Muhammad
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Synthesis and purification of Sodium oleate
I have been trying to make sodium oleate using oleic acid and NaOH solution. After mizing thoroughly a white, oily emulsion forms at the top and a
layer of alkaline water below (excess NaOH). When I heat the cream coloured emulsion it clears out. I dont know where the Sodium oleate is. In the
water or the oil and what test should I perform to confirm the production of Sodium oleate?
Thanks!
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Boffis
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Sodium oleate is soluble in water but it is a soap and therefore a good emulsifying agent by definition. However, if the solution goes clear on
heating and doesn't go cloudy on cooling I think you have made sodium oleate or do you have a clear solution and a layer of oil? In the latter case it
sounds like your oleic is not pure.
Are you trying to obtain sodium oleate as a solid? I can imagine that it is quite difficult to crystallise sodium oleate.
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tsathoggua1
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Could it not be dissolved in isopropanol and salted out?
This despite the polarity of its being an ionic carboxylic acid salt, due to the oleic acid sidechain, its a big, fat greasy zit.
Is it soluble in ether? if it is, then you might try using diisopropyl ether to extract it from the aqueous phase, since DIPE is useful for extracting
polar solutes from polar solvents with which DIPE is immiscible.
You could always try using a very slight excess of bicarbonate, making up a concentrated solution of oleic acid and adding NaHCO3, addition of most of
the stoichiometric quantity of bicarb to the oleic acid, and then when nearly done, adding it a tiny bit at a time, stir, and turn off stirrer, each
time, then add a tiny proportion of bicarbonate, repeat as needed until neutral and CO2 evolution no longer occurs upon addition of a further tiny
quantity of NaHCO3. This would of course leave the last little bit of unreacted bicarbonate present, but given that for the last portion one need
only add sufficient to check for bubbling due to CO2 release, this is miniscule and doubtless of negligible importance.
Also, oleic acid has a double bond, this means it will react with and decolorize bromine water, or dilute iodine solution in alcohol to form oleoyl
bromide/iodide when the halogen adds across the C=C bond, by using a dilute solution of Br2 in H2O, you could do a colorimetric titration.
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UC235
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Sodium oleate is soap. It makes emulsions by definition and has modest water solubility. If you want dry sodium oleate powder, titrate your NaOH and
oleic acid (rarely sold pure, but often as a crude or semi-refined product from hydrolysis of vegetable oil. Disregard if you can obtain a CoA).
Combine them in equimolar proportions in anhydrous ethanol or methanol solvent (which will not foam). Evaporate the solvent to obtain product.
My attempts to free fatty acids from a suspension or solution of soap in water plus acid have always resulted in inordinately greasy hideous
emulsions. The phase separation and tendency for the reaction mix to take on mayo consistency makes it difficult to achieve full neutralization in
aqueous solution. You may be experiencing this in the opposite direction.
[Edited on 18-2-2017 by UC235]
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