[wereworm73]

Wouldn't the recombination side reaction go like this?

2 ^-:CCl₃ ---> 2 :CCl₂ + 2 Cl^- ----> Cl₂C=CCl₂

[HP]

Yah, if dichlorocarbene generated as you show then tetrachlorethylene possible product of its recombination i think...

[wereworm73]

After reading up on Appel reactions a bit, it looks like CCl₄ would work just as well as CBr₄.  Some thoughts on this, though:

I definitely like the idea of having a relatively mild way of converting something into a halide, but I think there would be a few problems.

Because PPh₃/CCl₄ forms a trichlorocarbanion, I think it would be best if the concentration of PPh₃/CCl₄ was kept low compared to OH-(CH₂CH₂-O-CH₂CH₂-O-)_n-CH₂CH₂Cl (if my "X" group is going to be hydroxide).  Since ^-:CCl₃ can spontaneously form :CCl₂, it would be important to give an ample opportunity for the carbanion to deprotonate the OH- group before it's allowed to become a carbene.  I'm also concerned that the carbanion may do a nucleophilic attack on the chloro- group on my target molecule and form an unwanted side product.


I'm also wondering if the PPh₃ would react directly with the chloro group on OH-(CH₂CH₂-O-CH₂CH₂-O-)_n-CH₂CH₂Cl as well as CCl₄.  If it does, then the resulting phosphonium salt would probably end up dimerizing my product there.  True, there's fewer halogens withdrawing electron density from the carbon on this molecule than there is on CCl₄, but is that going to be much of a factor?