A 1-l. round-bottomed flask is equipped with an internal thermometer, a sealed stirrer, and a reflux condenser, the upper end of which is protected with a calcium chloride drying tube. In this flask are placed 307 g. (2 moles) of dry, pulverized betaine hydrochloride (Note 1) and 285 g. (174 ml., 2.4 moles) of thionyl chloride. The mixture is stirred and heated slowly. When the internal temperature reaches 68° copious evolution of sulfur dioxide and hydrogen chloride occurs, and the mass becomes pasty. The temperature is maintained with stirring at 68–70° for 1.5 hours (Note 2).

Warm (80°) dry toluene (150 ml.) is added to the melt, and stirring is continued for 5 minutes. The entire mass is quickly poured into a dry beaker (Note 3) and slowly stirred, manually, until the entire mass has crystallized (Note 4). The cool toluene is decanted rapidly, and 150 ml. of warm toluene is added. The mixture is heated sufficiently to melt the crystals (about 68°), then allowed to cool again with stirring. The toluene is decanted once more, and 150 ml. of hot (60°) dry benzene is added. The mass is melted once more and cooled with stirring. The crystalline mass, with the benzene layer still covering it, is transferred rapidly to a Büchner funnel sufficiently large to hold all the contents of the beaker. The funnel is immediately covered with a rubber diaphragm, and suction is applied (Note 5). The crystals are quickly covered with 150 ml. of dry methylene chloride, dried with suction, and quickly transferred into a glass vacuum oven at 50° (Note 6). The yield of N-chlorobetainyl chloride is 337–344 g. (98–100%) of 98–100% purity if moisture was rigorously excluded (Note 7).