One-pot preparations of diaryliodonium bromides from iodoarenes and arenes, with sodium perborate as the oxidant

Article abstract of DOI:10.3390/61100875

This paper reports a one-pot synthesis of the title bromides from both activated and deactivated iodoarenes which are first oxidized with anhydrous NaBO₃·H₂O/Ac₂O/conc.H₂SO ₄ liquid mixtures, then coupled in situ with benzene and activated arenes and, finally, precipitated out with a KBr solution; this method is easy, cheap, safe and fairly effective.

Full text of DOI:10.3390/61100875

Molecules 2001, 6, 875-880
molecules
ISSN 1420-3049
http://www.mdpi.org
One-Pot Preparations of Diaryliodonium Bromides from
Iodoarenes and Arenes, with Sodium Perborate as the Oxidant†
Anna Kryska and Lech Skulski*
Chair and Laboratory of Organic Chemistry, Faculty of Pharmacy, Medical University, Banacha 1, PL
02-097 Warsaw, Poland.
†
This paper was presented at the Fifth Electronic Conference on Synthetic Organic Chemistry
(ECSOC-5), September 1-30, 2001 (Paper A0007).
* Author to whom correspondence should be addressed; Tel/Fax: +48(22)8226843; e-mail:
lskulski@farm.amwaw.edu.pl
Received: 27 September 2001; in revised form 11 October 2001 / Accepted: 12 October 2001 /
Published: 31 October 2001
__________________________________________________________________________________
Abstract: This paper reports a one-pot synthesis of the title bromides from both activated
and deactivated iodoarenes which are first oxidized with anhydrous
NaBO3·H2O/Ac2O/conc.H2SO4 liquid mixtures, then coupled in situ with benzene and
activated arenes and, finally, precipitated out with a KBr solution; this method is easy,
cheap, safe and fairly effective.
Keywords: diaryliodonium bromides, iodoarenes, arenes, sodium perborate as oxidant
__________________________________________________________________________________
Introduction
Symmetric and unsymmetric diaryliodonium salts, Ar2I+X- and Ar(Ar')I+X-, represent an important
class of aromatic iodine(III) derivatives. They are used in organic synthesis mostly as arylating
reagents for a large variety of organic and inorganic nucleophiles. Some of them display a biological
activity or photochemical properties, hence they are widely used as efficient catalysts for radiation
initiated polymerisation. Generally, their reactivity is less pronounced than that of other hypervalent

