In a 2-l. three-necked, round-bottomed flask, fitted with a liquid-sealed mechanical stirrer, a dropping funnel, and an efficient reflux condenser, are placed 720 g. (230 cc., 4.5 moles) of bromine (Note 1) and 1.5 g. of sulfur (Note 2). A glass tube is connected to the top of the condenser to carry the evolved hydrogen bromide to a gas trap. Sixty-nine grams (69 cc., 0.52 mole) of dry paraldehyde (Note 1) is added slowly, with stirring, over a period of about four hours. The reaction proceeds under its own heat during the addition of the paraldehyde; subsequently the mixture is heated externally for two hours at 60–80°. The solution is distilled and a fraction collected over the range 155–175° (Note 3).

On redistillation under reduced pressure there is obtained 220–240 g. (52–57 per cent of the theoretical amount) of reddish yellow bromal, boiling at 59–62°/9 mm., or 71–74°/18 mm.