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DOI: 10.1055/sos-SD-120-00173

Yang, Z.; Dong, K.Science of Synthesis Knowledge Updatesearly view.

The oxidation of non-acid-sensitive primary monohydric or dihydric alcohols, including ethylene glycol (ethane-1,2-diol) and hexane-1,6-diol, using nitric acid provides a convenient approach for the synthesis of carboxylic acids. The reactions proceed at a high rate and with the generation of heat and nitrogen oxides, and therefore careful control by alcohol dosage and cooling of the reaction mixture is needed. Nitric acid with a concentration of 75% or higher contains nitronium cations; therefore, the initial product of the reaction of nitric acid with alcohol is thought to be a nitric acid ester, and the formation of the final carboxylic acid depends on the chemical stability of the nitrate. Generally, primary aliphatic alcohols with a simple backbone of any length (pentyl, hexyl, octyl, decyl, and undecyl) are readily oxidized with nitric acid into the corresponding carboxylic acids in 75–90% yield. Ethylene glycol oxidation gives oxalic acid (1) (Scheme 1),[‌3‌] but the reaction exhibited some particular features: For instance, upon mixing the components, the temperature first increased, rising to 60–65°C in a short time period together with vigorous liberation of nitrogen oxides. The reaction mixture then required additional heating for completion of the reaction. This relative stability of ethylene glycol toward the oxidation with nitric acid may be due to the stabilizing effect of the nitrate groups formed by the esterification of glycol.

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