A simple, two-step conversion of various iodoarenes to (diacetoxyiodo)arenes with chromium(VI) oxide as the oxidant

Article abstract of DOI:10.1055/s-1998-2223

Chromium(VI) oxide, an inexpensive and easily handled oxidant, dissolved in the anhydrous acetic acid/acetic anhydride/concentrated H₂SO₄ liquid system effectively oxidizes various iodoarenes ArI to the respective iodine(III) intermediates AxISO₄ and/or ArI(OSO₃H)₂. The resulting solutions were mixed with excess 20% aqueous ammonium acetate solution to give, after filtration and purification, (diacetoxyiodo)arenes ArI(OAc)₂ in 58-82% yields.

Full text of DOI:10.1055/s-1998-2223

SYNTHESIS
Deember 1998
1721
A Simple, Two-Step Conversion of Various Iodoarenes to (Diacetoxyiodo)arenes with
Chromium(VI) Oxide as the Oxidant†
PaweΩ Ka´zmierczak, Lech Skulski*
Chair and Laboratory of Organic Chemistry, Faculty of Pharmacy, Medical Academy, Banacha 1, PL 02-097 Warsaw, Poland
Fax +48(22)8231487
Received 18 March 1998; revised 9 May 1998
Abstract: Chromium(VI) oxide, an inexpensive and easily han-
dled oxidant, dissolved in the anhydrous acetic acid/acetic anhy-
dride/concentrated H2SO4 liquid system effectively oxidizes
iodoarenes ArI were immediately obtained (Equation 1).
various iodoarenes ArI to the respective iodine(III) intermediates
ArI(OSO3H)2 into excess aqueous Na2SO3 solution buff-
ered with (NH4)2CO3 to neutralize H2SO4, the respective
ArISO4 and/or ArI(OSO3H)2. The resulting solutions were mixed
with excess 20% aqueous ammonium acetate solution to give,
after filtration and purification, (diacetoxyiodo)arenes ArI(OAc)2
in 58–82% yields.
Key words: chromium(VI) oxide, iodoarenes, (diacetoxy-
iodo)arenes, diacetoxylation
(Diacetoxyiodo)arenes, and particularly the parent (diacet-
oxyiodo)benzene, have been known for a long time.1, 2
In this work we applied this method to the oxidation of
They are potent, often selective, oxidizing agents, hence
seventeen iodoarenes (Table 1) with the CrO3/AcOH/
the interest in (diacetoxyiodo)arenes and (diacetoxy-
Ac2O/concd H2SO4 liquid system, followed by mixing the
iodo)benzene is growing rapidly, as demonstrated by a
resulting deep-green reaction mixtures with excess 20%
number of recent reviews.3, 4 They are also used for the
aqueous ammonium acetate solution. Crude crystalline
facile syntheses of, for example, [bis(trifluoroacetoxy)io-
(diacetoxyiodo)arenes, obtained according to Equations 2
do]arenes, [hydroxy(tosyloxy)iodo]arenes (selective oxi-
and 3, were mixed with a little of the hydrolyzed yellow-
dants), and aromatic iodonium salts (arylating reagents).3
ish side products (Equation 4).
There are several preparative methods for these com-
pounds. So far the substrates have generally been:1–4 (i)
iodosylarenes dissolved in glacial acetic acid; (ii)
(dichloroiodo)arenes in which chloride is exchanged by
acetoxy groups coming either from silver, lead(II) or so-
dium acetate, or from acetic acid in the presence of mer-
cury(II) oxide in chlorinated solvents.5 (iii) iodoarenes are
oxidized in warm glacial acetic acid by either peracetic
acid, or sodium perborate,6 or electrolytically. The stan-
dard, and most general, method for the synthesis of (di-
acetoxyiodo)arenes (the oxidative diacetoxylation of ArI
by warm peracetic acid) is, in fact, a very prolonged reac-
tion (12–16 h), and the utmost care should be taken to main-
tain the exact temperature.3 (Diacetoxyiodo)arenes are gen-
erally crystalline compounds, fairly stable in the air, which
may be stored for long periods by avoiding light.
