Organic Syntheses, CV 4, 950
TRICHLOROMETHYLPHOSPHONYL DICHLORIDE
Submitted by Kenneth C. Kennard and Cliff S. Hamilton
1.
Checked by John C. Sheehan and J. L. Yeh.
1. Procedure
Caution! This preparation should be conducted in a hood.
In a
2-l. round-bottomed three-necked flask, fitted with an
efficient reflux condenser,
mechanical stirrer, and
dropping funnel (Note
1), are placed
133.3 g. (1 mole) of anhydrous powdered aluminum chloride,
137.4 g. (1 mole) of phosphorus trichloride, and
184.6 g. (1.2 moles) of carbon tetrachloride (Note
2). The reactants are stirred slowly until they are thoroughly mixed, and then heat is applied carefully until the reaction begins. At this point the liquid boils vigorously, and the reaction mixture becomes thicker so that faster stirring is necessary. Finally, the stirrer is stopped when the mixture becomes solid. After the reaction has cooled for 30 minutes,
1 l. of methylene chloride is run into the flask (Note
3), and the solvent is stirred vigorously until the solid is finely suspended (Note
4). The reflux condenser is replaced by a low-temperature
thermometer which dips into the reaction mixture, the suspension is cooled in a Dry Ice-acetone bath, and the temperature is kept at −10° to −20° as distilled water (180 g., 10 moles) is added dropwise with vigorous stirring over a period of about 25 minutes (Note
5). After the water addition is complete, stirring is continued for 15 minutes without the cold bath.
The apparatus is dismantled, and the reaction mixture is filtered quickly by suction through a 1.5-cm. layer of filter aid on an
11-cm. Büchner funnel placed on a
2-l. filter flask. The filter cake is pressed down well and washed with three
50-ml. portions of methylene chloride. The filtrate is immediately protected from moisture by
calcium chloride tubes, and the solvent is removed by distillation from a
2-l. flask. After the solution has been concentrated to about 225 ml., the hot liquid is poured into a suitable
container (Note
6), and the remaining solvent is removed under reduced pressure (Note
7). The yield is
192–199 g. (
81–84%) of a white, crystalline solid which melts at
155–156°.
2. Notes
1. The equipment is dried and protected from atmospheric moisture by
calcium chloride tubes.
2. It is important that the reactants are pure; otherwise the complex is colored. If the containers are freshly opened,
C.P. reagents are satisfactory.
4. If the solid adheres to the flask, the flask is heated lightly with a free flame to loosen it.
5. Vigorous stirring is necessary to prevent caking of the
aluminum chloride hydrate and to prevent localized hydrolysis. The checkers found that exactly 7 moles of water gave a somewhat improved yield, but handling was more difficult.
6. The submitters used a
500-ml. round-bottomed wide-mouthed flask.
7. The product may be warmed to aid solvent removal, but it is decomposed by prolonged heating above 60°.
3. Discussion
The
aluminum chloride process
2,3 is a general method for the preparation of alkylphosphonyl dichlorides.
Trichloromethylphosphonyl dichloride has been made also by the chlorination of
chloromethyldichlorophosphonic dichloride in the presence of light or other catalysts
4 and by the reaction of
tetrachloro(trichloromethyl)phosphorane with
sulfur dioxide.
5 The procedure described here is essentially that of Kennard and Hamilton
6 and is based on the procedure of Kinnear and Perren.
2
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