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    8. Pt-catalyzed Oxidation of THF. Pt black (19.5 mg, 0.1 mmol) was stirred in 1.0 mL of D₂O in a 5-mL pear-shaped flask with a rubber septum. THF (40.5 uL, 0.5 mmol) was added through a microsyringe. After the solution was heated in an oil bath at 95°C for a 24-36 h under 1 atm of O₂, the flask was cooled in an ice-water bath and then left at room temperature for 30 min, while Pt black settled out. Finally, 0.6 mL of solution was taken for the ¹H-NMR spectrum which indicated the sole organic products were gamma-butyrolactone abd DOCH₂CH₂CH₂COOD (96.0% combined yield relative to THF).

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Here the same reaction is done with platinum metal, both with and without acetone co-solvent. Chem.Ber. 109, 3707-3727 (1976). Don't ask me for a complete translation, I can barely read it.

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    Oxidation von Tetrahydrofuran (19): a) 3.6 g 19 in 50 ml 80 proz. Aceton wurden mit 1g Platin 10 h bei 25°C unter O₂ gerührt. Der Umsatz an 19 wurde gaschromatographisch (Säulde D) zu 72% bestimmt. Die eingeengte Lösung wurde mit Benzol extrahiert. Aus der benzolischen Lösung wurden 2.1 g gamma-Butyrolacton (21) erhalten. Sdp. 90-92°C/8 Torr. 21 stimmte gaschromatographisch und spektrokopisch mit authent. Material überein. Aus dem wäßr. Rückstand der Benzolextraktion wurden 0.18 g kristallines Material gewonnen, das IR-spektrokopisch als Bernsteinsäure (german for succinic acid) (24) indentifiert wurde. Schmp. 186-187°C. Keine schmp.-Depression mit authent. Probe.
     b)25 g 19 wurde ohne Lösungmittel (without solvent medium, only THF that is) in Gegenwart von 5 g Platin 10 h bei 25°C oxidiert. Das Verhältnis von Lacton 21 zu Säure 24 wurde gaschromatograpisch bestimmt zu 88:12 (Säule B). Nach der Aufarbeitung wie unter a) wurden 10.5 g 21 und 1.7 g 24 erhalten.

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And here is an oxidation catalyzed by anhydrous cobalt(II)chloride in 1,2-dimethoxyethane from J.Mol.Catal. 72, 143-152 (1992). Anhydrous conditions is a must or otherwise the cobalt chloride will be complexed to water instead of anything else. The isolated yield for GBL was only 34%, the other product (43%) being 2-(HCOOCH₂CH₂CH₂O)-tetrahydrofuran.

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General procedure for the oxidation of ethers.
    A mixture of the ether (5.0 mmol) and ahydrous CoCl₂ (3.3 mg, 0.025 mmol) in DME (10-15 ml) was stirred under an oxygen atmosphere (1 atm) for 3-72 h at 40-90°C. The reaction was monitored by gas chromatography. A pink precipitate appeared towards the end of the reaction. Following completion, the mixture was cooled to room temperature and filtered through a small silica column to remove the pink precipitate. The filtrate was concentrated by rotary evaporation, distilled water (10 ml) was added to the resulting oil and the products were extracted with ether (3x20 ml). The organic layer was washed with distilled water (50 ml), dried (MgSO₄), and concentrated. Pure compounds were isolated by thin layer or column chromatography of the crude material on silica gel using various ratios of ether/hexane as the eluant, and were characterized by IR, proton and carbon NMR and mass spectrometry.

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And where would one get 1,2-dimethoxyethane OTC? I think 2-methoxyethanol (monomethyl ethylene glycol) was available easily. It can be reacted in presence of sulfuric acid according to Patent DE659879. Not worth the trouble if you ask me.

There is a host of other transition metal oxidation catalysts to do the job but many of then require exotic ligands. High pressure is also an option, described in numerous patents, but who would really like that? Some kind of a KRV might help reducing the amount of catalyst to get the reaction through in a sensible time, but that would require cold-headed experimentation.


EDIT: I forgot to include a few details from the CoCl₂ reaction that were in a table. For THF, the reaction temperature was 40°C, reaction time 48 h, conversion 87% and 1,2-dimethoxyethane was NOT USED AT ALL ("In the absence of DME" they say).  The article is very thorough and describes the reaction mechanism and the effect of the solvent on the reaction. I'll have to read and think about the thing a bit more, although it seems the solvent is no longer a problem. It might even be possible to modify the reaction conditions so that the side reaction wouldn't eat such a big portion from GBL yields...

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General procedure for the oxidation of ethers.
A mixture of the ether (5.0 mmol) and ahydrous CoCl2 (3.3 mg, 0.025 mmol) in DME (10-15 ml) was stirred under an oxygen atmosphere (1 atm) for 3-72 h at 40-90°C. The reaction was monitored by gas chromatography. A pink precipitate appeared towards the end of the reaction. Following completion, the mixture was cooled to room temperature and filtered through a small silica column to remove the pink precipitate. The filtrate was concentrated by rotary evaporation, distilled water (10 ml) was added to the resulting oil and the products were extracted with ether (3x20 ml). The organic layer was washed with distilled water (50 ml), dried (MgSO4), and concentrated. Pure compounds were isolated by thin layer or column chromatography of the crude material on silica gel using various ratios of ether/hexane as the eluant, and were characterized by IR, proton and carbon NMR and mass spectrometry.
EDIT: I forgot to include a few details from the CoCl2 reaction that were in a table. For THF, the reaction temperature was 40°C, reaction time 48 h, conversion 87% and 1,2-dimethoxyethane was NOT USED AT ALL ("In the absence of DME" they say). The article is very thorough and describes the reaction mechanism and the effect of the solvent on the reaction. I'll have to read and think about the thing a bit more, although it seems the solvent is no longer a problem ". It might even be possible to modify the reaction conditions so that the side reaction wouldn't eat such a big portion from GBL yields...

I´d bet acetone would work very well as solvent in the Co(II)Cl oxidation.

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Nice. Is Co(II)Cl expensive??. If not Can't this bee a superior reaction to make GBL??