In a 3-l. round-bottomed flask, fitted with a mechanical stirrer and an inlet tube, is placed 200 g. (253 cc.) of absolute alcohol (Note 1). The flask is surrounded by an ice-salt bath, and the alcohol is saturated with dry hydrogen chloride at 0°. The stem of a 200-cc. separatory funnel is fitted to a one-holed stopper inside a large short-stemmed funnel (Fig. 6). The space between the funnels is filled with finely cracked ice and water. In the separatory funnel is placed 112 g. (2 moles) of cold acrolein (Org. Syn. Coll. Vol. I, 1941, 15) (Note 2).

When the alcohol is saturated with hydrogen chloride, the generator is disconnected and the stem of the separatory funnel is connected to the inlet tube by a rubber tube provided with a screw clamp for adjusting the flow. The acrolein is added, with stirring, to the alcoholic hydrogen chloride solution at about 0°. The addition should require from one to two hours. After two layers have formed, the lower layer of acetal is separated and treated gradually with powdered sodium bicarbonate until all acid is neutralized (Note 3). The mixture is filtered. The filtrate is washed with two 50-cc. portions of ice water and dried over 10 g. of potassium carbonate for five to ten hours (Note 4). It is then filtered and distilled under reduced pressure. The yield of product boiling at 58–62°/8 mm. is 112 g. (34 per cent of the theoretical amount).