A. 1,1-Cyclobutanedicarboxylic acid. In a 3-l. three-necked round-bottomed flask, carrying a separatory funnel, a mechanical stirrer, a reflux condenser fitted with a calcium chloride tube, and a thermometer, are placed 160 g. (1 mole) of ethyl malonate and 212 g. (1.05 moles) of trimethylene bromide. The thermometer is adjusted so that the bulb is immersed in the liquid in the flask; the stirrer is started, and a solution of 46 g. (2 gram atoms) of sodium in 800 ml. of absolute ethanol is added through the separatory funnel while the temperature of the reaction mixture is kept at 60–65° (Note 1). During the addition of the first quarter of the ethoxide solution (20 minutes) it is necessary to cool the reaction mixture occasionally in order to maintain the proper temperature, but after this point the remainder of the ethoxide solution is added just rapidly enough to keep the reaction mixture at 60–65°; this part of the addition requires about 30 minutes.

The reaction mixture is allowed to stand until the temperature drops to 50–55°, after which it is heated on a steam bath until a sample added to water is neutral to phenolphthalein (about 2 hours). Water is added to dissolve the precipitate of sodium bromide, and the ethanol is removed by distillation. The flask is now arranged for steam distillation, and the ethyl 1,1-cyclobutanedicarboxylate and unchanged malonic ester are removed by steam distillation (Note 2); about 4 l. of distillate is collected. The ester layer in the distillate is separated, and the aqueous layer is extracted once with 1 l. of ether. The extract and the ester layer are combined, and the ether is removed on the steam bath (Note 3).

The esters are hydrolyzed by refluxing them for 2 hours with a solution of 112 g. of potassium hydroxide in 200 ml. of ethanol. Most of the ethanol is removed by distillation, and the mixture is then evaporated to dryness on a steam bath. The residue is dissolved in the minimum amount of hot water (100 to 125 ml.), and concentrated hydrochloric acid (about 90–95 ml.) is added until the solution is slightly acid (Note 4). After the solution has been boiled for a few minutes to removed carbon dioxide, it is made slightly alkaline with ammonia. To the boiling solution there is added a slight excess of barium chloride. The hot solution is filtered to remove barium malonate, the filtrate is cooled, and to it is added 100 ml. of 12 N hydrochloric acid. The solution is then extracted with four 250-ml. portions of ether. The extracts are combined and dried over calcium chloride, and the ether is removed by distillation on a steam bath. The residual pasty mass (about 38 g.) is pressed on a porous plate to remove adherent oil and then dissolved in 30–50 ml. of hot ethyl acetate. The solution, when cooled in an ice-salt bath, deposits the pure dicarboxylic acid. This is filtered; the filtrate, when evaporated, yields a pasty mass of acid which, in turn, is crystallized from ethyl acetate. The yield of pure 1,1-cyclobutanedicarboxylic acid melting at 156–158° is 30–34 g. (21–23%).

B. Cyclobutanecarboxylic acid. The above dibasic acid is placed in a 75-ml. distilling flask carrying a thermometer and attached to a 75-ml. Claisen flask as a receiver. The receiver is cooled with running water while the flask containing the dibasic acid is heated in a metal or oil bath (bath temperature, 160–170°) until no more carbon dioxide is evolved. Then the temperature of the bath is raised to 210–220°, and the material that boils at 189–195° is collected. The crude cyclobutanecarboxylic acid (19–22 g.) is redistilled from the Claisen flask in which it was collected. The pure acid boils at 191.5–193.5°/740 mm. (Note 5) and weighs 18–21 g. (18–21% based on malonic ester). There is a small higher-boiling fraction, which comes over at 193.5–196°/740 mm.