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. 2005 Jan 31;10(1):190–194. doi: 10.3390/10010190

Easy and Safe Preparations of (Diacetoxyiodo)arenes from Iodoarenes, with Urea-Hydrogen Peroxide Adduct (UHP) as the Oxidant and the Fully Interpreted 1H- and 13C-NMR Spectra of the Products †

Agnieszka Zielinska 1, Lech Skulski 1,*
PMCID: PMC6147544  PMID: 18007286

Abstract

An easy and safe, though only moderately effective method is presented for preparing (diacetoxyiodo)arenes, ArI(OAc)2, from iodoarenes, ArI, using the commercially available and easily handled urea-hydrogen peroxide adduct (UHP) as the oxidant. The reactions take place in anhydrous AcOH/Ac2O/AcONa (a catalyst) mixtures, at 40 ºC for 3.5 h to afford the purified ArI(OAc)2 in 37-78% yields. The fully interpreted 1H- and 13C-NMR spectra of the ArI(OAc)2 products are reported.

Keywords: (Diacetoxyiodo)arenes, iodoarenes, urea-hydrogen peroxide adduct as oxidant, 1H- and 13C-NMR spectra

Introduction

(Diacetoxyiodo)arenes, ArI(OAc)2, and particularly the parent compound (diacetoxyiodo)benzene, PhI(OAc)2, have been known for a long time [1,2]. They are used in organic synthesis as potent, often chemoselective, oxidizing agents. They are also used for facile syntheses of several classes of aromatic hypervalent iodine compounds, e.g. [bis(trifluoroacetoxy)iodo]arenes, [hydroxy(tosyloxy)iodo]arenes, aromatic iodonium salts [3], etc. In our two latest reviews [4,5] we relate and explain our previous novel syntheses of ArI(OAc)2 from corresponding ArI, as well our novel aromatic iodination methods, and preparations of several classes of aromatic hypervalent iodine compounds, easily attainable from aromatic iodides; particularly see ref. 4, pp. 1343-1345 and 1352-1354.

During the course of our systematic studies on effective and easy preparations of ArI(OAc)2 from the corresponding ArI [4,5], we have devised several methods for their syntheses. In this work we have oxidized seven iodoarenes (Table 1) in anhydrous AcOH/Ac2O mixtures; the reactions did not proceed in the absence of sodium acetate, AcONa (used in a stoichiometric quantity) – cf. our former work [6], where its presence in the reaction mixtures was also indispensable. The reactions took place as follows:

ArI+[urea]···H2O2    →3.5 h ; 40°C AcOH/Ac2O/AcONa     ArI(OAc)2+[acetylurea]+H2O

Table 1.

Final yields and melting points (uncorrected) of the purified (diacetoxyiodo)-arenes obtained from the corresponding iodoarenes.

Substrate Product Yield (%) Mp (°C) Lit. Mp (°C)
C6H5I C6H5I(OAc)2 44 161-162 161-163 [6]
3-FC6H4I 3-FC6H4I(OAc)2 37 143-145 144-145 [8]
4-FC6H4I 4-FC6H4I(OAc)2 78 177-180 179 [8]
2-MeC6H4I 2-MeC6H4I(OAc)2 64 142-147 140-142 [6]
2,4-Me2C6H3I 2,4-Me2C6H3I(OAc)2 69 126-128 128 [9]
2-MeOC6H4I 2-MeOC6H4I(OAc)2 48 145-147 147-149 [6]
3-MeOC6H4I 3-MeOC6H4I(OAc)2 57 130-132 133-135 [6]
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In our opinion, the novel method presented in this paper is easy and safe, albeit only moderately effective (yields are in the 37-78% range). For the first time, we have used UHP as the oxidant. This compound, which is now commercially available, may be considered a “dry carrier” of the unstable and hazardous hydrogen peroxide. The UHP solid is easy to handle, safe and stable at room temperature. Its ability to release oxidative species in water and organic media has made it a useful reagent in organic synthesis [7].

Experimental

General

Melting points submitted in the Table 1 are uncorrected. All the reagents were purchased from Aldrich or Lancaster and were used without further purification. The NMR spectra were run in CDCl3 solutions at room temperature, with TMS as an internal standard; the spectra were recorded on a Brucker AVANCE DMX 400 spectrometer. To obtain better assignments, also 1H – 13C NMR correlation spectra were recorded.

