A solution of
phosphorus trichloride (137.3 g., 1.0 mole) in
1.5 l. of dry ether (Note
1) is added to a
3-l., three-necked, round-bottomed flask equipped with an
efficient stirrer,
thermometer, a
gas-inlet tube (Note
2), and a
reflux condenser vented through a
nitrogen reservoir (a T-tube under slight positive nitrogen pressure) into a
well-functioning hood (Note
3). The flask is cooled in an
ice bath to 0–5°, and an excess of anhydrous
dimethylamine (Note
4) is introduced at such a rate that the temperature does not exceed 15° The addition requires about 3–4 hours. At the end of this period the flask contains the white stirrable slurry of the
amine hydrochloride and the ethereal solution of the
phosphorous triamide (Note
5). The reaction mixture is allowed to warm to room temperature overnight while still being protected by
nitrogen. Filtration of the slurry and thorough washing of the filter cake with three
100-ml. portions of dry ether afford
dimethylamine hydrochloride, quantitatively (Note
6). The clear filtrate is concentrated on a
rotary evaporator connected to a
water aspirator in a bath not exceeding 40° to give
152–154 g. (
94–95%) of
hexamethylphosphorous triamide as a light yellow oil. The product can be purified by distillation at atmospheric pressure, b.p.
162–4°, or under reduced pressure, b.p.
49–51° (12 mm.),
n25D 1.4636 (Note
7).
Hexamethylphosphorous triamide is best stored in a
nitrogen atmosphere (Note
8).