Macroporous Polystyrene-Supported (Diacetoxyiodo)benzene: An Efficient Heterogeneous Oxidizing Reagent

Abstract

A heterogeneous, cross-linked macroporous polystyrene-supported (diacetoxyiodo)benzene reagent has been prepared. This reagent is completely insoluble in all solvents and has a rigid pore structure that allows it to function without the need for swelling. Its utility in a variety of oxidation reactions has been demonstrated.

(diacetoxyiodo)benzene - macroporous polystyrene - polymer-supported reagents - oxidation reactions

References and Notes

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See: http://www.polymerlabs.com/stratospheres/index.htm.

<A NAME="RW21206ST-26">26</A> We have previously reported the use of a macroporous polystyrenesulfonic acid reagent: Ueno M. Togo H. Synthesis  2004,  2673 

<A NAME="RW21206ST-27">27</A>

Preparation of 3 A solution of I₂ (22.40 g, 88.20 mmol) in nitrobenzene (250 mL) and CCl₄ (40 mL) was added to macroporous cross-linked polystyrene (20.00 g), followed by a solution of I₂O₅ (8.76 g, 27.56 mmol) in 50% H₂SO₄ (44 mL). The reaction mixture was stirred for 4 d at 85 °C. The reaction mixture was then cooled to r.t., diluted with CHCl₃-MeOH (1:15, 300 mL), and filtered. The collected polymer was washed sequentially with H₂O (3 × 200 mL), AcOH (2 × 200 mL), CHCl₃ (3 × 200 mL) and MeOH (3 × 200 mL) and dried in vacuo to afford iodinated polymer (27.64 g). IR: 2932, 1526, 1340, 1184, 999, 819, 812, 703 cm^-1. Elemental analysis of the product showed the iodine content to be 24.63%, which corresponds to a loading of 1.9 mmol/g.
The iodinated macroporous cross-linked polystyrene (27.0 g)was added to a solution of peracetic acid generated by the dropwise addition of H₂O₂ (30%, 136 mL) dropwise to Ac₂O (500 mL) at 0 °C, which was then allowed to warm to r.t. The suspension was stirred at 40 °C for 16 h and then filtered. The collected polymer was washed with Et₂O (3 × 200 mL) and dried in vacuo to afford 3 (33.0 g). IR: 2930, 1630, 1587, 1483, 1234, 818, 812, 702 cm^-1. Elemental analysis of the product showed the iodine content: 16.68%, which corresponds to a loading of 1.3 mmol/g. The decrease in loading level from 1.9 mmol/g to 1.3 mmol/g indicates essentially quantitative oxidation of the iodine groups on the polymer and both loading levels indicate that approximately 45% of the aryl rings of the polymer were functionalized.

<A NAME="RW21206ST-28">28</A>

This was calculated by determining the ratios of the iodine content of the iodinated polymer (24.63%) to that of 4-ethyliodobenzene (54.69%), and the iodine content of 3 (16.68%) to that of 4-ethyl(diacetoxyiodo)benzene (36.24%). The first ratio (0.45:1) indicates that approximately 45% of the aryl rings of the starting material polymer were iodinated and the second ratio (0.46:1) indicates that essentially all of the iodo groups were oxidized.

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<A NAME="RW21206ST-31">31</A>

Oxidation of Alcohols to the Corresponding Aldehydes and Ketones (Table 1, Entries 1-6) Reagent 3 (0.5 g, 0.65 mmol) was added to a solution of alcohol (0.5 mmol) and TEMPO (9.4 mg, 0.06 mmol) in acetone (3 mL) and the mixture was stirred at r.t. for 2 h. The reaction mixture was then filtered to remove the polymer, which was washed with Et₂O (5 mL). The filtrate was poured into H₂O (10 mL), and extracted with Et₂O (3 × 10 mL). The combined organic layers were dried over Na₂SO₄, filtered, and concentrated in vacuo. The pure product was obtained by filtration of the crude product through silica gel.
Oxidation of Primary Alcohols to the Corresponding Carboxylic Acids (Table 1, Entries 7 and 8) Reagent 3 (1.0 g, 1.3 mmol) was added to a solution of alcohol (0.5 mmol) and TEMPO (39 mg, 0.25 mmol) in acetone (3 mL) and the mixture was stirred at r.t. for 2 h. Then, H₂O (2 mL) was added to the mixture, and the suspension was stirred for an additional 24 h. The reaction mixture was then diluted with Et₂O (5 mL), and HCl (1 N, 3 mL) was added. After stirring for 10 min more, the mixture was filtered to remove the polymer, which was washed with Et₂O (5 mL). The filtrate was extracted with Et₂O (3 × 10 mL). A sat. Na₂CO₃ solution was added to the combined organic layer and then separated. The aqueous layer was neutralized by 1 N HCl and extracted with Et₂O (3 × 10 mL). The combined organic layers were dried over Na₂SO₄, filtered, and concentrated in vacuo to give pure product. Oxidation of Dihydroquinones to the Corresponding Quinones (Table 1, Entries 9 and 10) Reagent 3 (0.5 g, 0.65 mmol) was added to a solution of dihydroquinone (0.5 mmol) in MeOH (3 mL) and the mixture was stirred at r.t. for 4 h. The reaction mixture was then filtered to remove the polymer, which was washed with Et₂O (5 mL). The filtrate was concentrated in vacuo and pure quinone was obtained by filtration of the crude product through silica gel. Oxidation of Diphenyl Sulfide to Diphenyl Sulfoxide (Table 1, Entry 11) Reagent 3 (0.5 g, 0.65 mmol) was added to a solution of PhSPh (0.5 mmol) in CHCl₃-H₂O (99:1, 3 mL) and the mixture was stirred at 40 °C for 72 h. The reaction mixture was then filtered to remove the polymer, which was washed with Et₂O (5 mL). The filtrate was concentrated in vacuo and pure sulfoxide was obtained by filtration of the crude product through silica gel.
Oxidation of AsPh ₃ and PPh ₃ to the Corresponding Oxides (Table 1, Entries 12 and 13) Reagent 3 (0.5 g, 0.65 mmol) was added to a solution of AsPh₃ or PPh₃ (0.5 mmol) in THF (3 mL) and the mixture was stirred at r.t. for 4 h. The reaction mixture was then filtered to remove the polymer, which was washed with Et₂O (5 mL). The filtrate was concentrated in vacuo and the pure oxide was obtained by filtration of the crude product through silica gel.
Oxidation of Diethyl 1,2-Hydrazinedicarboxylate to DEAD (Table 1, Entry 14) Reagent 3 (0.58 g, 0.75 mmol) was added to a solution of diethyl 1,2-hydrazinedicarboxylate (0.5 mmol) in THF (8 mL) and the mixture was stirred at r.t. for 17 h. The mixture was then filtered to remove the polymer, which was washed with Et₂O (5 mL). The filtrate was concentrated in vacuo and pure DEAD was obtained by filtration of the crude product through silica gel.