Easy Preparations of (Diacetoxyiodo)arenes from Iodoarenes, with a Urea-Hydrogen Peroxide Adduct (UHP) as the Oxidant
Agnieszka Zielinska and Lech Skulski*
Chair and Laboratory of Organic Chemistry, Faculty of Pharmacy, Medical University,
PL 02-097 Warsaw, Poland, 1 Banacha Street
E-mail: [email protected] ; Tel./Fax: +(4822)5720643
Abstract: Easy, safe and moderately effective novel 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 underwent in anhydrous mixtures, AcOH/Ac2O/AcONa (a catalyst) at 40 ºC for 3.5 h to afford the purified ArI(OAc)2 in 37-78% yields.
Keywords: (diacetoxyiodo)arenes, iodoarenes, urea-hydrogen peroxide adduct as oxidant
(Diacetoxyiodo)arenes, ArI(OAc)2, and particularly the parent (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. See our two latest reviews [4, 5] which relate and explain our former 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.
In the course of our systematic studies on effective and easy preparations of ArI(OAc)2 from corresponding ArI [4, 5], we have devised several methods for their easy syntheses. In this work we have oxidized seven iodoarenes (Table 1) in anhydrous mixtures, AcOH/Ac2O; 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 underwent as follows:
AcOH/Ac2O/AcONa
ArI + [urea] ··· H2O2 ArI(OAc)2 + [acetylurea] + H2O
3. 5 h ; 40 °C
In our opinion, a novel method presented in this paper is easy, safe and moderately effective. It is due to the use of UHP as oxidant, which is now commercially available, and it may be considered as a “dry carrier” of the unstable and hazardous hydrogen peroxide. The solid UHP is easy to handle, safe and stable at room temperature. Its ability to relase oxidative species in organic media has made it a useful reagent in organic synthesis [7].
Experimental
General
Melting points submitted in Table 1 are uncorrected. All the reagents were purchased from Aldrich, and were used without 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.
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 added, the solution was cooled to 10-15˚C, and powdered AcONa (1.26 g, 15 mmol) was suspended. The stirring at 40 ˚C was continued for 3.5 h. After cooling, water (35 mL) was added with stirring. The precipitated ArI(OAc)2 were collected by filtration, washed on the filter with 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 anh. Na2SO4, 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 checked by TLC and their melting points, close to those reported in the literature (Table 1). Moreover, their structures were supported with the 1H NMR (Table 2) and 13C NMR (Table 3) solution spectra (in CDCl3).
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] |
Table 2. 1H NMR chemical shifts for pure (diacetoxyiodo)arenes, in CDCl3 at room temperature.
|
Product |
Chemical shifts d (ppm) |
||||||||
|
H2 |
H3 |
H4 |
H5 |
H6 |
OCH3 |
CH3 (o) |
CH3 (p) |
OAc |
|
|
C6H5I(OAc)2 |
8.10 d |
7.50 t |
7.60 t |
7.50 t |
8.10 d |
- |
- |
- |
2.01 s |
|
3-FC6H4I(OAc)2 |
7.29 d |
- |
7.84 t |
7.51 m |
7.84 t |
- |
- |
- |
2.02 s |
|
4-FC6H4I(OAc)2 |
8.09 d |
7.19 t |
- |
7.19 t |
8.09 d |
- |
- |
- |
2.02 s |
|
2-MeC6H4I(OAc)2 |
- |
7.52 d |
7.52 t |
7.26 t |
8.17 d |
- |
2.72 s |
- |
1.98 s |
|
2,4-Me2C6H3I(OAc)2 |
- |
7.31 s |
- |
7.05 d |
8.04 d |
- |
2.68 s |
2.40 s |
1.98 s |
|
2-MeOC6H4I(OAc)2 |
- |
7.16 d |
7.59 t |
7.04 t |
8.14 d |
3.99 s |
- |
- |
1.97 s |
|
3-MeOC6H4I(OAc)2 |
7.65 s |
- |
7.10 d |
7.41 t |
7.67 s |
3.87 s |
- |
- |
2.02 s |