Molecules 2001, 6
876
iodine(III) compounds. They are solid compounds, mostly stable towards heat (particularly those with
substantially nonnucleophilic counterions), oxygen, and humidity; they are mildly light-sensitive and
should be stored in the dark, without refrigeration [1].
Indeed, there a multitude of different published methods for their preparation are available [1], and
the relevant literature is still expanding nowadays with dislosures of some novel and possibly better
methods [2]. In our opinion, some of these methods are rather costly and/or too complicated to be
easily adopted in "ordinary" organic laboratories – but it is still possible and desirable to devise some
new preparative procedures, which would be easy, cheap, safe, and effective. We hope that a novel
method reported in this paper may fulfil, at least in part, these expectations.
Results and Discussion
In 1995 we reported [3] a one-pot ("short-cut") synthesis of sparingly soluble diaryliodonium
bromides (and iodides) from various iodoarenes, ArI, previously oxidized with anhydrous
CrO3/AcOH/Ac2O/conc. H2SO4 systems to form soluble iodine(III) intermediates, ArISO4 or
ArI(OSO3H)2 (not isolated), then coupled in situ with benzene and activated arenes/heteroarenes
(Ar'H) and, finally, precipitated out with excess aqueous KBr (or KI) solutions. The title bromides
were obtained in 20-88% crude yields (for more information see Ref. [3]). This method was easier and
shorter then many earlier methods [1], hence it was later often used in our laboratory [4-6], and
elsewhere [7].
We also reported [3, 5] the very simple and effective oxidative metatheses in the crude iodonium
bromides, iodides and chlorides into the corresponding pure tetrafluoroborates, tosylates, triflates,
trifluoroacetates, etc.; such diaryliodonium salts with substantially nonnucleophilic counterions are the
best arylating reagents [1]. However, there are some important, inherent limitations in the application
of our short-cut method [3]. Only iodobenzene, haloiodobenzenes, and iodoarenes substituted with
electron-withdrawing groups may effectively be applied to form the final iodonium bromides (or
iodides). 4-Iodotoluene coupled oxidatively with benzene gave 4-MeC6H4(Ph)I+Br- in only 20% crude
yield, whereas iodoanisoles and iodoacetanilides were oxidatively cleaved by CrO3 in acidic medium,
hence their oxidative coupling with activated arenes was not possible. Thus, we have been looking for
some novel and effective one-pot method, which would also be applicable for iodoarenes substituted
with electron-donating groups. In fact, we have increasingly been interested in the mild and selective
oxidative properties of sodium perborate (which is purchased either as "monohydrate" or
"tetrahydrate" at a low price) widely used in chemical laboratories or in industry. It may be considered
as a "dry carrier" of the hazardous and unstable hydrogen peroxide, is easy to handle, safe, and stable
at room temperature [8]. Therefore, we have decided to use NaBO3·H2O as the oxidant of choice,
because it is more soluble in acetic anhydride than NaBO3·4H2O. We know from our earlier work that
water, due to its high hydration power, diminishes the oxidizing activity of inorganic (and organic)
oxidants.
McKillop and Kemp [9] oxidized thirteen ArI (also those substituted with electron-donating
groups!) to the corresponding ArI(OAc)2 with NaBO3·4H2O (used in 900% excess) in a very large
volume of glacial acetic acid within 4-8 hours, at 40-50oC. After recrystallizations, they obtained the

Molecules 2001, 6
877
purified products in 66-80% yields. When we used acetic anhydride as the solvent of choice and
NaBO3·H2O as the oxidant, which allowed to lower considerably an excess of the oxidant applied to
only 200% as well as the volume of the solvent applied, we obtained five 4-XC6H4I(OAc)2 (X = H, F,
Br, Cl, MeO) as well as 2-MeOC6H4I(OAc)2 in 60-87% crude yields; after repeated recrystallizations,
we obtained the purified products [10]. This preliminary work opened up a new way to develop the
title one-pot method. We have also observed that a preliminary period of stirring NaBO3·H2O with
o
acetic anhydride at 30 C (preferably within 90 min) enhances considerably the oxidizing activity of
this solution. Recently, Indian chemists [11] have observed the generation of peracetic acid on aging
of NaBO3·4H2O solutions in glacial acetic acid, confirmed by chemical tests.
The essence of our novel method is given in the three equations below; for all preparative details
see Experimental.
(1) ArI + NaBO3·H2O + 2Ac2O +2H2SO4 → ArI(OSO3H)2 + [NaBO2] + 4AcOH
-
(2) ArI(OSO3H)2 (not isolated) + Ar'H (400% excess) → Ar(Ar')I+HSO4 + H2SO4
-
(3) Ar(Ar')I+HSO4 (not isolated) + aq. KBr (in excess) → ↓Ar(Ar')I+Br- + KHSO4
Small samples of the crude bromides were quickly [3] recrystallized from MeOH to give the pure
analytical samples. Their melting points agreed well with the literature data [3, 12], and their structures
were confirmed by correct elemental analyses (Table 1) as well as 1H-NMR spectra (not shown here);
the spectra (in DMSO-d6/DDS) displayed the sharp singlets located at ca. 2.20, 2.45, 2.75, and 4.20
ppm, characteristic of the COCH3, 4-CH3Ar, 2- and 2,6-CH3Ar, or 4-OCH3 groups, respectively, as
well as composite multiplets characteristic of the aromatic protons (the thoroughful integrations
disclosed the total numbers of aromatic protons related to the aforesaid three-proton singlets); cf. our
former papers [3, 5].
Conclusions
In this paper we present a novel one-pot method for easy and effective preparation of a number of
diaryliodonium bromides (Table 1). They were produced from both activated and deactivated
iodoarenes and 2-iodothiophene, which next were oxidatively coupled with activated arenes, in
appropriate anhydrous NaBO3·H2O/Ac2O/conc. H2SO4 mixtures. Next, the iodonium bromides were
precipitated out by the addition of excess KBr solution to the resulting final reaction mixtures. After
their collection, washing, and air-drying, the final products were obtained in 23-98% crude yields;
only small samples were purified and analysed. Sodium perborate monohydrate used as the oxidant is
cheap, safe and effective; no toxic residues were left after the reactions - in a strong contrast to our
former method [3].
Experimental
General
All iodoarenes, arenes, solvents as well as inorganic reagents were pure commercial products. The
melting points of the purified diaryloiodonium bromides (Table 1) are uncorrected, and were measured

