33
0.16
0.33
0.33
0.66
24
37
86
79
1
1
1
1
0
1
1
2
10 h
24 h
24 h
76
Trace
80
b
b
70
70
a
b
Isolated yield.
Sodium sulfite as catalyst.
Other phase transfer catalysts possessing the required character-
[2,28,29]
istics
were examined at optimized condition. The results have been
summarized in Table 2. Increasing the size of anion in PTC, used as TBAI,
slows down the reaction (Table 2, entry 1). On the other hand, both increasing
and decreasing the size of tetraalkylammonium part of PTC has the same
effect on the reaction rate (Table 2, entries 2, 3). Interestingly, higher yield
was observed with bulkier cetyltrimethylammonium bromide (CTAB).
2
2
2
The results also showed that anions such as BF , ClO , and HSO alone
have no catalytic activity while their counter ion is the same with the TBAB
4
4
4
Scheme 1.

430
M. G. Dekamin, S. Mallakpour, and M. Ghassemi
Table 2. Effect of different combinations of anions and PTCs 3 on
cyclotrimerization of phenyl isocyanate 1a at optimized condition
a
Entry
Anion
PTC 3
Time (h)
Yield (%)
1
2
3
4
5
K
2
SO
K SO
3
3
3
3
3
TBAI
TEAB
1.05
0.78
0.63
0.38
0.38
75
71
92
84
76
b
c
2
K
K
2
SO
SO
CTAB
Bu
Bu NClO
2
NBF
4 4
K SO
2
4
4
a
Isolated yield.
b
Tetraethylammonium bromide.
Cetyltrimethylammonium bromide.
c
even after 24 h. By adding equivalent amount of sulfite anion, only Bu NBF
4
4
and Bu NClO display its catalytic activity similar to that of TBAB (Table 2,
4
4
entries 4, 5).
Development of the optimized conditions to other derivatives of aryl and
alkyl isocyanate and phenyl isothiocyanate gave corresponding trimer of aryl
ones in good to excellent yields within a short reaction times. Table 3 summar-
izes the results. Aryl isocyanates with electron withdrawing groups react faster
than ones containing donating groups. This order of reactivity demonstrates
another advantage of our combination system over many of the so far intro-
[4]
duced catalysts which fail to trimerize even 4-methylphenyl isocyanate.
In conclusion, sulfite anion in combination with phase transfer catalysts
has been introduced as a novel combination system for multicomponent cyclo-
trimeriztion reaction of aryl isocyanates. Also sulfite anion which is inexpen-
sive and readily available in the form of its potassium salt, dissolves in water
and its separation from the product could be accomplished by simple triturat-
ing of the reaction mixture by water. On the other hand, application of phase
transfer catalysts reduces or eliminates energy, time, and toxic solvents (such
[
4,23]
as benzene, pyridine, DMSO, and DMF)
requirements of the reaction
while featuring the catalytic potency of sulfite anion as an efficient and
selective catalyst. These situations lead the reaction conditions to be
[30–33]
green.
EXPERIMENTAL
General Methods
Melting points are uncorrected. FT IR spectra were recorded as KBr pellets.
1
13
H NMR and C NMR spectra were obtained on a 500 MHz spectrometer
and referenced to TMS or residual CDCl . Analytical TLC was carried out
3

Green Cyclotrimerization of Aryl Isocyanates
431
Table 3. Cyclotrimerization of aryl and alkyl isocyanates 1 to the corresponding iso-
cyanurates 4 at optimized condition
Time Product
(min)
Isolated
yield (%)
a
Entry
1
Isocyanate 1
4
Mp 8C (Lit.)
[
4]
33
4a
81
92
91
280–2 (279)
2
3
25
7
4b
4c
317–8
[
25]
(
318)
277–9
[
25]
(
279)
4
5
6
6
225
80
4d
4e
4f
85
90
86
348–9
[
25]
(
350)
[
4]
261–2 (261)
278–80
a
All of the products, except compound 4f, are known[4,23,25,24] and the isolated
1
products gave IR and H NMR spectra in agreement with their structures.
