(A) Preparation of Thiocarbonyl Perchloride.—In a 5-l. bottle arranged for cooling by running water is placed 500 g. (398 cc., 6.58 moles) of dry carbon disulfide (Note 1) to which 0.5 g. of iodine has been added. Dry chlorine is passed into the cooled carbon disulfide at such a rate that the temperature does not rise above 25°, until the liquid weighs 1770 g. (17.9 moles of chlorine) (Note 2). The time required is about forty hours. The product, a mixture of impure thiocarbonyl perchloride and sulfur chloride, is a deep red liquid.

The apparatus illustrated in Fig. 27 is assembled, in a large hood if possible (Note 3). A is a 5-l. round-bottomed flask heated by a large ring burner and provided with a specially treated four-holed cork stopper covered with tin foil (Note 4). To these holes are fitted the column D, the tube B reaching to the bottom of A, the specially bent tube C reaching up the inside of D, and the tube K connected with the tubes leading to the 2-l. separatory funnel H, so that the distance between the stopper of A and the stopcock of H is at least 100 cm. The bottom of the column D is of 20-mm. bore; the main portion is of 30 mm. The side arm should be at least 85 cm. above the stopper of A. The tube C should reach about half way up the inside of the column D. The column is filled with pieces of 3-mm. glass tubing about 5 mm. long. Its top is provided with a cork covered with tin foil and fitted fairly loosely so as to blow out in case of a clogging of the apparatus. It should be held by a wire to prevent its being blown out entirely. Tubes B and C are connected with a steam line or steam generator of large capacity. The separatory funnel H is placed at the highest available level (Note 5) and connected with the tubes I, J, and K in such a manner as to secure a pressure of liquid sufficient to more than balance the steam pressure (Note 6). E and F are specially constructed condensers of unusual length (160 cm. and 85 cm., respectively) and bore (40 mm.) made from large glass tubing and rubber stoppers (Note 7). The top of condenser F is connected to a good draft chamber or to a gas-absorption trap (Fig. 7 on p. 97). G is a 5-l., or better, a 12-l. round-bottomed flask which is used as a receiver.

The crude chlorinated mixture is steam-distilled in this special apparatus to obtain thiocarbonyl perchloride and to decompose the sulfur chloride. In flask A is placed 1210 cc. of water which is heated to boiling by means of the ring burner. Steam is passed in through tubes B and C. The chlorinated mixture is placed in the separatory funnel H, and the connecting tubes are filled with the liquid which is allowed to pass into A at about 5 drops per second (Note 8). Sulfur begins to separate in the column and in the condensers. The steam distillation requires about five hours and gives 10–12 l. of distillate consisting of water, sulfur, and a heavy red oil. The water is decanted and the rest of the mixture is filtered by suction through glass wool. The oil is separated and dried over about 10 g. of calcium chloride.

The crude, dry thiocarbonyl perchloride is distilled through an efficient 60-cm. column (Note 9). The distillate below 140° is discarded. The fraction boiling at 140–155° at atmospheric pressure amounts to about 600 g. The boiling point of pure thiocarbonyl perchloride is 149°.

(B) Reduction of Thiocarbonyl Perchloride to Thiophosgene.—The apparatus illustrated in Fig. 28 is assembled. A is a 5-l. round-bottomed flask heated by a ring burner and provided with a two-holed, specially treated cork (Note 4) carrying tube B of about 40-cm. length connected with condenser C of about 115-cm. length, and tube R which conveys the perchloride from the separatory funnel T (Note 6). R is 6-mm. tubing of about 90-cm. length and must reach to the bottom of A. D and G are specially blown connecting tubes, D reaching through the cork of F and G reaching to the bottom of the 5-l. flask, F. Each arm of D is about 20 cm. long and of 2-cm. bore. The vertical arm of G is of about 3-cm. bore and its side arm of about 1-cm. bore. H and I are efficient bulb condensers at least 60 cm. long. F is provided with siphon E for removing the product. L is a tall tower (about 50 cm. in length) packed with short pieces of glass tubing alternating with layers of glass wool. Its stopper carries the tube K reaching to the bottom of the tower, a separatory funnel, and an exit tube M leading to the draft. P is a siphon for removing the xylene wash liquid.

In the flask A are placed 750 g. (6.3 atoms) of granulated tin (Note 10) and 1500 cc. of commercial hydrochloric acid (about 28 per cent). The mixture is heated until the action is vigorous. The thiocarbonyl perchloride is run in from the funnel T (Note 11). The resulting reaction is very violent. The vapors are condensed in the series of condensers and in the scrubber L through which xylene is allowed to flow slowly from the separatory funnel N. Most of the crude thiophosgene collects in F, although a small amount is obtained from the distillation of the xylene wash liquid.

The crude thiophosgene is separated and dried with about 10 g. of calcium chloride, and fractionated with a good column. Very little distils below 73°. The fraction boiling at 73–76° at atmospheric pressure is pure thiophosgene and amounts to about 180 g. (24 per cent of the theoretical amount) (Note 12). The fraction above 76° is largely thiocarbonyl perchloride and may be again reduced or added to the reduction in a subsequent run.