Triphenyl trichloromethyl phosphonium Chloride

Triphenyl(trichloromethyl)phosphonium chloride and (dichloromethylene)tri-phenylphosphorane are important intermediates in the reaction system triphenyl-phosphine/carbon tetrachloride. Solutions of (dichloromethylene)triphenyl-phosphorane, which is a convenient Wittig reagent, were first prepared by the addition of dichlorocarbene to triphenylphosphine in chloroform. However, the ylide could not be separated without degradation caused by the reaction medium. 

The method of preparation described here is based on the dechlorination of triphenyl(trichloromethyl)phosphonium chloride in benzene, which makes the isolation of the (dichloromethylene)triphenylphosphorane possible without decomposition.  

A 1000-mL round-bottomed flask equipped with a side-arm gas inlet and a large magnetic stirring bar is flushed with nitrogen. Triphenylphosphine [Aldrich] (105 g, 0.4 mole), anhydrous carbon tetrachloride (400 mL), and dry acetonitrile (200 mL) are placed in the flask. Carbon tetrachloride and acetonitrile are dried 

After stirring for an additional hour, the solid is collected by filtration through a Schlenk filter tube, washed with 50 mL of dry benzene and 50 mL of dry diethyl ether, and dried under vacuum. Benzene and diethyl ether should be heated at reflux over sodium metal. The yield of crude [PhjI —CCljjCl is approximately 40 g. The product must be recrystallized before it is used as a starting material for Part B. 

For recrystallization, the water-sensitive compound is transferred under anhydrous conditions into a 1000-mL round-bottomed flask and is dissolved in approximately 100 mL of dry dichloromethane. Dichloromethane is dried by stirring with P4O10 and distilling before use. Dry diethyl ether, which is contained in a pressure-equalizing dropping funnel, is added in small portions until the product starts to separate. After 3 hr under an inert atmosphere, recrystallization is complete and the white solid material is separated by filtration through a Schlenk filter tube and dried under vacuum. Yield 29 g (17.4%) mp 171-180 (dec.). 

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