To a flask containing 118.0 gm (1.0 mole) of diethyl acetal and 55 gm (0.55 mole) of calcium carbonate is dropwise added 55 ml (1.0 mole) of bromine over a 30-45 min period while keeping the reaction temperature at 5°-10°C. The reaction mixture is allowed to stand 24 hr, steam is introduced to dissolve the salts, the oil separated, dried over potassium carbonate, and distilled to afford 61-83 gm (31-42%), b.p. 167°-170°C. The product is further purified by shaking with potassium carbonate and distilling it under reduced pressure, b.p. 48°-49°C (3 mm Hg). The pure acetal is unstable and becomes colored in a few hours and black after several days. However, the crude acetal boiling at 167°-170°C is stable for several months.
