Bender84
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silica in organic solvents
Hello,
I'm trying to estimate silica content (as silicic acid) in organic solvent, which is 2-ethylhexanol (2-EH). The test I'm using is the photometric
Merck test for determination of silica as silicic acid (in sulfuric solution silicate ions react with molybdate ions to form a yellow heteropoly
acid. This is reduced to silicomolybdenum blue that is determined photometrically).
The problem is that this test is dedicated to water solutions only. I tried to make a water extract from the aforementioned solvent but the results I
got were unrepeatable and inconclusive. Also when I do a second extraction with water of the same sample, I got a bit different result, so it is not
like the whole silica - if present - is extracted from the solvent at the first approach (the 2-EH samples with distiled water in 1:1 ratio were
shaked for 20 min).
My question is: having the nature of silica in mind, is it posssible that it is present in 2-ethylhexanol? Also can any of You recommend an approach
to tackle this problem, i.e. how to estimate the silica content in 2-EH (if it makes sense to do so)?
Regards.
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Sulaiman
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could you evaporate (or distill off) the solvent to dryness then check for residue by weight ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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UC235
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Why do you expect silica in 2-ethylhexanol? Solubility should be roughly zero. Phosophomolybdic acid also readily forms from trace phosphate and is
reduced to a bright blue compound. Are you sure you're not detecting this as contamination?
[Edited on 23-5-2020 by UC235]
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Bender84
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Thanks for the answer!
The idea of 2-EH contaminated with silica came from a nitration tests where at the end of the reaction, apart from the reaction mixture which is 2-EHN
and spent acids (sulphuric acid, nitric acid and water), I got a white, gelitnous residue. I centrifuged the residue, washed it with water, dried in
oven and analyzed using FTIR. The spectrum was identified as SiO2. I am sceptical about this, but my supervisors are quite fixed on the idea that it
is indeed silica or some sort of silicate present in the solvent.The problem occured when I tried to nitrate 2-EH from different manufacturer, so the
only thing that has changed in the whole procedure is the alcohol. Still, I don't get repetable results when I am using the Merck test and the whole
concept seems a bit far-fetched.
I tried to evaporate the solvent but didn't find any silica. Also I could not analyze the residue by disolving it in water due the fact that the Merck
test should be done using plastic utensils and I had to evaporate the solvent on a watch glass. I will check the phosphates, though. Thank you!
Regards.
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Bedlasky
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Quote: Originally posted by UC235  | Why do you expect silica in 2-ethylhexanol? Solubility should be roughly zero. Phosophomolybdic acid also readily forms from trace phosphate and is
reduced to a bright blue compound. Are you sure you're not detecting this as contamination?
[Edited on 23-5-2020 by UC235] |
I use these Merck tests in job for detecting silicates in waters and these waters also contains phosphates. There isn't any phosphate interference.
These reductions of molybdates and heteromolybdates strongly depend on pH. Molybdates, phosphomolybdates, silicomolybdates - each of this anions need
different pH for reduction.
Bender84: Try water solution with Merk reagents (without reducing agent) - it should extract silicates from alcohol if there are present.
Silicomolybdates are very stable complexes. After extraction just add reducing agent.
[Edited on 23-5-2020 by Bedlasky]
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