[darkdevil]

Hi,

I am trying to make a triphenylphosphonium salt (a Wittig reagent) from an electron rich molecule that has an EDOT moiety

The reaction failed to give out any product as I tried the following conditions:
1) with acetone as solvent and refluxed for 1 day (No product in TLC, only starting materials)
2) with toluene as solvent and refluxed for a hour (No product and EDOT starts to decompose)
3) with xylene as solvent and refluxed for a hour (No product and EDOT starts to decompose to give out brown polythiophenes I guess)
4) with no solvent but seems there is no reaction


I tried to do the same reaction with triphenylphosphine and benzyl chloride in refluxing acetone and the yield is over 80% and clean, since the salt is not soluble in acetone.

I also read some literature about phosphonium salt preparation that primary alkyl halides react slowly and takes much longer reaction time (benzyl works best) .I wonder if this is a dead end for making this salt or there is another way to make the phosphonium salt? As far as I know, the reaction is an SN2 reaction, the electrophile here is an electron rich primary halide compound that makes it even slower.
I want to add some potassium iodide to it and see if it can do something like halide exchange during the reaction. Do you think this will work? THanks!!

[phth]

It's not the same molecule as benzyl chloride you can't compare them because there are several differences.  The oxygens are pulling on the chlroine bond in the way that the dipoles allign anti thus stabilizing the bond in the non polar solvent choices you chose.  You are trying to generate ions from neutral things in a non-polar solvent.  That means the reaction is up hill.  The substrate is labile, so that overtaking the SN2 reaction.  You can use another ylide equivalent.  For example ^-SMe will form a neutral desired product and a salt.  Stabilized ylides: RSO₂Ph(or just tosylate), HWE.  I would put it in a glyme solvent that is dried beforehand. 

[opsomath]

That is kind of a crappy SN2 electrophile. Things you can do:

• Add 10% potassium iodide or sodium iodide to refluxing acetone (DRY) as a catalyst
• Completely exchange the chloride out for a better leaving group using dry acetone using a Finkelstein reaction
• Move to a more polar, higher boiling solvent such as DMSO or HMPA. Degas using nitrogen and make sure it's dry to ensure your stuff is stable.