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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on October 29, 2020, 09:00:30 PM

Title: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: xshadow on October 29, 2020, 09:00:30 PM
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
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: Babcock_Hall on October 30, 2020, 10:59:00 AM
Have you thought about constitutional isomers?  I am not sure how probable this would be.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: xshadow on October 31, 2020, 06:40:02 AM
Have you thought about constitutional isomers?  I am not sure how probable this would be.

Mhhh
I 'll  think about these...thanks
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: Babcock_Hall on November 02, 2020, 04:10:54 PM
Can you obtain mass spectra on the three peaks?  I see the possibility of two kinds of O-alkylation.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: xshadow on November 02, 2020, 06:24:20 PM
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
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: Babcock_Hall on November 02, 2020, 06:28:45 PM
I see no reason to exclude this possibility without more data.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: AWK on November 03, 2020, 02:14:41 AM
Unsubstituted saccharin.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: wildfyr on November 03, 2020, 09:29:14 AM
I think AWK nailed it. Never forget starting material!
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: xshadow on November 03, 2020, 11:56:53 AM
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
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: Babcock_Hall on November 03, 2020, 12:36:50 PM
Now that you have alternative hypotheses, what should you do next, assuming that you had access to all that you needed?
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: AWK on November 03, 2020, 12:56:26 PM
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.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: wildfyr on November 03, 2020, 01:02:14 PM
@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.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: AWK on November 03, 2020, 02:53:01 PM
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.
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: xshadow on November 05, 2020, 07:09:00 AM
Now that you have alternative hypotheses, what should you do next, assuming that you had access to all that you needed?

NMR/GC MS?

Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: xshadow on November 05, 2020, 07:09:17 AM
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
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: AWK on November 05, 2020, 09:19:14 AM
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).
Title: Re: N/O-ethyl saccharin : GC I get 3 peaks?!
Post by: Babcock_Hall on November 05, 2020, 10:11:56 AM
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.