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I am trying to remove tetrabutylammonium perchlorate (TBAP) from an organic synthesis where TBAP was used as an electrolyte. I am working with compounds containing the amide group. I have used flash column chromatography (FCC) (gradient) but this is laborious.

To give you a better understanding of the experiment this is the path I follow

  1. Once the electrosynthesis of the compounds has completed, the solvents are removed (MeOH & MeCN) in vacuo.
  2. Now for step two, I usually carry out FCC. But I have tried separation using Sodium hydroxide but this did not give me the desired result, the electrolyte was still present after NMR.

Any help would be appreciated.

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  • $\begingroup$ Welcome to Chemistry SE. Do you have references for your procedure? What is the compound you are isolating? $\endgroup$ – Michael Lautman Jun 5 '19 at 11:32
  • $\begingroup$ Hi Michael, Thank you. Reference for the procedure in the paper below “An experimentalist’s guide to electrosynthesis: the Shono oxidation” But to give you an overview of the procedure. In a glass cell the following are added An analyte selected to undergo oxidation, MeOH and MeCN used as solvents and TBAP as electrolyte (does not take part in the reaction). Galvanostatic method (2 electrode) is used to achieve the oxidation A charge is applied until desired coulombs is reached. Right now I am using this method on diethyltoluamide (DEET) $\endgroup$ – Stressed Chem Jun 5 '19 at 11:50
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    $\begingroup$ What are your products soluble in? T-butylammonium perchlorate is insoluble in diethyl ether so you could precipitate it out. $\endgroup$ – Waylander Jun 5 '19 at 11:56
  • $\begingroup$ How about treating the whole with an aqueous solution of sodium metabisulfite to reduce the perchlorate all the way down to chloride. You'll have tetrabutyl ammonium chloride and sodium sulfate. Extract this mixture with an organic solvent to get your 'methoxy DEET' compound. Take care when adding the reducing agent to the oxidising mixture, ensure water is present prior to the addition and cautiously add your metabisulfite solution so that the water acts as a heat sink. Ensure that the reaction is addition rate controlled before doing this at scale. Report back if it works. $\endgroup$ – user1945827 Jun 5 '19 at 13:22
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It's tempting to use phase separation with an aqueous phase, but you're clearly having issues. One option is to evaporate the volatile solvents off, add toluene, cyclohexane or heptane and try water or another additive to boost the ionic strength. The approach using NaOH suggests this may not be successful.

A less conventional approach may be to partition between two organic solvents e.g. acetonitrile or methanol with heptane or methylcyclohexane. The solubility of TBAP appears good enough in alcohols to dissolve well in that phase, while your amide seems more likely to have less polar solvent solubility. Your methanol-MeCN mix may convolute things, so maybe try and strip off the methanol (and likely some MeCN will be lost, but you can top up) or if all else fails, evaporate both solvents and redissolve from scratch.

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