Alkyl and aryl carboxylate esters of triphenyl isocyanurate have been prepared only
by the reaction of corresponding trimethylsilyl ether isocyanurate, as a reactive isocya-
nurate, with corresponding acid chlorides catalyzed by cesium fluoride generating tri-
methylchlorosilane. In this work, novel tris-(4-acetoxyphenyl) isocyanurate 4f has been
synthesized by starting from its isocyanate in high yield (Table 3, entry 6). On the other
hand, the combination catalyst has no catalytic activity for alkyl isocyantes and phenyl
isothiocyanate (1g–1i) which most of catalysts fail to trimerize these substrates.
using Fluka aluminium-backed 0.2 mm silica gel 60 F-254 plates. The end of
reactions were determined on solidification of the reaction mixture in the case
of aryl isocyanates or substantial condensation of alkyl ones. Dry ether was
distilled freshly from ether on sodium and benzophenone. K SO , Na SO ,
2
3
2
3
all anionic catalysts and PTCs were dried under reduced pressure at 708C
for 2 h prior to use and then kept in a dessicator. Except 4-nitrophenyl, 4-meth-
oxyphenyl and 4-acetoxyphenyl isocyanate which prepared by known litera-
[34,35]
ture procedures
from 4-nitrobenzoyl chloride, 4-methoxybenzoic acid
and 4-hydroxybenzoic acid respectively, all substrates were used as
received from Merck. All cyclotrimerization reaction were carried out using
carefully oven-dried glassware and protected from the environment
moisture by a CaCl tube. All products have been crystallized from EtOH
2
or EtOH/EtoAc, giving satisfactory spectroscopic data compared with those

432
M. G. Dekamin, S. Mallakpour, and M. Ghassemi
[
4,23–25]
of authentic samples,
and their yields refer to isolated pure products.
Caution: For safety reasons, all the experiments must be performed in an
efficient fume hood and necessary precautions considered in order to avoid
any contact with substrates during the operation.
Typical Isocyanate Cyclotrimerization
A mixture of 1f (0.500 g, 2.82 mmol), K SO (0.0015 g, 9.31 mmol) and
3
2
TBAB (0.0030 g, 9.31 mmol) in a 20 mL flask attached to a condenser was
heated at 708C in an oil bath. After solidification of the reaction mixture,
2
mL dry ether was added and refluxed for 10 min in the oil bath. The
reaction mixture then cooled to room temperature and additional 15 mL dry
ether was added after complete crushing the reaction mixture. The suspension
was stirred for 10 min and filtered by a Buchner funnel to yield a powdery
crude reaction product which in most cases is sufficiently pure. Further puri-
fication by crystallization from EtOH/EtOAc gave 0.43 g (86%) of 1,3,5-tris-
(
4-acetoxyphenyl) isocyanurate (4f) as white crystals. Mp ¼ 278–808C; IR
2
1
1
KBr pellet) 2968, 2935, 1762, 1709, 1601, 1507, 1409, 1196 cm ; H
(
NMR (500 MHz, CDCl ) d 7.44- 7.42 (d, J ¼ 8.74 Hz, 6 H), 7.30- 7.27
3
1
3
(
d, J ¼ 8.74 Hz, 6 H), 2.34 (s, 9 H); C NMR (125 MHz, CDCl ) d 169.25,
3
1
51.52, 148.88, 131.17, 129.96, 122.88, 21.54; MS (EI) for C H N O
27 21 3 9
(M) calcd. 531.43, found 531.42.
ACKNOWLEDGMENT
We thank the Research Deputy of Isfahan University of Technology (IUT), IR
Iran for financial support of the project. Further financial support from Center
of Excellency in Chemistry Research (IUT) is also gratefully acknowledged.
REFERENCES
1
2
. Modesti, M.; Lorenzetti, A. An experimental method for evaluating isocyanate
conversion and trimer formation in polyisocyante-polyurethane foams. Eur.
Polym. J. 2001, 37, 949–954.
. Nambu, Y.; Endo, T. Synthesis of novel aromatic isocyanurates by the flouride-
catalyzed selective trimerization of isocyanates. J. Org. Chem. 1993, 58 (7),
1932–1934.
3
. Ni, H.; Aaserud, D. J.; Simonsick, W. J., Jr.; Soucek, M. D. Preparation and charac-
terization of alkoxysilane functionalized isocyanurates. Polymer. 2000, 41, 57–71.