We have previously reported7–11 many short-cut synthe-
ses of diaryliodonium salts. We have oxidized various io-
doarenes ArI (excluding those substituted solely with
stronger electron-donating groups, e.g. OMe), with the
anhydrous CrO3/AcOH/Ac2O/concd H2SO4 liquid mix-
ture, immediately followed by the acidic coupling of the
in situ formed iodine(III) intermediates, ArISO4 and/or
ArI(OSO3H)2, with many activated arenes, Ar’H. The sol-
uble diaryliodonium hydrosulfates thus obtained,
Ar(Ar’)I+HSO–4, were precipitated in the form of insoluble
diaryliodonium bromides, iodides, or perchlorates. We
also established12 that by pouring the deep-green solu-
tions containing chromium(III) salts and ArISO4 and/or
Subsequently, the crude (diacetoxyiodo)arenes, washed
on the filter with cold 10% aqueous acetic acid,13 were
dried and recrystallized from either ethyl acetate or acetic
acid mixed with acetic anhydride (9:1) to acetylate the
yellowish product mixture (Equation 4) to (diacetoxy-
iodo)arenes. Then, to the cooled solutions either hexane or
diethyl ether were added in excess (Table 1) to improve
the crystallization yields. After washing the (diacetoxy-
iodo)arenes on the filter with hexane or diethyl ether, fol-
lowed by air drying, the final yields of pure (diacetoxy-
iodo)arenes were 58–82% (Table 1). Their purity and ho-

SYNTHESIS
Short Papers
Table 1. Preparative Details and Melting Points (Uncorrected) of the (Diacetoxyiodo)arenes Obtained
1722
Entry
Substrate
Producta
Yieldb
(%)
Crystallization
Solventc
mp (dec) (°C);
(Lit.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
C6H5-I
4-FC6H4-I
2-ClC6H4-I
3-ClC6H4-I
4-ClC6H4-I
4-BrC6H4-I
C6H5-I(OAc)2
4-FC6H4-I(OAc)2
2-ClC6H4-I(OAc)2
3-ClC6H4-I(OAc)2
4-ClC6H4-I(OAc)2
4-BrC6H4-I(OAc)2
2,4-Cl2C6H3-I(OAc)2
2,4,6-Cl3C6H2-I(OAc)2
3-NO2C6H4-I(OAc)2
4-NO2C6H4-I(OAc)2
2-MeO; 5-NO2C6H3-I(OAc)2
4-MeO; 3-NO2C6H3-I(OAc)2
2-Me; 5-NO2C6H3-I(OAc)2
4-MeO2CC6H4-I(OAc)2
79d
79
82
82
76
77
75
68
79
60
82
65
58
78
80
79
74
OAcEt/hexane (1:1)
OAcEt/hexane (1:2)
OAcEt/hexane (1:2)
OAcEt/hexane (1:1)
OAcEt/hexane (1:2)
OAcEt/hexane (1:2)
AcOH/Et2O (1:3)
AcOH/Et2O (1:3)
OAcEt/hexane (1:1)
AcOH/Et2O (1:3)
AcOH/Et2O (1:2)
AcOH/Et2O (1:2)
AcOH/Et2O (1:2)
OAcEt/hexane (1:2)
AcOH/Et2O (1:2)
AcOH/Et2O (1:2)
AcOH/Et2O (1:2)
159–161 (161.1–162.2)14
177–178 (177.0–179.8)14
140–142 (140)2
154–156 (153.1–154.7)14
112–115 (109.8–113.2)14
120–122
2,4-Cl2C6H3-I
2,4,6-Cl3C6H2-I
3-NO2C6H4-I
4-NO2C6H4-I
2-MeO; 5-NO2C6H3-I
4-MeO; 3-NO2C6H3-I
2-Me; 5-NO2C6H3-I
4-MeO2CC6H4-I
3-CNC6H4-If
160–162
166–167 (166.8)2
148–150 (151.0–154.2)14
117–121 (167–168)15,e
182–183
153–156
175–177
149–151 (150.0–153.3)14
188–189
f
3-CNC6H4-I(OAc)2f
4-CNC6H4-If
4-CNC6H4-I(OAc)2
172–173
207–208
5-CN; 2-MeOC6H3-If
5-CN; 2-MeOC6H3-I(OAc)2
f
a
Satisfactory microanalyses obtained for the purified products: C ± 0.2, H ± 0.2, I ± 0.2, N ± 0.2%; other halogens were found qualitatively.