Molecules 2001, 6
878
as follows. Since they depend on the duration of heating, after an approximate mp was taken in an
o
open capillary tube, a new sample was introduced about 10 C below this point, and the temperature
o
1
was then raised at a rate of 4-5 C per minute. H-NMR solution spectra (not shown here) were
recorded with a Tesla (100 MHz) spectrometer. Microanalyses were carried out at the Institute of
Organic Chemistry, the Polish Academy of Sciences, Warsaw.
One-Pot Preparations of Diaryliodonium Bromides
o
NaBO3·H2O (37.5 mmol) was suspended in Ac2O (17 mL), and this mixture was stirred at 30 C
for 90 min. An appropriate iodoarene (12.5 mmol) was then added, the mixture was stirred at 40 oC for
1.5 h, and at that point benzene or an appropriate activated arene (5 × 12.5 mmol) was added, and the
o
mixture was cooled to 5-10 C. Conc. (98%) H2SO4 (2.5 mL) was slowly added dropwise, with
o
stirring, while keeping the temperature below 15 C. Next, the mixtures were stirred, at appropriate
o
temperature (10-30 C) for a given time (4-6 h, but with benzene 48 h; see Table 1 for details). The
final reaction mixtures were poured into cold water (150 mL) and stirred for 0.5-1 h. The unreacted
organic substrates were extracted with Et2O (2 × 20 mL), and the ethereal extracts were discarded. The
aqueous layers, if dark-coloured, were decolourized with charcoal while boiling. To the cooled
filtrates, excess aq. KBr (6 g KBr in 30 mL water) was added with stirring. After 1-2 h, the precipitates
were collected, washed well with water, acetone, and Et2O, air-dried, and weighed to give the
iodonium bromides in 23-98% crude yields (Table 1). Note. When the iodoarenes and/or arenes used
were solid compounds, which rendered the stirring more difficult, then an additional amount of Ac2O
(5-10 mL) was added to the reaction mixtures, prior to the addition of conc. H2SO4.
Table 1. Preparative Details, Crude Yields, and Melting Points of the Purified
Diaryliodonium Bromides 1-24 as well as their Elemental Analyses
Substrates
ArI, Ar'H
PhI, PhH
Product
Ar(Ar')I+Br-
Time [h]/
Temp. [oC]a
48/30
CrudeYield Mp [oC] Analyses [% I]
[%]
Calcd/Found
Diphenyliodonium bromide (1)
51
246-247
199-200
35.15/35.3
PhI, PhMe
4-Methyldiphenyliodonium bromide
5/15
5/15
5/15
5/25
5/15
65
82
91
30
55
33.83/33.6
31.48/31.6
32.45/32.4
30.35/30.5
34.57/34.9
(2)
PhI,
2,4,6-Trimethyldiphenyliodonium
166-167
211-212
202-203
206-207
Mesitylene
PhI, PhOMe
bromide (3)
4-Methoxydiphenyliodonium bromide
(4)
PhI, PhNHAc 4-Acetylaminodiphenyliodonium
bromide (5)
PhI, Thiophene Phenyl(2-thienyl)iodonium bromide
(6)

