[Zensation]

I read that TBAI is great to use in substitution reactions that use Alkyl Chlorides and NaOH, since the Alkyl Chloride is converted to an Alkyl Iodide intermediate which can readily react with a present nucleophile. This is supposed to be very effective.

I also read much about how the Iodide ion acts as a catalyst poison and can completely stop reactions from occurring by tying up the quaternary ammonium cation. If an alkyl chloride, turned iodide, reacts with a NaOH nucleophile, then NaI would be formed, leaving TBAI as TBACl. Would this not "poison'' the TBACl? Or is sodium chloride formed instead of sodium iodide, in spite of the hydroxide being attacked by the intermediate alkyl iodide?

I'm just confused on how Iodide can be a phase transfer catalyst poison, yet iodide quaternary ammonium salts be some of the most effective PTC by nature of halogen exchange with alkyl chlorides/bromides.

[discodermolide]

Somehow I don't think that iodide is a poison for phase transfer catalysts. Do you have a reference for this?
It may well be a poison for hydrogenation catalysts.

[Zensation]

https://www.google.com/search?q=iodide+phase+transfer+catalyst+poison&oq=iodide+phase+transfer+catalyst+poison

I read over some reactions that require PTC in the presence of iodide ions reduced the yields to nearly 10-20%.

If TBAI can indeed act as a good catalyst for reactions involving alkyl chlorides and NaOH(to deprotonate the aq. substrate), then the only explanation I can think of is that the iodide in TBAI never really leaves the quat but enables an alkyl iodide to exist in equilibrium with the initial alkyl chloride, causing the substitution to go forth as it normally would as if the NaOH nucleophile was reacting directly with the alkyl chloride... though I have no evidence for this.

[orgopete]

Why not tell us the reaction? I can think of various ways the yield might change. It needn't be a poison, rather emergence of by-products.

[Zensation]

No specific reaction comes to mind other than the general transfer of NaOH enolates to the organic phase.

I don't think by-products would be much of an issue. I am just looking into how to maximize the speed of such [substitution] reactions through minimizing required temperature and reaction time by choosing an appropriate PTC. When alkyl chlorides are in play, which they often are due to their low cost, the intermediate alkyl halide that is generated by the PTC will greatly effect reaction times and efficiencies. Using an alkyl chloride + iodide-ptc should be have similarly to using an alkyl iodide, except, with less side reactions such as hydrolysis.

I did recall reading up that Iodide in the right molar quantity can act as a cocatalyst, such as NaI with TBAB/TBACl/CTAB, etc. So maybe that is what is going on.

IIRC, Iodide was said to be a catalyst poison because if there is too much of it, it ties up the PTC making it ineffective because of how rapidly iodide can leave and reattach to the catalyst. Though I wish to understand the mechanics behind what makes it a poison vs a cocatalyst.