For the purified products.
EtOAc and glacial AcOH were admixtured with Ac2O (9:1).
When we enlarged tenfold the preparative scale, the final yield for pure (diacetoxyiodo)benzene was the same.
For C10H10INO6: calcd C, 32.72; H, 2.75; I, 34.57; N, 3.82. Found C, 32.6; H, 2.9; I, 34.5; N 3.7.
CN = cyano group.
b
c
d
e
f
1
are listed in Table 1. As in the previous case,7–11 iodoani-
soles and iodoacetanilides were unsuitable for this meth-
od, since they were quickly oxidized in the solution by
CrO3, with the evolution of iodine vapors, and the forma-
tion of tarry products. 4-Iodotoluene gave 4-(diacetoxy-
iodo)toluene only in 20% yield; as side products we iden-
tified by TLC 4-iodobenzoic acid (40%), the unreacted
4-iodotoluene as well as 4-tolyl acetate. Iodobenzalde-
hydes were smoothly oxidized to iodobenzoic acids
which, in turn, were converted to crude (diacetoxy-
iodo)arenes, which rapidly decomposed on heating during
recrystallization to form CO2 (barium hydroxide test) and
the substrate. 1-(Diacetoxyiodo)-2-nitrobenzene could
not be obtained in its pure crystalline form, though the
corresponding iodine(III) intermediate, 2-NO2C6H4-
ISO4, was formed from 1-Iodo-2-nitrobenzene in the acid-
ic CrO3 solution, which was evidenced by its coupling in
situ with e.g. anisole to form the respective iodonium salt
(86%).8 Lower crude yields (20–60%) of diaryliodonium
salts were obtained, when the previously oxidized
4-iodotoluene8–11 and 4-iodobenzoic acid11 were coupled
in situ with several activated arenes.
Table 2. Spectroscopic H NMR Data (r.t.) of Purified (Diacetoxy-
iodo)arenes
Entrya 1H NMR (CDCl3/TMS) δ
1
2
3
4
5
6
7
8
9
2.01 (s, 6H, MeCO2), 7.45–8.13 (m, 5H, ArH)
2.01 (s, 6H, MeCO2), 7.12–8.14 (sym. m, 4H, ArH)
2.00 (s, 6H, MeCO2), 7.32–8.27 (m, 4H, ArH)
2.02 (s, 6H, MeCO2), 7.41–8.10 (m, 4H, ArH)
2.01 (s, 6H, MeCO2), 7.43–8.06 (sym. m, 4H, ArH)
2.01 (s, 6H, MeCO2), 7.59–7.99 (sym. m, 4H, ArH)
2.00 (s, 6H, MeCO2), 7.31–8.19 (m, 3H, ArH)
2.01 (s, 6H, MeCO2), 7.60 (s, 2H, ArH)
2.04 (s, 6H, MeCO2), 7.70–8.96 (m, 4H, ArH)
2.04 (s, 6H, MeCO2), 8.32 (s, 4H, ArH)
1.99 (s, 6H, MeCO2), 4.13 (s, 3H, OMe), 7.23–9.04 (m,
3H, ArH)
2.02 (s, 6H, MeCO2), 4.06 (s, 3H, OMe), 7.18–8.56 (m,
3H, ArH)
2.02 (s, 6H, MeCO2), 2.86 (s, 3H, Me), 7.70–9.03
(m, 3H,ArH)
2.02 (s, 6H, MeCO2), 3.97 (s, 3H, CO2Me), 8.10–8.20
(sym. m, 4H, ArH)
2.04 (s, 6H, MeCO2), 7.61–8.39 (m, 4H, ArH)
2.03 (s, 6H, MeCO2), 7.76–8.26 (sym. m, 4H, ArH)
1.98 (s, 6H, MeCO2), 7.21–8.42 (m, 3H, ArH)
10
11
12
13
14
15
16
17
a Entries 1–17 correspond to those in Table 1.
