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Decrasing solubility of quaternary ammonium compound in water

  1. Mar 8, 2007 #1

    chem_tr

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    Hello,

    I have synthesized a compound with two quaternary ammonium groups and two cyanide groups. I did the reaction in dmf, and after the reaction I poured the reaction medium onto ice-cold water. A little precipitate formed, but I think this is not the compound I want, my compound is still in water.

    Can you recommend a way to decrease the solubility of the quaternary ammonium compound in water? I cannot boil the aqueous solution since I need the cyanide groups. I thought it might be useful if I add some salt with big anions (like potassium phthalate or citrate). What do you think? Additionally, may I use toluene to drive off water as an azeotrope mixture? If so, how can I do it?

    I am waiting for replies, thank you for your interest.
     
  2. jcsd
  3. Mar 8, 2007 #2

    Bystander

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    Cyanide salt? Freeze it and pull a vacuum.

    Cyanide functional groups? Go ahead and boil it --- under reduced pressure if you can swing it --- under N2 if you can't.
     
  4. Mar 8, 2007 #3

    chemisttree

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    If the amount is small (~1-5g) you can trap the dication on a cation exchange column. The weakly acidic Amberlite resins will work. Use the hydrogen form and chase the product off with ammonium chloride. Freeze-drying will probably work best since these compounds tend to be great surfactants and will foam under reduced pressure. Gently warming the freeze dried residue under high vacuum will disproportionate the ammonium chloride away and leave you with your compound as the chloride salt. PF6 or tetraphenyl boron salts will give you less soluble products. The tetraphenyl boron anion will also give you a chromaphore to look at if you analyze by HPLC. Tune to 254 nm.

    For larger amounts, you might want to consider a liquid/liquid extractor using methylene chloride or ether as the extractant. Good for extended, unsupervised work.

    You might also consider exchanging the anion for a flourous anion such as pentafluorobenzoate and use professor Curran's fluorous techniques to purifiy the salt. Ion exchange back to whatever you want and isolate as usual.

    See

    http://www.sigmaaldrich.com/aldrich/acta/al_acta_39_1.pdf

    for the fluorous techniques pioneered by Prof. Dennis Curran.
     
  5. Mar 9, 2007 #4

    chem_tr

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    Thank you for your interest.. I do not have the facility to freeze-dry the compound, so I think I will use high vacuum and distill the water to attempt precipitation.
    By the way, I was away from the lab for some time, and when I returned I saw that a small precipitate formed, maybe due to hydrolysis to the ammonium hydroxide compound.
    Another question appeared in my mind: Do the tetraalkylated ammonium groups give any IR-active peaks, say, at ca. 2400 cm-1?
     
  6. Mar 9, 2007 #5

    chemisttree

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    If you have dry ice and a good vacuum pump and some glassware, you have all you need to perform a freeze drying workup.

    How will you remove the DMF?

    I would seriously consider the fluorous technique.
     
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