Hydrochloric Acid → Tetrahydrofolic acid

Participants

Reaction Steps

To a suspension of folic acid dihydrate (47.8 g, 100 mmol) in deaerated H2O (1,000 ml), which was cooled in an ice bath, was added slowly with stirring 50% NaOH (10.5 ml). The resulting dark yellow solution (pH 8.0, meter) was treated over a 10-min period with a solution of NaBH4 (58 g) in H2O (150 ml). The solution was stirred for an additional 30 min, the pH increasing during this period from 8.4 to 8.8. Excess NaBH4 was decomposed by the addition of 6 N HCl (caution, vigorous effervescence) until the pH of the solution was 6.8. Solid ascorbic acid (5 g) was added and stirring continued until complete dissolution occurred. The resulting solution was adjusted to pH 3.7 with 6 N HCl (total volume, 165 ml). The cream-colored precipitate was collected by filtration under N2, washed with ice cold HCl (pH 3.5, 200 ml) containing ascorbic acid (2 g) and dried to constant weight in vacuo over P2O5 at room temperature: yield, 60.0 g (96%). Solutions for the uv spectra determinations were obtained by dissolution of tetrahydrofolic acid (5.5 mg) by the successive addition of mercaptoethanol (2.5 ml) and water (22.5 ml) and dilution of the resulting stock solution with the appropriate solvent (5→50 ml). λmax, nm (ε×10-3): 0.1 N HCl-270 (23.5), 292 (20.8); pH 7-297 (25.7); 0.1 N NaOH-297 (25.9). TLC [DEAE cellulose; 0.005 M KH2PO4 +0.5 M NaCl+0.2 M mercaptoethanol (pH 7)]-Rf ~0.44 (elongated).

Provenance & Evidence