A 1-l. three-necked flask is fitted with a stirrer, a reflux condenser with a tube leading to a flask of water for absorption of hydrogen bromide, and a separatory funnel with a stem drawn to a fine tip which reaches almost to the blades of the stirrer. In the flask are placed 160 g. (1 mole) of diethyl malonate (Note 1) and 150 cc. of carbon tetrachloride. In the separatory funnel is placed 165 g. (53 cc., 1.03 moles) of dry bromine (Note 2). The stirrer is started, and a few cubic centimeters of bromine are run into the solution. A large electric bulb is held under the flask until the reaction starts. Then the rest of the bromine is added gradually at such a rate as to keep the liquid boiling gently. It is then refluxed until no more hydrogen bromide is evolved (about one hour).

The mixture is cooled and washed five times with 50-cc. portions of 5 per cent sodium carbonate solution. It is then distilled under reduced pressure, fractions being taken up to 130°/40 mm. and at 130–150°/40 mm. The residue amounts to about 20 g. (Note 3). The lower-boiling fraction is redistilled. The combined fractions boiling at 130–150°/40 mm. are redistilled under reduced pressure. The product boiling at 132–136°/33 mm. (121–125°/16 mm.) amounts to 175–180 g. (73–75 per cent of the theoretical amount). Redistillation of the low fractions gives about 15 g. more of the product.