Under stirring conditions, dimethyl phosphite (10.0 mL, 109 mmol), triethylamine (1.5 mL, 10.9 mmol) and paraformaldehyde (3.26 g) were mixed. The mixture was heated in an oil bath (external temperature) at 100°C. After 2.5 hours of reaction, the mixture was cooled to room temperature and subsequently concentrated under vacuum. The residue was purified by fast column chromatography (eluent: ethyl acetate/methanol, 95:5, v/v) to afford dimethyl hydroxymethylphosphonate as a colorless oil (9.41 g, 62% yield). The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 4.32 (1H, br s), 3.95 (2H, d, J = 6 Hz), 3.83 (3H, s), 3.81 (3H, s); 31P{1H} NMR (400.1 MHz, CDCl3): δ 27.8; 13C NMR (100.6 MHz. CDCl3): δ 53.5, 56.0, 57.6.
