Synthesis of phosphonate salt not working I have tried four times in the past few weeks to synthesise 2-ethoxyvinyl phosphonyl dichloride by reacting ethyl vinyl ether with phosphorus pentachloride in toluene. 

I have been following the literature procedure (see below) successfully up to the point where it says that I need to bubble sulfur dioxide through the reaction mixture - at which point it will turn clear. The reaction turns a pale yellow color; the next step is where I'm at my wit's end - the literature says to obtain the 2-ethoxyvinyl phosphonyl dichloride by direct distillation and every time I've tried this, it's resulted in a black, opaque solution. The literature does not say what color the final product is although my supervisor has said that it should be a yellow oil. I'm thinking that it could have decomposed upon heating, although the boiling point according to the literature is 142 &deg;C and the bp of toluene is 110. Previously I tried the same reaction in $\ce{CCl4}$, which distilled off at 76 &deg;C and also turned black. 

I would really appreciate help on this, since it's part of my final year project and I only have a handful of lab sessions left to finish this. Thank you in advance! (Also, I've attached an image of the literature procedure below if it might be helpful).


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Looking at the procedure (and considering the structure of the desired product) it appears that its boiling point is 142C at 27 mm (not at atmospheric pressure). So you should try a vacuum distillation to purify your product. Heating it to try to distil it at 1 atm is probably causing decomposition. Also, be sure to protect the reaction mixture and the final product from atmospheric moisture.