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Lecture 3. Permanganate Oxidation and Nitrobenzene Oxidation

Lecture 3. Permanganate Oxidation and Nitrobenzene Oxidation. Nitrobenzene Oxidation.

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Lecture 3. Permanganate Oxidation and Nitrobenzene Oxidation

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  1. Lecture 3.Permanganate Oxidation and Nitrobenzene Oxidation

  2. Nitrobenzene Oxidation Nitrobenzene oxidation of lignin has long been used in the study of lignin composition. This procedure results in the production of phenolic compounds characteristic of the lignin studied. The procedures used in oxidizing samples vary greatly, with variations occurring in the time, temperature, and method of sample heating; in the amounts of reagents and sample used; and in the extraction procedures

  3. Experimental Procedure The oxidation mixture is heated in a screw-capped test tube equipped with a teflon-lined cap that contains an extra septum (to prevent leakage) made of silicone rubber (.8 mm) wrapped in teflon tape. The tube, containing 1 g of feed (ground to pass through a 1 mm screen), 10 ml of 2 N sodium hydroxide, and 1 ml of nitrobenzene is rotated (5 rpm) in an oven at 160°C for 2 hours.

  4. Experimental Procedure After cooling, the mixture is washed out of the tube (which should not be reused due to weakening of the glass) with distilled water (10 ml) and filtered through a size 15-C fritted glass Buchner funnel. The total filtrate (20 ml) is placed on a 20-ml capacity ClinElut 2 column and extracted with 250 ml of methylene chloride to remove leftover nitrobenzene and nitrobenzene reduction by-products formed during the oxidation process.

  5. Experimental Procedure The sample was is washed off the 20 ml column with 60 ml of distilled water, acidified with 3 ml of concentrated hydrochloric acid, and placed on a 50-ml capacity Chem Tube 2 column and extracted using 250 ml of methylene chloride. The resulting methylene chloride filtrate is then evaporated under vacuum and the sample dissolved in 3 ml of acetone, split into two parts, and dried in .8-ml vials under nitrogen gas (N2), followed by dissolution in TRI-SIL.

  6. Experimental Procedure Analysis by gas chromatography is performed. All chromatography is carried out using silanized glass columns and glass injection port inserts to avoid sample decomposition. Quantitation was performed on a peak area basis. All data were calculated on the basis of percentage of total peak area. Oxidations were carried out in triplicate for all samples.

  7. Experimental Procedure Gas-chromatograph-mass spectrometry is used to identify the products produced by the nitrobenzene oxidation procedure.

  8. Permanganate Oxidation Permanganate Oxidation is similar to nitrobenzene oxidation in that it permits the analysis of both condensed and uncondensed lignin units. In permanganate oxidation, methylated lignin is degraded to aromatic acids by oxidation with KMnO4/NaIO4 with H2O2 treatment. The aromatic acids obtained are esterified with diazomethane and analysed by gas chromatography.

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