Molecules 2001, 6
879
2-I-Thiophene, 4-Methoxy-2-methylphenyl(2-
3-MeC6H4OMe thienyl)iodonium bromide (7)
2-I-Thiophene, 2,2'-Dithienyliodonium bromide (8)
Thiophene
6/15
6/15
6/15
6/15
6/15
5/15
5/15
5/15
5/15
5/15
5/10
5/15
5/15
23
30
50
55
70
70
48
50
50
45
40
55
25
154-155
183-184
200-201
171-172
194-195
223-224
178-179
210-211
193-194
198-200
206-207
185-186
201-202
32.19/32.4
34.01/34.4
31.22/31.5
31.22/31.5
31.22/31.4
30.04/29.9
30.04/30.0
30.04/30.1
28.32/27.9
28.32/27.9
28.32/28.6
29.96/30.1
29.00/29.4
2-MeC6H4I,
PhOMe
4-Methoxy-2'-methyldiphenyl-
iodonium bromide (9)
3-MeC6H4I,
PhOMe
4-Methoxy-3'-methyldiphenyl-
iodonium bromide (10)
4-MeC6H4I,
PhOMe
4-Methoxy-4'-methyldiphenyl-
iodonium bromide (11)
2-MeOC6H4I, 2,4'-Dimethoxydiphenyliodonium
PhOMe bromide (12)
3-MeOC6H4I, 3,4'-Dimethoxydiphenyliodonium
PhOMe bromide (13)
4-MeOC6H4I, 4,4'-Dimethoxydiphenyliodonium
PhOMe bromide (14)
2-AcNHC6H4I, 2-Acetylamino-4'-methoxydiphenyl-
PhOMe iodonium bromide (15)
3-AcNHC6H4I, 3-Acetylamino-4'-methoxydiphenyl-
PhOMe iodonium bromide (16)
4-AcNHC6H4I, 4-Acetylamino-4'-methoxydiphenyl-
PhOMe
iodonium bromide (17)
4-ClC6H4I,
1,3-Xylene
4-ClC6H4I,
Mesitylene
4-ClC6H4I,
PhOMe
4-Chloro-2',4'-dimethyldiphenyl-
iodonium bromide (18)
4-Chloro-2',4',6'-trimethyl-
diphenyliodonium bromide (19)
4-Chloro-4'-methoxydiphenyl-
iodonium bromide (20)
6/15
5/15
87
96
205-206
167-168
29.83/30.1
29.21/29.0
4-AcC6H4I,
PhOMe
4-Acetyl-4'-methoxydiphenyl-
iodonium bromide (21)
2-O2NC6H4I,
PhOMe
4-Methoxy-2'-nitrodiphenyliodonium
bromide (22)
6/15
4/15
4/15
96
98
55
185-186
175-176
157-158
29.10/29.2
29.10/28.9
29.10/29.0
3-O2NC6H4I,
PhOMe
4-Methoxy-3'-nitrodiphenyliodonium
bromide (23)
4-O2NC6H4I,
PhOMe
4-Methoxy-4'-nitrodiphenyliodonium
bromide (24)
a Time and temperature of the acidic coupling reaction between a prior oxidized ArI and an appropriate
Ar'H.

