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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Mr.wdaly on February 06, 2020, 12:46:25 PM

Title: thionation
Post by: Mr.wdaly on February 06, 2020, 12:46:25 PM

I am trying to monothionate ethyl benzoate in toluene using lawessons reagent.

Following some literature methods I still can't seem to get it to work or at least IR and proton NMR are practically identical to the starting material.

I thought the C=S would give a better indication that it has formed.

Any advise and help is greatly appreciated.

Title: Re: thionation
Post by: pgk on February 06, 2020, 02:35:50 PM

1). The 1H-NMR and IR spectra are not identical but they are slightly different. To detail:
1H-NMR: Methylene peak may be slightly shifted, which makes it looking like identical with the starting material. 
IR: C=S absorbs at 1200-1050 cm-1, which is the zone of C-O absorption that makes difficult to identify a thiocarbonyl compound in mixture with an ester. Or even impossible, if peaks overlapping occurs.
So, you superpose the corresponding spectra of the product and the starting material, look at them towards a light source and search for slight differences.
2). You can also try UV or/and 13C-NMR spectroscopy.
3). But first of all, did TLC show any formation of your product?   

Title: Re: thionation
Post by: rolnor on February 06, 2020, 04:02:21 PM

TLC is great in this case, the product will react strongly if you dipp the plate in KMnO4 solution, the startingmaterial will not. You will have to put the Lawesson reagent as reference also on the plate, this material is also UV-absorbing. Lawesson is moisture sensitive so old cans are no good.

Title: Re: thionation
Post by: wildfyr on February 08, 2020, 05:58:55 PM

Also.... Doesn't it stink?

Title: Re: thionation
Post by: rolnor on February 09, 2020, 04:48:55 AM

Yes, it stinks! Fumehood is good.