. Tang, J.; Mohan, T.; Verkade, J. G. Selective and efficient syntheses of
perhydro-1,3,5-triazine-2,4,6-triones and carbodimides from isocyanates using
4

Green Cyclotrimerization of Aryl Isocyanates
433
ZP(MeNCH
references cited there in.
3 2 2 3
CH CH ) N catalysts. J. Org. Chem. 1994, 59 (17), 4931–4938 and
5
. Wegener, G.; Brandt, M.; Duda, L.; Hofmann, J.; Klesczewski, B.; Koch, D.;
Kumpf, R. J.; Orzesek, H.; Pirkl, H. G.; Six, C.; Steinlein, C.; Weisbeck, M.
Trends in industrial catalysis in the polyurethane industry. Appl. Cat. A: Gen.
2001, 221, 303–335.
6
7
. Moehring, E.; Roessler, P. Insecticidal triazine-2,4-diones. Ger. Offen. 2,723,119,
December 7, 1978; Chem. Abstr., 1979, 90: 12666p.
. Thallapally, P. K.; Chakraborty, K.; Carrell, H. L.; Kotha, S.; Desiraju, G. R. Shape
and size effect in the crystal structure of complexes of 1,3,5-trinitrobenzene with
some trigonal donors: The benzene-thiophene exchange rule. Tetrahedron. 2000,
56, 6721–6728.
8
9
. Sugimoto, H.; Yamane, Y.; Inoue, S. Enantiomeric discrimination by novel
optically active isocyanurates having peripheral amino units. Tetrahedron:
Assym. 2000, 11, 2067–2075.
. Murray, A. P.; Miller, M. J. The preparation of a fully differentiated “multiwar-
head” siderophore precursor. J. Org. Chem. 2003 (68), 191–194and references
cited there in.
1
0. Hoffman, A. W. Ber. 1870, 3, 765(See Richter, F.; Pedian, J.; Mertes, H.; Dieris,
C. G. Isocyanttrimerisate und Isocyanattrimerisatmischungen, dern Herstellung
und Verwendung. EP Patent 0,798,299, March 13, 1997).
1
1
1. Michael, A. Ber. 1888, 21, 411See Nambu and Endo, 1993).
2. Argabright, P. A.; Philips, B. L. The reaction of cyanate ion with organic
isocyantes. A new general synthesis of di- and trisubstituted isocyanurates. Tetra-
hedron Lett. 1968, 5033–5036.
1
3. Dubosclarard-Gottardi, C.; Caubere, P.; Fort, Y. New selective syntheses of
(meth)acrylic monomers: Isocyanates, isocyanurates, carbamates and ureas deriva-
tives. Tetrahedron 1995, 51, 2561–2572.
1
4. Taguchi, Y.; Shibuya, I.; Yasumoto, M.; Tsuchiya, T.; Yonemoto, K. The synthesis
of isocyanurates on the trimerisation of isocyanates under high pressure. Bull.
Chem. Soc. Jpn. 1990, 63 (12), 3486–3489.
1
1
1
5. Bloodworth, A. J.; Davies, A. G. Organometallic reactions. Part III. Trimerisation
of isocyanates by organotin alkoxides and oxides. J. Chem. Soc. 1965, 6858–6863.
6. Flamini, A.; Giuliani, A. M.; Poli, N. Catalytic activation of phenylisocyante by
3
Ti(bpy) . Tetrahedron Lett. 1987, 28 (19), 2169–2170.
7. Foley, S. R.; Zhou, Y.; Yap, G. P.A.; Richeson, D. S. Synthesis of
II
t
M [N(SiMe
sors: Active catalysts for phenyl isocyante cyclization. Inorg. Chem. 2000,
9 (5), 924–929.
3
)
2
][Me
3
SiNC( Bu)NSiMe
3
] (M ¼ Sn, Ge) from amidinate precur-
3
1
1
2
8. Montilla, F.; Clara, E.; Aviles, T.; Casimiro, T.; Ricardo, A. A.; Daponte, M. N.
Transition-metal-mediated activation of arylisocyantes in supercritical carbon
dioxide. J. Organomet. Chem. 2001, 626, 227–232.
9. Wakeshima, I.; Suzuki, H.; Kijima, I. The cyclic trimerization of isocyantes by
organotin tin(ii) compound containing Sn-O-C bonds. Bull. Chem. Soc. Jpn.