Optimized Procedure for Preparing (Diacetoxyiodo)arenes from Iodoarenes:

Urea-Hydrogen Peroxide adduct, 98% (3.02 g, 31.5 mmol, 350% excess) was added portionwise to a stirred mixture of glacial AcOH (24 mL) with Ac2O (9 mL). An appropriate iodoarene (7 mmol) was slowly added, the solution was cooled to 10-15 °C, and powdered AcONa (1.26 g, 15 mmol) was suspended. Stirring at 40 °C was continued for 3.5 h. After cooling, water (35 mL) was slowly added with stirring. The precipitated ArI(OAc)2 were collected by filtration, washed on the filter with a cold (5-10 °C) 10% aq. AcOH, and air-dried in the dark; if necessary, they were recrystallized from AcOEt/Ac2O (9:1, v/v). The oily or semisolid products were extracted with CH2Cl2, the combined extracts were dried over anhydrous Na2SO4 and filtered, the solvent was distilled off under vacuum, and the solidified residues were recrystallized from AcOEt/Ac2O (9:1).The purities and homogeneities of the purified ArI(OAc)2 were firstly checked by TLC, and next confirmed by their melting points, all close to those reported in the literature (Table 1). Their chemical structures were fully supported by the 1H- NMR (Table 2) and 13C-NMR (Table 3) spectra (in CDCl3).

Table 2.

1H-NMR chemical shifts for pure (diacetoxyiodo)arenes. Cf. our present experimental values with those previously reported [11].

Product Chemical shifts δ (ppm)
H2 H3 H4 H5 H6 OCH3 CH3(o) CH3(p) CH3in OAc
C6H5I(OAc)2 8.10 7.50 7.60 7.50 8.10 - - - 2.01
d t t t d s
3-FC6H4I(OAc)2 7.29 - 7.84 7.51 7.84 - - - 2.02
d t m t s
4-FC6H4I(OAc)2 8.09 7.19 - 7.19 8.09 - - - 2.02
d t t d s
2-MeC6H4I(OAc)2 - 7.52 7.52 7.26 8.17 - 2.72 - 1.98
d t t d s s
2,4-Me2C6H3I(OAc)2 - 7.31 - 7.05 8.04 - 2.68 2.40 1.98
s d d s s s
2-MeOC6H4I(OAc)2 - 7.16 7.59 7.04 8.14 3.99 - - 1.97
d t t d s s
3-MeOC6H4I(OAc)2 7.65 - 7.10 7.41 7.67 3.87 - - 2.02
s d t s s s
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Table 3.

13C NMR chemical shifts for pure (diacetoxyiodo)arenes and coupling constants J 19F−13C and J 19F−C−13C (Hz). Cf. our present experimental values with those previously reported incompletely [10, 12].

Product Chemical shifts of aromatic C atoms in δ (ppm)
C1 C2 C3 C4 C5 C6
C6H5I(OAc)2 121.58 134.94 130.96 131.74 130.96 134.94
s s s s s s
3-FC6H4I(OAc)2 120.65 122.56 161.33 119.26 132.33 130.87
s s d d s s
J = 24.6 J = 253.0 J = 20.7
4-FC6H4I(OAc)2 115.64 137.74 118.59 164.63 118.82 135.95
s s d d d s
J = 22.6 J = 253.7 J = 22.6
2-MeC6H4I(OAc)2 127.29 140.72 128.51 130.97 132.82 137.30
s s s s s s
2,4-Me2C6H3I(OAc)2 124.09 143.73 131.78 140.66 129.40 137.32
s s s s s s
2-MeOC6H4I(OAc)2 113.63 156.46 112.33 134.70 122.91 137.94
s s s s s s
3-MeOC6H4I(OAc)2 121.62 120.68 160.72 118.14 131.73 127.25
s s s s s s
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Product Chemical shifts of C atoms in substituents in δ (ppm)
CH3 (o) CH3 (p) OCH3 CH3 in OAc C=O in OAc
C6H5I(OAc)2 - - - 20.36 176.39
s s
3-FC6H4I(OAc)2 - - - 20.51 176.76
s s
4-FC6H4I(OAc)2 - - - 20.47 176.66
s s
2-MeC6H4I(OAc)2 25.68 - - 20.42 176.53
s s s
2,4-Me2C6H3I(OAc)2 25.56 21.64 - 20.52 176.57
s s s s
2-MeOC6H4I(OAc)2 - - 57.06 20.54 176.82
s s s
3-MeOC6H4I(OAc)2 - - 55.92 20.56 176.64
s s s
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Footnotes

Sample Availability: The samples of pure (diacetoxyiodo)arenes, prepared one year ago and kept in a fridge, have deteriorated in full or in part. Hence, they are not available.

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