Diglycolic acid is an aliphatic dicarboxylic acid, its acidity is between the one of acetic acid and oxalic acid. It is formed in the oxidation of diethylene glycol in the body and can lead to severe complications with fatal outcome.

Oxidation of diethylene glycol with concentrated nitric acid was described by A. Wurtz in 1861

In parallel, W. Heintz reported the synthesis of diglycolic acid from chloroacetic acid by heating with sodium hydroxide solution.

In a version with barium hydroxide solution as an alkaline medium, diglycolic acid is obtained in 68% yield after acidification.

The yields of the described reactions are unsatisfactory for use on a technical scale.

The single-stage nitric acid process gives even in the presence of an oxidation catalyst (vanadium(V)oxide) yields of only 58-60%. In a multi-stage process of nitric acid oxidation at 70 °C and multiple crystallization steps, evaporation of the residues and return of the diethylene glycol-containing mother liquor, product yields of up to 99% (based on diethylene glycol) can be achieved.

The oxidation of diethylene glycol with air, oxygen or ozone avoids the use of expensive nitric acid and prevents the inevitable formation of nitrous gases. In the presence of a platinum catalyst, yields of 90% can be obtained by air oxidation.

On a bismuth platinum contact catalyst, yields of 95% are to be achieved under optimized reaction conditions.