Methane → [Hydroxy(ethyl)phosphinyl]acetic acid

13.8 g (0.1 mol) of ethyl(2-hydroxyethyl)phosphinic acid (produced as in Example 7) are dissolved in 150 ml of water and adjusted to pH 9 with 2N NaOH solution. Then, 0.45 g of charcoal with 5% Pt and 1% Bi is added, the suspension is heated to 70° C. and air is passed through the suspension at a rate of 10 l/h. All the while, the pH of the suspension is maintained at pH=9 by adding 2N NaOH solution. After the reaction has ended, the reaction solution is filtered to remove the catalyst, which is washed, the filtrate is made acidic with hydrochloric acid and the water is distilled off in vacuo. The residue is taken up in tetrahydrofuran and extracted. The insoluble salts are filtered off to leave 14.0 g (92% of theory) of 2-(ethylhydroxyphosphinyl)acetic acid as colorless solid.