Molecules 2001, 6
880
References and Notes
1. (a) Olah, G. A. Halonium Ions. Wiley: New York, 1975; (b) Koser, G. F. In The Chemistry of
Functional Groups. Suppl. D Patai, S.; Rappoport, Z., Eds.; Wiley-Interscience: Chichester, 1983,
Chapter 25; (c) Varvoglis, A. The Organic Chemistry of Polycoordinated Iodine. VCH: Weinheim,
1992; (d) Koser, G. F. In The Chemistry of Halides, Pseudo-Halides and Azides, Suppl. D2 Patai,
S.; Rappoport, Z., Eds.; Wiley-Interscience: Chichester, 1995, Chapter 21; (e) Stang, P. J.;
Zhdankin, V. V. Chem. Rev. 1996, 96, 1123; (f) Varvoglis, A. Hypervalent Iodine in Organic
Synthesis Academic Press: San Diego, 1997.
2. (a) Ochiai, M.; Toyonari, M.; Sueda, T.; Kitagawa, Y. Tetrahedron. Lett. 1996, 37, 8421; (b) Shah,
A.; Pike, V. W.; Widdowson, D. A. J. Chem. Soc., Perkin Trans. 1, 1997, 2463; (c) Roh, K. R.;
Kim, J. Y.; Kim, Y. H. Chem. Lett. 1998, 1095; (d) Ochiai, M.; Yutaka, Y.; Takayama, N.;
Takaoka, Y.; Shiro, M. J. Am. Chem. Soc. 1999, 121, 9233; (e) Kitamura, T.; Wakimoto, I.;
Nakamura, T.; Fujiwara, Y. Org. Lett. 1999, 253; (f) Kitamura, T.; Yamane, M.; Inoue, K.;
Todaka, M.; Fukatsu, N.; Meng, Z.; Fujiwara, Y. J. Am. Chem. Soc. 1999, 121, 11674; (g) Pike, V.
W.; Butt, F.; Shah, A.; Widdowson, D. A. J. Chem. Soc., Perkin Trans. 1 1999, 245; (h) Kitamura,
T.; Meng, Z.; Fujiwara, Y. Tetrahedron. Lett. 2000, 41, 6611; (i) Carrol, M. A.; Pike, V. M.;
Widdowson, D. A. Tetrahedron Lett. 2000, 41, 5393; (j) Grushin, V. V. Chem. Soc. Rev. 2000, 29,
315; (k) Peacock, M. J.; Pletcher, D. Tetrahedron Lett. 2000, 41, 8995.
3. Kazmierczak, P.; Skulski, L. Synthesis, 1995, 1027.
4. Farhan, A. N.; Skulski, L. Pol. J. Chem. (a) 1995, 69, 1663; (b) 1996, 70, 211; (c) 1997, 71, 1236.
5. Kazmierczak, P.; Skulski, L. Bull. Chem. Soc. Jpn. 1997, 70, 219.
6. Skulski, L.; Wroczynski, P. Bull. Pol. Acad. Sci., Chem. 1999, 47, 231.
7. Zhou, T.; Chen, Z. – C. J. Chem. Res., Synop. 2001, 153, see p 154.
8. (a) Muzzart, J. Synthesis 1995, 1325; (b) McKillop, A.; Sanderson, W. R. Tetrahedron 1995, 51,
6145; (c) McKillop, A.; Sanderson, W. R. J. Chem. Soc., Perkin Trans. 1 2000, 471.
9. McKillop, A.; Kemp, D. Tetrahedron 1989, 45, 3299.
10. Skulski, L. Molecules, 2000, 5, 1331, pp 1353-1354 and 1361. Avail. at URL:
http://www.mdpi.org/molecules/papers/51201331.pdf
11. Karunakaran, C.; Kamalan, R. Eur. J. Org. Chem. 2000, 3261.
12. (a) Beringer, F. M.; Gindler, E. M. Iodine Abstr. Rev. 1956, 3, 1; Drexler, M.;Gindler, E. M.;
Lumpkin, C. C. J. Am. Chem. Soc. 1953, 75, 2705; (c) Beringer, F. M.; Bachofner, H. E.; Falk, R.
A.; Leff, M. J. Am. Chem. Soc. 1958, 80, 4279; (d) Beringer, F. M.; Karniol, M.; Lillien, I.;
Masullo, G.; Mausner, M.; Sommer, E. J. Am. Chem. Soc. 1959, 81, 342.
Sample availability: Samples of crude compounds 1-24 are available from the authors. Samples of
pure compounds 4, 9-11, 14-16 are available from MDPI.
© 2001 by MDPI (http://www.mdpi.org). Reproduction is permitted for noncommercial purposes.