The reaction is conducted in a
500-ml. three-necked flask equipped with a sealed
mechanical stirrer, a
dropping funnel, and a
reflux condenser carrying a
drying tube. The flask is flushed with dry
nitrogen, and
104 g. (0.50 mole) of phosphorous pentachloride in
150 ml. of dry benzene is added. The mixture is cooled in an
ice bath (Note
1) and stirred while a solution of
26 g. (0.25 mole) of styrene in
50 ml. of dry benzene is added through the dropping funnel during a period of 30 minutes. A dense crystalline solid begins to form immediately, and after the addition is completed the mixture is stirred for 30 minutes at room temperature. The dropping funnel is replaced by a gas-inlet tube which is connected to a cylinder of
sulfur dioxide through a
wash bottle containing concentrated
sulfuric acid.
Sulfur dioxide is bubbled through the stirred mixture until all the precipitate is dissolved. The mildly exothermic reaction is controlled by occasionally cooling the reactants with an ice bath. The
benzene solvent is removed from the clear solution under reduced pressure, and the residue is distilled at reduced pressure from a
Claisen flask with Vigreux indentations. The yield of
styrylphosphonic dichloride is
49–52 g. (
89–94%), b.p.
107–110° (0.2 mm.). The distillate solidifies during or after the distillation, m.p.
71–72°.