2,4-Dinitrobenzenesulfenyl chloride

CAUTION: This reaction should be carried out in a hood behind a safety shield. The product decomposes explosively if heated above 90-100°C . To a 500-ml, three-necked flask equipped with a mechanical stirrer, distillation column, and distillation head is added 100 gm (0.25 mole) of dry 2,4-dinitrophenyl disulfide and 250 ml of ethylene chloride. The contents are heated with an oil bath at 125°C until 30-40 ml of the solvent is collected by distillation. The contents are cooled and the distillation head replaced by a gas inlet and exit tube connected to an alkali trap. Then 0.15 gm (0.002 mole) of Merck "Iron by Hydrogen" powder is added as a catalyst [51a-c], and dry chlorine gas is slowly bubbled into the reaction. In a few minutes, the reaction warms up, and the flask is surrounded with a 20°C water bath. The chlorine gas is bubbled in at such a rate that 18 gm (0.25 mole) is added over a 1-1½-hr period. After this time, the suspended disulfide should gradually disappear, and a clear, amber-red solution results. The flow of chlorine gas is stopped, the solution stirred for 1 hr, filtered through diatomaceous earth, the filtrate aspirated to remove excess chlorine, and then 400 ml of anhydrous ether is added. Within ½ hr, most of the product crystallizes by cooling the flask in an ice-salt-water bath for 3-4 hr. The product is filtered, washed with 100 ml of cold ether, and then dried to afford 70 gm (60%) of brilliant yellow needles, m.p. 95-95.5°C.