[Babcock_Hall]

We are interested in making vinylsulfones.  One inevitable problem in making a new compound is detecting it by TLC: how do you know a given spot is your product?  I have never had to come up with a new TLC detection system before, but one that detected only vinyl sulfones would be useful.  So far my only idea is to take a nucleophile that is colored and spray a plate.  If the amounts of reagents are just right, the vinyl sulfone would be white, because all of the reagent would react and bleach out.  So far the only possible nucleophile that I can think might work is the TNB anion from the DTNB reaction, which is thionitrobenzoic acid.  The pK_a of TNB is about 5 and it is yellow above that in aqueous solution.  Does anyone have thoughts on the general approach or the specific compound that might work best?

Preliminarily, we think an iodine chamber may be visualizing a phenyl vinyl sulfone, but we are not yet certain.  This particular spot stains with iodine and is also UV-active.

[rolnor]

Pottassiumpermanganate would react with the doublebond and give a brown spot?

[Babcock_Hall]

Funny you should mention that.  We have been playing around with this stain recently for diesters of fumaric and maleic acids, but I don't think that we tried it for the crude reaction mixture yet.  Thanks.

[rolnor]

Maby I deserve a "Molesnack"?

[phth]

I would suggest the Ceric ammonium molbdenate (CAM) stain as a milder alternative to permanganate.  This website has a good list of recipes:
http://www.ochemonline.com/TLC_stains

[rolnor]

The point with permanganate is that it stains doublebonds very well.

[phth]

The point with permanganate is that it stains doublebonds very well.

And CAM stain doesn't? LOL.

[rolnor]

But it has some selectivity for doublebonds, CAM stains almost anything?

[Babcock_Hall]

My experience with advising undergraduate students is that one sometimes spends time and effort troubleshooting or helping them not misinterpret anomalous TLC results.  The problem is that they have not had things go wrong enough times for them to develop an intuition (for lack of a better word) that something is not right.  UV active spots near the solvent front come to mind as one such anomaly that I have seen.

In this case the starting material is a dibromo dimethylester, which does not have a double bond.  My initial thought in this instance was to look for a stain that would be selective for electrophiles, such as vinylsulfones.  That's why I proposed the idea of quenching the TNB anion.  However, I have never come up with a novel TLC stain before, and it seems to me that one has to choose the concentration carefully.

[wildfyr]

What about phosphomolybdic acid stain? It reacts well with conjugated alkenes I believe.


I do think KMnO4 is still the best. It should stain the alkene bright yellow on purple background at RT, whereas other functional groups require some heating to react to give a spot.

[Babcock_Hall]

I think we tried PMA but perhaps not on the product, just the starting materials.  Is CAM ceric ammonium molybdate?  I think we tried that one also, but I had better ask, to be certain.

[MOTOBALL]

Bromosuccinimide--Fluorescein for Sulphur cmpds.

Soln A: 0.035% soln. of N-bromosuccinimide in 1,1,1-trichloroethane

Soln B: prepare 3 mL of a 0.33% soln of fluorescein in 0.1N NaOH; make up to 100 mL with EtOH.

Spray with A; dry at room temp; spray with B

No indication of colour/fluorescence to be expected

See: J.W. Cook, J. Assoc. Off. Agr Chemists 37, 983 (1954)

NOTE !! There is a similar spray (in gl. AcOH) for lipids; see A. Popov, V. Gadeva, J. Chromatog. 16, 256 (1964) and J. Micev, A. Popov, L. Nedelceva, J. Chromatog. 24, 432 (1966)

Good Luck and please let us know the outcome.

[rolnor]

I wonder if this reagent really gives a spot with sulfones? Sulfides and sulfoxides would.