In conclusion, we reported a new, quick and inexpensive
method for the effective conversion of various iodoarenes
to the corresponding (diacetoxyiodo)arenes, including (di-
acetoxyiodo)benzene obtained from iodobenzene in 79%
yield. When (diacetoxyiodo)arenes are prepared from ap-
propriate iodoarenes (Table 1), our novel method is 8–16
times faster (30 min as compared with 4–8 h) and ca. 5
times less expensive (taking into account total amounts, and
the respective costs, of all the reagents and solvents ap-
plied) than the method of McKillop and Kemp.6
mogeneity were checked by TLC, their structures were
supported by their melting points, if previously published,
correct elemental analyses (C, H, I, N), and integrated 1H
NMR spectra (Table 2).
The present method is suitable for the seventeen iodoare-
nes, for which the corresponding (diacetoxyiodo)arenes

SYNTHESIS
Deember 1998
1723
The starting iodoarenes ArI were either obtained commercially or by
the reported methods. They were freshly purified prior to use, and
analyzed (C, H, I). H NMR spectra of pure (diacetoxyiodo)arenes
(1) Wilgerodt, C. Ber. Dtsch. Chem. Ges. 1892, 25, 3498.
Willgerodt, C. Die organischen Verbindungen mit mehrwerti-
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1
(Table 2) were taken with a VARIAN (200 MHz) spectrometer in
CDCl3 solutions, at r.t. Microanalyses were carried out at the Institute
of Organic Chemistry, the Polish Academy of Sciences, Warsaw.
The toxic residues left after the acetoxylation reactions were disposed
of according to the local safety measures. We did not recover chromi-
um(III) salts from the residues. This should be taken into account,
when the preparations in larger quantities are intended.
Varvoglis, A. Chem. Soc. Rev. 1981, 10, 377.
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261.
(Diacetoxyiodo)arenes; General Procedure:
Powdered CrO3 (0.67 g, 6.7 mmol; 0% excess) was slowly added por-
tionwise to a stirred mixture of glacial AcOH (5 mL) with Ac2O (3
mL), keeping the temperature below 40°C. The deep-orange solution
was cooled to 10°C, and the appropriate iodoarene (10.2 mmol; 2%
excess to consume all the CrO3, otherwise the final (diacetoxy-
iodo)arenes were contaminated with inseparable Ar-ICrO41, 2) was
added with stirring. Concentrated (98%) H2SO4 (1.32 mL, 24 mmol;
20% excess) was slowly added dropwise, keeping the temperature be-
low 30°C. Next, the mixture was stirred at 40°C for a further 30 min,
then cooled to 5°C. Cold (0–5°C) 20% aq AcONH4 (20 mL; 150%
excess) was rapidly added to the stirred deep-green mixture, which
precipitated out the crude product (sometimes it was oily, but quickly
solidified). The flask was left in a refrigerator for a few hours. The
crystals were collected by filtration, washed with cold (5°C) 10% aq
AcOH (2 × 10 mL),13 until the washings became colorless [all chro-
mium(III) salts, AcONH4, and (NH4)2SO4 were washed off into the
filtrate], and air dried. The yellowish crude products were recrystal-
lized from either AcOH/Ac2O or EtOAc/Ac2O (9:1). After short boil-
ing, the yellowish solutions faded and, after cooling, either hexane or
Et2O were added in excess (Table 1) with stirring. After 30 min, the
crystals were collected by filtration, washed with hexane or Et2O and
air dried. See Table 1 for more details.
Prakash, O. Aldrichim. Acta 1995, 28, 63.
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(9) Farhan, A. N.; Skulski, L. Pol. J. Chem. 1995, 69, 1663.
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(13) The crude (diacetoxyiodo)arenes are more soluble in water than
in 10% aq AcOH, hence washing the crystals with distilled wa-
ter gave lower yields.
†
These results were presented at a Meeting of the Polish Chemi-
cal Society, Poznan´, September 23–26, 1996. They are a part of
the future dissertation of P. Kaz´mierczak, M. Sc.
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