Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on October 29, 2020, 09:00:30 PM
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Hi
I synthesized N/O ethyl saccharin and then I've dome a gas chromatograpy...but I get 3 peak instead of two.
The third peak which molecule(impurity) could it be?
(https://i.imgur.com/hUB3jMz.jpg)
The first peak eluited is the N-ethyl saccharin
I don't know which peak is the O-ethyl saccharin
..the one in the middle or the last one?
Ps: I use 10mmol iodoethane with 10 mmol sodium saccharin in DMF.
After the reaction ended I washed with water
Thanks
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Have you thought about constitutional isomers? I am not sure how probable this would be.
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Have you thought about constitutional isomers? I am not sure how probable this would be.
Mhhh
I 'll think about these...thanks
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Can you obtain mass spectra on the three peaks? I see the possibility of two kinds of O-alkylation.
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Can you obtain mass spectra on the three peaks? I see the possibility of two kinds of O-alkylation.
Can t now :(
Do you mean also the alkylation through S=O groups?
Thanks
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I see no reason to exclude this possibility without more data.
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Unsubstituted saccharin.
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I think AWK nailed it. Never forget starting material!
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But does sodium saccharin have a lot higher boiling point (is a salt)than the two products?
Or is not too much different because is in a solvent (not a solid salt)?
Thanks
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Now that you have alternative hypotheses, what should you do next, assuming that you had access to all that you needed?
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Sodium saccharin is obviously non-volatile at GC. Saccharin is an acid with a strength comparable to that of oxalic acid. If sodium saccharin was present in the reaction mixture, on washing with water, it could have significantly hydrolyzed and a much less water-soluble saccharin was formed, which had only 2 degrees C higher boiling point than its O-ethyl derivative.
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@AWK I don't like saying the sodium salt hydrolyzed. That implies the N-S bond or N-C cleaving to me. Better to say it acid/base equilibration occurred under aqueous conditions.
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Saccharin is a very stable compound.
I do not believe in the possibility of breaking the S-N or C-N bond under the conditions of synthesis and isolation of the alkylation product. The saccharin in the GC sample may only come from an incomplete reaction or from degradation of the O-ethyl derivative upon injection due to traces of water present in the gas chromatographic sample.
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Now that you have alternative hypotheses, what should you do next, assuming that you had access to all that you needed?
NMR/GC MS?
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Sodium saccharin is obviously non-volatile at GC. Saccharin is an acid with a strength comparable to that of oxalic acid. If sodium saccharin was present in the reaction mixture, on washing with water, it could have significantly hydrolyzed and a much less water-soluble saccharin was formed, which had only 2 degrees C higher boiling point than its O-ethyl derivative.
understand!
thanks
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NMR will allow you to find the ratio of N-ethyl to O-ethyl derivatives in the crude reaction product, and GC-MS to identify these three peaks (the O-ethyl derivative partially isomerizes at temperatures above 200C).
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Now that you have alternative hypotheses, what should you do next, assuming that you had access to all that you needed?
NMR/GC MS?
I suspect that either one would work.