GC_MS
(Hive Bee)
09-01-02 23:53
No 351495
      Enhance oxidative strenght of 30% H2O2
(Rated as: excellent)
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A Method For Increasing The Oxidizing Effectiveness Of 30% Hydrogen Peroxide

Jonathan BLUM, Yechiel PICKHOLTZ, Harold HART(*)

(*) Dpt Of Organic Chemistry, The Hebrew University, Jerusalem, Israel

Synthesis 04 (1972) 195


Concentrated hydrogen peroxide (>50%, and particularly 90-98%) is a useful reagent, especially in an acidic medium, for a variety of organic oxidations. Unfortunately, the product is not universally manufactured and is unavailable in some parts of the world because of shipping restrictions. To circumvent this difficulty we here report a method for increasing the oxidizing effectiveness of the generally available 30% hydrogen peroxide.
In the present example, 30% hydrogen peroxide was added, in the cold, to an excess of acetic anhydride and concentrated sulphuric acid. Though the addition was strongly exothermic, it was easily controlled. The resulting solution readily oxidized hexamethylbenzene to hexamethyl-2,4-cyclohexadienone in a yield (86%) comparable with that reported using 90% hydrogen peroxide in an acetic acid/sulfuric acid mixture of peroxytrifluoroacetic acid/boron fluoride.

[ reaction scheme hexamethylbenzene -> hexamethyl-2,4-cyclohexadienone ]


Hexamethyl-2,4-cyclohexadienone

In a three-necked flask provided with a mechanical stirrer, dropping funnel and thermometer, a mixture of acetic anhydride (36 mL) and concentrated sulfuric acid (9 mL) was cooled to -5C. To this mixture, 30% hydrogen peroxide was added dropwise with vigorous stirring over a period of 25 minutes, so as to maintain the internal temperature to -3C to -5C. After the addition was completed, the white slurry was diluted with DCM (25 mL) and the resultant solution was added rapidly (3 min) at 0C to a mixture of hexamethylbenzene (8.0 g), DCM (30 mL), acetic acid (36 mL), and concentrated sulfuric acid (27 mL). The ice/salt bath was replaced by ice water and stirring was continued for 90 min, during which time the hydrocarbon dissolved. The yellow solution was poured into ice water (150 mL). The aqueous layer was extracted with DCM (3x50 mL). The combined organic layers were washed with 100 mL-portions of water, 5% NaOH, saturated iron(II) ammonium sulfate, and again (2x) with water. The dried solution (magnesium sulfate) was concentrated in vacuo and the residue distilled in vacuo: yield: 7.5 g (86%) of yellow, oily product; bp: 76-80C/0.25 mm. The IR and NMR spectra were identical to those reported; the product was 97% pure, and contained 3% of unoxidized hexamethylbenzene.

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Note: SWiM reads this as follows: make the 'super hydrogen peroxide' with the acetic anhydride and add it to a mixture of your most beloved phenyl propenyl derivate, which is diluted in a mixture of acetic acid, DCM and concentrated sulfuric acid. The concentrated sulfuric acid worries SWiM, as it might turn your o so precious olefine into a black mess... yes, ladies and gentlemen... tar. SWiM couldn't test the procedure yet, since he won't be in a lab for the coming 2-3 weeks.

Doped(TM) since 19.... euhm... a long time smile