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Oxidative degradation of aromatic ring; pyrazine-2,3,5-tricarboxylic acid

SyntheticPage 270
DOI: 10.1039/SP270
Submitted Jun 01, 2008, published Jun 01, 2008
Jan Martin Becker (J.M.Becker@warwick.ac.uk)
A contribution from Scott group, Warwick University


			Reaction Scheme: Oxidative degradation of aromatic ring

Chemicals Used

(1R,2S,3R)-1-(quinoxalin-2-yl)butane-1,2,3,4-tetraol (Page 269)
Potassium hydroxide (Aldrich)
Potassium permanganate (Aldrich)
Nitric acid (Fisher)
Silver Nitrate (Johnson Matthey)
Hydrochloric acid (Fisher)

Procedure

2-tetrahydroquinoxaline (15.0 g, 60.0 mmol) was placed in a 3-L three-neck round-bottom flask equipped with a mechanical stirrer, thermocouple and a solid addition funnel. The golden solid was suspended in distilled water (1500 ml), heated to 40ºC and the mixture basified with potassium hydroxide (7.50 g. 133 mmol) to yield a deep red solution. The solution was heated to 90ºC and treated with small portions of solid potassium permanganate (20 x 5.5 g, 696 mmol) over 1.5 h. Slow addition was paramount, as the oxidation of the carbon skeleton was accompanied by strong effervescence due to the elimination of CO2 from the solution at the elevated temperature. After stirring the solution for 1 h at 90ºC, any unreacted potassium permanganate was removed by the addition of methanol (10 cm3) and the suspension filtered hot to remove the brown manganese dioxide. The solids were washed with boiling water (5 x 50 cm3) and the combined filtrates were concentrated under reduced pressure ( ca. 30 cm3) to yield a pale yellow solution. The solution was brought to pH = 6 with the addition of conc. HNO3 (s.g. 1.42, 70 %) and boiled for 15 min. to remove excess CO2. The solution was left to cool to ambient temperature and treated with silver(I) nitrate (35 g, 205 mmol) in distilled water (50 cm3) to precipitate the yellow silver complex of the triacid. The complex was isolated by filtration and dried on the filter for 15 min. The material was light sensitive and unduly exposure to light caused decomposition by a colour change to grey, therefore this procedure was conducted in a darkened fumehood. The obtained solid was treated twice with hot aqueous hydrochloric acid (2 x 100 cm3, 2M), filtered to remove the precipitated silver chloride and the solid was washed once more with hot hydrochloric acid (100 cm3, 2M) to remove any residual product. The filtrates were combined, left to cool to ambient temperature and concentrated under reduced pressure to roughly half the starting volume (ca. 150 cm3), upon which the title compound began to separate out as a white crystalline solid. The solid was isolated by filtration and dried in a vacuum desiccator over P2O5 for several hours. (4.90 g, 30 %). Two further crops of material were obtained upon further concentration to ca. 20 cm3 (2.32 g, 18.5 %) and prolonged storage of the filtrate at +4ºC (1.09 g, 9 %). The total yield was recorded as (8.31 g, 66 %).

Author's Comments

The quoted yield is close to reported literature results. Has been performed several times.

Data

1H NMR (400 MHz, DMSO-d6): 9.23 (s) ESI MS (+ve): 213 (M+H+)

Lead Reference

H. I. X. Mager and W. Berends, Recueil des Travaux Chimiques des Pay-Bas et de la Belgique, 1958, 77, 827-841.

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Keywords: aromatics/arenes, carboxylic acids, degradation, oxidation

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