A
500-mL, four-necked, reaction flask, equipped with a
mechanical stirrer,
thermometer, and glass pH electrode combined with an
automatic titrator (Note
1), is charged with
sodium (meta)periodate (85.5 g, 0.4 mol) (Note
2) and water (200 mL). The suspension is cooled to 0°C in an
ice bath and
3 N sodium hydroxide (about 133 mL, 0.4 mol) is added dropwise at a rate such that the temperature does not exceed 7°C. The final pH of the suspension is 5.5. The cooling bath is removed and finely powdered
5,6-O-isopropylidene-L-gulono-1,4-lactone (Note 3) (43.6 g, 0.2 mol) is added in one portion. The temperature of the mixture is kept below 30°C (Note
4). The pH of the suspension is maintained at 5.5 during the course of the reaction by addition of aqueous
15% sodium carbonate (about 15 mL). The suspension is further stirred at room temperature for 30 min, saturated with
sodium chloride (105 g), and filtered by suction using a
Büchner funnel. The white solid (Note
5) is washed thoroughly with two
50-mL portions of brine and the pH of the combined aqueous layers is adjusted to 6.7 with aqueous
15% sodium carbonate before extraction with
dichloromethane (6 × 100 mL) (Note
6). The combined organic extracts are dried over
magnesium sulfate (25 g). The
magnesium sulfate is removed by filtration and washed with two
50-mL portions of dichloromethane. The organic solutions are combined and slowly concentrated to about 50 mL under reduced pressure (Note
7). The remaining solution is placed in a
100-mL, round-bottomed flask equipped with a
Teflon-coated magnetic stirring bar and a
10-cm, vacuum-jacketed, Claisen-Vigreux column (10-mm diameter). With constant stirring by a
magnetic stirrer, the solution is further concentrated by distillation under reduced pressure (400 mbar) at 35°C (bath temperature) (Note
8). The temperature of the
oil bath is then gradually increased to 80°C and the glyceraldehyde acetonide is distilled between 51°C and 52°C. The distillate is collected in a
receiver cooled with an ice-methanol bath (Note
9). Approximately
14.5 g of
L-(S)-glyceraldehyde acetonide (
56% based on
5,6-O-isopropylidene-L-gulono-1,4-lactone) is obtained.