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Author: Subject: Testing phase-transfer catalysts.
FrankMartin
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[*] posted on 4-6-2010 at 20:01
Testing phase-transfer catalysts.


I have some TetraButylAmmoniumFluoride, TBAChloride, TBABromide, TBAIodide. Also PEG400, 18C6, and Aliquat336.

In assessing these catalysts for a reaction, is it a good start to check the transfer of permanganate anion into the reaction solvent(s), (gives a purple colour)? Some of the above catalysts are not soluble in heptane and similar paraffinics?

E.g: TBAF, & TBAB will not dissolve in paraffinics and permanganate anion is not transferred into them. Should these catalysts then be excluded from consideration? What about a blend of solvents sufficient to dissolve the catalysts and produce in them the permanganate purple anion.

I am thinking of saving costs.

FM
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JohnWW
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[*] posted on 4-6-2010 at 20:23


Because of its charge and polarity of Mn-O bonds, permanganate(VII) is soluble only in water, and highly polar organic solvents (such as aliphatic ethers and ketones) which are not easily oxidized or decomposed by it. These would be the same solvents in which one would expect tetrabutylammonium halides, also ionic, to be soluble, although due to the size of the organic groups on the cation their solubility in water may be limited.
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ThatchemistKid
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[*] posted on 4-6-2010 at 21:01


I have read that 18-crown-6 ether specifically chelates the potassium ion and has been used to make a potassium permanganate solution in benzene.
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Nicodem
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[*] posted on 5-6-2010 at 02:33


https://www.sciencemadness.org/whisper/viewthread.php?tid=11...
https://www.sciencemadness.org/whisper/viewthread.php?tid=94...
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Barium
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[*] posted on 5-6-2010 at 06:16


FrankMartin: Use toluene, xylene or DCM in your trials instead. The lower alkanes are shitty solvents in general.

JohnWW: Using PTC the permanganate ion can be transferred into various organic solvents, e.g. toluene and DCM.
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peach
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[*] posted on 22-6-2010 at 04:14


Has anyone seen references for swapping the halides on TBAB to TBAI? I have TBAB and want to transfer iodide ions in an organic system, so I'm not sure if the bromide will give up it's bromide's in favor of iodides in that case. I could also do without the bromides / bromine floating around near the double bonds of my substrate if possible, even though it'll only be in minute quantities.

[Edited on 22-6-2010 by peach]
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jon
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[*] posted on 7-7-2010 at 16:37


from what my dumb ass has read in the past it's a simple matter of chucking some alkali iodide in the mix but yes it works.
oh wait i had to smack my forehead to reboot, it went something like this, they were n-alkylating an amine and tbab was used the alkylating agent was an alkylbromide secondary.
so to improve the yields of the reaction NaI was tossed in which swaped with the tbab to give tbai this transferred to the alkylbromide to yeild the iodide once the sn2 was complete the alkali iodide was recycled because the reaction was done in a basic enviroment so the HI kicked off was nuetralized and water taken up in mol seives.
so a stoich equiv was'nt neccessary.


[Edited on 8-7-2010 by jon]

[Edited on 8-7-2010 by jon]
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peach
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[*] posted on 8-7-2010 at 08:37


Good thinking, I'll try making some TBAI up tomorrow. The MP of TBAI is about 50C higher than TBAB, so I should be able to identify the two using that.
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jon
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[*] posted on 8-7-2010 at 12:54


use alcohol as the solvent.
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kookychemist
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biggrin.gif posted on 28-8-2011 at 22:07
testing a quaternary phosphonium salt as a PTC


Being my first post to the forum, I hope i'm doin' it right.

I'm new to heterogeneous reactions and reactions involving PTC's. With many solvent systems unavailable to the amateur chemist I'm very much interested in experimenting with PTC's for reactions between immiscible solvents.

The only over the counter PTC I've found in decent purity and with N-alkyl chains long enough to withstand Hoffman rearrangement, is Didecyl Dimethyl Ammonium Chloride and I've read that these PTC's tend to be poor PTC's because of micelle formation rather than actually carrying ionic species into the organic layer.

I've read that quaternary phosphonium salts may also be used as PTC's, and while it is not an OTC chemical I just happen to HAVE about 100g benzyltriphenylphosphonium chloride, I know it is used for the Wittig rxn and i'm sure its probably a waste to use it as a PTC, but in a pinch it might be a useful to re purpose it. What would be a good solvent system to test the salts ability to function as a PTC and does anyone have experience using a phosphonium salt as a PTC? I've also read that they are sometimes very difficult to seperate from rxn products, I'd love to hear some suggestions.

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Nicodem
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[*] posted on 29-8-2011 at 13:18


Benzyltriphenylphosphonium chloride might work for some reactions, but since you don't specify your intended use, it is not possible to give a useful answer. It is probably useless for reactions under strongly basic conditions as it will slowly get hydrolysed to toluene and triphenylphosphine oxide.

The easily obtainable didecyldimethylammonium chloride could likewise be used for various reactions. I don't think micelle formation would be an issue with this one. I remember at least one example where this ammonium salt was successfully used for O-benzylation of eugenol with benzyl chloride under solventless conditions. This was described in one post I read a few years ago at the Hyperlab.info forum (try their forum search engine for "BZOMA" as keyword, as that was the code for the target compound - the post was in English as even I understood it). I think K2CO3 was used as the base, if I still remember correctly. There might be other examples from other amateurs, but it is highly unlikely to find any in the scientific literature, because researchers use standard PTC such as tetrabutylammonium salts (at least I do).




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