[A007]
Easy Preparations of [Bis(trifluoroacetoxy)iodo]arenes from Iodoarenes, with Sodium Percarbonate as the Oxidant
Pawel Kazmierczak 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
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Abstract: Easy and effective preparations of the nearly pure [bis(trifluoroacetoxy)iodo]arenes, ArI(OCOCF)3, from some iodoarenes, ArI, are reported, using an anhydrous sodium percarbonate/(CF3CO)2O/CH2Cl2 system. The colorless ArI(OCOCF3)2 thus obtained were 98-99% pure, which was established iodometrically.
Keywords: [bis(trifluoroacetoxy)iodo]arenes from iodoarenes, sodium percarbonate as oxidant
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[Bis(trifluoroacetoxy)iodo]arenes, ArI(OCOCF3)2, are potent and selective oxidants, widely used in modern organic synthesis. So far, they have been synthesized from either ArI, or ArIO, or ArICl2, but the most common method depends on their preparing (in moderate yields) from the corresponding (diacetoxyiodo)arenes, ArI(OAc)2, by their recrystallization from CF3COOH [1, 2]. Recently, in our laboratory we have worked up a simple, easy, and efficient method for the direct preparing ArI(OCOCF3)2 from the respective iodoarenes, ArI, in a binary anhydrous solvent system, (CF3CO)2O/CH2Cl2, with commercial sodium percarbonate, 2Na2CO3 . 3H2O2, used as the oxidant; exemplarily:
Optimized Procedure for Preparing [Bis(trifluoroacetoxy)iodo]arenes from Iodoarenes:
A solution of an appropriate iodoarene (5 mmol) in a mixture of (CF3CO)2O (12 mL) with CH2Cl2 (40 mL) was cooled with stirring to 0-2 oC. Next, sodium percarbonate (2.1 g; 13.4 mmol; 300% excess) was added portionwise, and the stirring was continued for 2 h at 0-2 oC, and at room temperature for ca. 18 h. The precipitated CF3COONa was collected by filtration under reduced pressure, washed with CH2Cl2 (2 x 20 mL), and discarded. The filtrates were evaporated under vacuum. The solid residues were triturated with hexane (10 mL), collected by filtration, washed with hexane on the filter, and quickly air-dried by the suction, leaving the colorless title products, ArI(OCOCF3)2 (40-87% yields). Their yields and melting points are given in Table 1 below. Practically, these products need not to be recrystallized. They should be stored in the dark, preferably in a cooler, with avoiding the moisture [3]. They were 98-99% pure, established iodometrically.
Table 1. Yields and melting points (uncorrected) for the [bis(trifluoroacetoxy)iodo]arenes obtained.
|
Ar |
Yield [%] |
Mp [oC] |
Lit. Mp [oC] |
|
phenyl |
87 |
122-124 |
120-122 [4] |
|
2-methylphenyl |
81 |
89-92 |
88-90 [4] |
|
3-methylphenyl |
86 |
93-96 |
87-90 [5] |
|
4-methylphenyl |
76 |
112-115 |
114-116 [4] |
|
4-fluorophenyl |
77 |
103-105 |
88-90 [4] |
|
4-chlorophenyl |
74 |
129-132 |
131-133 [5] |
|
3-(trifluoromethyl)phenyl |
40 |
97-100 |
99-100 [6] |
References
[1] Varvoglis, A. The Organic Chemistry of Polycoordinated Iodine; VCH: Weinheim, 1992.
[2] Varvoglis, A. Hypervalent Iodine in Organic Synthesis; Academic Press: San Diego, 1997.
[3] Aldrich Handbook of Fine Chemicals and Laboratory Equipment 2000-2001, p. 225; it reports m. p. 121-125 oC for PhI(OCOCF3)2, 97%, with a note: MOISTURE-SENSITIVE.
[4] Kasumov, T. M.; Brel, V. K.; Grishin, Y. K.; Zefirov, N. S.; Stang, P. J. Tetrahedron 1997, 53, 1145.
[5] White, J. D.; Caravatti, G.; Kline, T. B.; Edstrom, E.; Rice, K. C.; Brossi, A. Tetrahedron 1983, 39, 2393.
[6] Yagupol'skii, L. M.; Maletina, I. I.; Kondratenko, N. V.; Orda, V. V. Synthesis 1977, 574.