1975, 48 (3), 1069–1070.
0. Zhang, J.; Ruan, R.; Shao, Z.; Cai, R.; Weng, L.; Zhou, X. Insertion of carbodii-
mide into the Ln-C s-bond of organolanthanide complexes, synthesis, reaction,
t
Ln[ BuN-C( Bu)-
n
and characterization of organolanthanide amidinates (C
t
5
H
5
)
2
N Bu] (Ln ¼ Er, Gd, Y). Organometallics. 2002, 21 (7), 1420–1424.

434
M. G. Dekamin, S. Mallakpour, and M. Ghassemi
2
1. Dokunikhin, N. S.; Gaeva, L. A. Organic isocyanates V. Mechanism of transform-
ation of aryl isocyanates under the action of aluminum chloride. Zhur. Obshchei
Khim. 1959, 29, 297–301Chem. Abstr. 1959, 56, 21988b.
2
2. Schwetlick, K.; Noack, R. Kinetics and catalysis of consecutive isocyante
reactions. Formation of carbamates, allophonates and isocyanurates. J. Chem.
Soc. Perkin Trans. 1995 (2), 395–402.
23. Jones, J. I.; Savil, N. G. The polymerisation of aromatic isocyanates. J. Chem. Soc.
1957, 4392–4394.
2
4. Marc, F.; Saux, A.; Ratier, M.; Duboudin, J. G.; Daude, G. Quaternary ammonium
halides/2-tributylstannylpropanol: An efficient cyclotrimerization catalyst system
for aromatic isocyanurate synthesis. Polymer 1994, 35 (23), 5146–5147.
5. Kogon, I. C. New reactions of phenyl isocyante and ethyl alcohol. J. Am. Chem.
Soc. 1956, 78, 4911–4914.
2
2
6. Verkade, J. G.; Tang, J. Method for synthesis of triarylisocyanurates from aryl iso-
cyanates using triazaphosphatrane catalysts. US Patent. 5,260,436, November 9,
1993; Chem. Abstr., 1994, 120, 218836v.
2
2
7. Khajavi, M. S.; Dekamin, M. G.; Hazarkhani, H. Solvent-Free cyclotrimerization
of isocyanates by sodium or potassium piperidinedithiocarbamate or nitrite under
conventional or microwave heating: Preparation of aryl and alkyl isocyanurates.
J. Chem. Res. (S) 2000, 145–147.
8. Matloubi Moghaddam, F.; Dekamin, M. G.; Khajavi, M. S.; Jalili, S. Efficient and
selective trimerization of aryl and alkyl isocyanates catalyzed by sodium p-tolue-
nesulfinate in the presence of TBAI in a solvent-free condition. Bull. Chem. Soc.
Jpn. 2002, 75 (4), 851–852.
2
9. Matloubi Moghaddam, F.; Koozehgiri, G.; Dekamin, M. G. Solvent-free efficient
synthesis of symmetrical isocyanurates by a combination catalyst: Sodium
saccharin and tetrabutylammonium iodide. Monatsh. Chem. 2004, 135, 849–851.
0. Anastas, P. T.; Bartlett, L. B.; Kirchhof, M. M.; Williamson, T. C. The role of
catalysis in the design, development and implementation of green chemistry.
Catal. Today 2000, 55, 11–22.
3
3
3
1. Makosza, M. Phase-Transfer Catalysis. A general green methodology in organic
synthesis. Pure. Appl. Chem. 2000, 72 (7), 1399–1403.
2. Metzger, J. O. Organic reactions without organic solvents and oils and fats as
renewable raw materials for the chemical industry. Chemosphere. 2001, 43,
8
3–87.
3. Tanaka, K.; Toda, F. Solvent-free organic synthesis. Chem. Rev. 2000, 100,
025–1074.
4. Furniss, B. S.; Hannaford, A. J.; Rogers, V.; Smith, P. W.G.; Tatchell, A. R.
Aromatic compounds. In Vogel’ Textbook of Practical Organic Chemistry;
Longman Inc.: New York, 1986, pp. 831–832.
3
3
1
35. Reijendam, J. W.; Baardman, F. An improved method for the synthesis of acyl
azides. Synthesis 1973, 413–414.