Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: SamMcG on June 29, 2015, 06:27:45 PM
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Hi,
I need help with the identification tests for PEG. I haven't been able to find any information regarding the chemical reactions taking place ie. I need to know what each of these tests is identifying and the mechanisms of action. I also need to know if these tests are specific to any molecular weight, I'm assuming they're non specific as they're listed in the EP under macrogol with no defined MW (viscosity testing is used to ID the molecular weight). Any information, or where I could find more information is appreciated. Regards.
The ID tests as per EP:
B. To 1 g in a test-tube add 0.5 ml of sulphuric acid R, close
the test-tube with a stopper fitted with a bent delivery
tube and heat until white fumes are evolved. Collect the
fumes via the delivery tube into 1 ml of mercuric chloride
solution R. An abundant white, crystalline precipitate
is formed.
C. To 0.1 g add 0.1 g of potassium thiocyanate R and 0.1 g
of cobalt nitrate R and mix thoroughly with a glass rod.
Add 5 ml of methylene chloride R and shake. The liquid
phase becomes blue.
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B). Hot H2SO4 oxidizes PEG to oxyacetaledehyde terminated polymer chain and by its turn is reduced to gaseous SO2. Collected SO2 vapors form H2SO3 in aqueous medium. Aqueous hydrogen sulfite reacts with Hg2+ to form, in the absence of excess HSO3-, the Hg[SO3]2- complex. Besides, HgSO3 decomposes by an intramolecular redox reaction to metallic mercury that precipitates together with HgHSO3.
-CH2CH2OH + H2SO4 → - CH2CH=O + SO3↑ + H2O
SO3 + H2O → H2SO3 → H+ + HSO3-
Hg2+ + HSO3- → HgHSO3 + H+
HgHSO3 + H2O → Hg + H2SO4
Hg + HgHSO3 → Hg.HgHSO3↓
http://pubs.acs.org/doi/abs/10.1021/jp994268s
C). Cobalt isocyanate which is formed has a blue coloration and is chelated with PEG and thus, it is soluble in dichloromethane.
CO2+ + 2SCN- → Co(SCN)2 → [(-OCH2CH2OH)2Co](SCN)2
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Thank you very much! Sorry for taking so long to reply, I had forgotten I made a thread and gave up looking online :)
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Hello Can you please share the EP pages mentioning the polyethylene glycol ID test.
Thank you.
Alpana
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There is a typo error of sulfur dioxide in my post. The right is:
-CH2CH2OH + H2SO4 → - CH2CH=O + SO2↑ + H2O
SO2 + H2O → H2SO3 → H+ + HSO3-
etc.
Sorry!
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Hello Can you please share the EP pages mentioning the polyethylene glycol ID test.
Thank you.
Alpana
No, the pharmacopeias are copyrighted and we don't share copyrighted materials. Furthermore, if you expect to use in a manufactured pharmaceutical the PEG you're testing, you'll have to have a subscribed copy on-hand. Failure to do that is a violation.
Now if you're just curious, you can find references online that give you the procedure, for example, this thread itself.
[EDIT] changed wording in italics