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L-ascorbic acid (52.8 g, 0.3 mol) was dissolved in deionized water (410 mL). Calcium carbonate (60.06 g, 0.6 mol) was added to this solution and the reaction mixture was cooled to 0-5 °C. Under stirring, 50% (w/w) hydrogen peroxide solution (61.2 mL, 0.9 mol) was slowly added dropwise, controlling the reaction temperature at 5-20 °C. After the dropwise addition, the reaction mixture was continued to be stirred at room temperature for 16 hours. Subsequently, the reaction mixture was heated to 70-75 °C and maintained for 1 h until no oxygen was released. The reaction mixture was filtered while hot and the filter cake was washed with hot water at 50-60 °C (30 mL × 2). The filtrates were combined and concentrated under reduced pressure to about 20 mL at 55 °C. Methanol (250 mL) was added slowly and dropwise to the warmed concentrate (about 50 °C) until the solution became turbid, and then stirred for 12 h at room temperature. The precipitate was filtered and washed with methanol (30 mL × 3). The resulting solid was dried to constant weight at 60 °C (about 3 h) to give calcium L-threonate 45.2 g in 94.6% yield. The product was characterized by IR (KBr) and 1H-NMR (D2O, 400 MHz), and the data were consistent with those reported in the literature.