Dioxane tetraketone

September 09, 2019
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Dioxane tetraketone (C4O6) is a chemical curiosity. Also known as dimeric oxalic anhydride, it’s an oxide of carbon; but unlike carbon monoxide and carbon dioxide, it’s difficult to make and impossible to isolate.

Paolo Strazzolini and colleagues at the University of Udine (Italy) and the University of Zagreb (Croatia) synthesized C4O6 in 1998. They combined oxalyl chloride (or bromide) with a suspension of silver oxalate in diethyl ether at –15 to –10 ºC for 1 h, then, also at low temperature, filtered the unreacted silver salt and evaporated the unreacted dihalide and solvent to leave a white solid.

The authors redissolved the product in CDCl3–Et2O and obtained a 13C NMR spectrum that revealed a single peak (other than the ether peaks) at 144.94 ppm. They concluded that the only plausible interpretation of the spectrum was C4O6, which has a calculated peak of 154 ppm.

C4O6 is stable in ether solution at –30 ºC. When the solution is warmed to 0 ºC, the compound decomposes to CO and CO2. Treating C4O6 with methanol gives the mono- and diethyl esters of oxalic acid. With diazomethane, the products are diethyl oxalate and its mono- and bis(diazo) derivatives.

More than two dozen other carbon oxides, ranging from CO3 to C12O12, and with varying degrees of stability, have been reported.

Dioxane tetraketone fast facts

CAS Reg. No. 213967-57-8
Empirical formula C4O6
Molar mass 144.04 g/mol
Appearance White solid
Melting point ≈0 ºC (dec.)
Water solubility Reacts
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