A solution of 315 g. (4.76 moles) of potassium hydroxide in 3150 ml. of commercial absolute ethanol is prepared with mechanical stirring in a 5-l. three-necked round-bottomed flask. The flask is fitted with a 500-ml. dropping funnel and a gas inlet tube extending to the bottom of the flask, and hydrogen sulfide is passed in through the inlet tube with stirring until the solution is saturated and no longer gives an alkaline reaction with phenolphthalein (Note 1), (Note 2). The mixture is cooled to 10–15° by means of an ice bath, and 346.5 g. (2.46 moles) of redistilled benzoyl chloride is introduced dropwise with stirring while the temperature is kept below 15°. The potassium chloride which precipitates during the addition (Note 3) is separated by filtration with suction through a Büchner funnel and is washed with about 200 ml. of ethanol (Note 4). The filtrate and washings are cooled to 10–15°, and solid iodine is added slowly, with constant agitation, until a slight excess is present, as shown by a faint permanent coloration of the solution. The amount of iodine required varies from 336 g. to 407 g. (1.32–1.61 moles) (Note 5). Benzoyl disulfide precipitates during the addition. It is collected on a filter and washed with 750 ml. of 95% ethanol followed by 3 l. of water. The crude product, after drying at room temperature, or in an oven at a temperature which does not exceed 60° (Note 6), weighs 325–333 g.

The crude material is dissolved with stirring in 910 ml. of ethylene chloride heated to 60° in a water bath (Note 6). The solution is allowed to cool to room temperature, 122 ml. of a saturated aqueous solution of sodium bicarbonate is added to the resulting slurry, and the mixture is stirred for 1 hours (Note 7). The layers are then separated in a separatory funnel, and the ethylene chloride slurry is heated to 60° in a water bath. The resulting solution is filtered through a small cotton plug in a preheated funnel. Absolute ethanol (313 ml.) is added to the filtrate, and the mixture is stored in an icebox overnight while the product crystallizes. The crystals are collected on a filter and washed with 40 ml. of ether. The product is recrystallized by dissolving it in ethylene chloride (3.0 ml. per g. of product) heated to 60° in a water bath (Note 6) and cooling. The yield of white to light pink plates, m.p. 129–130°, is 230–246 g. (68–73%).