Dimethylamino dichlorophosphine

The apparatus shown in Fig. 16 is set up in the fume hood. The equipment is flushed with dry nitrogen, then a 200-mI. portion (314.8 g., 2.29 mols) of phosphorus trichloride is placed in the 2-1. reaction flask. The flask is partially immersed in the Dry Ice-isopropyl alcohol bath the clamp to the alkylamine container is opened and a stream of dry nitrogen is passed through the system at a rate of about 30 cc./noinute measured at S.T.P. The nitrogen stream sweeps the anhydrous amine (200 g.) from the bottle into the reactor. The amine usually condenses on one of the two cold fingers of the reactor and drips into the chilled stirred phosphorus trichloride solution. Finely divided dimethylammonium chloride precipitates immediately. 

The anhydrous dimethylamine may be obtained in convenient 100-g. bottles from Eastman Organic Chemicals, or any other source of pure dimethylamine may be utilized. The nitrogen flow rate is important. If the flow rate is too high, large amounts of the amine hydrochloride will be entrained, and the outlet tube will be blocked. At still higher flow rates, amine may pass through the reactor unchanged and low yields will result. 

The addition of dimethylamine is usually completed within 3 hours. The reaction mixture is then stirred under nitrogen for an additional 3 hours while the system warms slowly to room temperature. The reflux condenser on the exit side (the right) of the reactor is quickly replaced by a distillation apparatus suitable for fractionation. The reaction mixture is then distilled under dry nitrogen at a pressure of 1 atmosphere. The fraction boiling at 149 to 151°/745 mm. is collected as product. In a typical experiment, this fraction weighed 304.8 g. or 94% of theory based on the dimethylamine used. Anal. Calcd. for (CH3)2NPCl2 C, 16.46 H, 4.14 N, 9.60 Cl. 48.58. Found C, 16.39 H, 4.16 N, 9.30 Cl, 48.68. 

The product is a water-white liquid with an obnoxious odor. It boils at 150°/760 mm. It is reactive toward water and amines, and reacts slowly with atmospheric oxygen. On long standing, it deposits small amounts of dimethylammonium chloride. 

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