[Arnoldus]

Hello

I have a question about the workup of a mesylation reaction. I want to turn a primary alcohol group into a mesylate. Therefore I use MsCl and TEA (and DCM as solvent). When reaction is complete, I do an extraction, first with NaHCO3, then DCM/water.
After reaction I expect the mesylate to be present in the RM, an excess MsCl, excess TEA and triethylammonium chloride. Why should I wash with bicarbonate then? I did this before and it worked perfectly, but when I think about it I can't find an explenation for this extraction...

Can anybody give me a rationale for this?
Thx

[discodermolide]

Presumably to ensure that there is no HCl or source of HCl hanging around.

[Arnoldus]

Presumably to ensure that there is no HCl or source of HCl hanging around.

And that is because mesylate esters are unstable towards acid I guess?

[discodermolide]

Mesylates are just relatively unstable anyway, acids and bases especially as well as nucleophiles.

[Arnoldus]

OK, thanks for the answers! You helped me a lot!

[Arnoldus]

Can you just give me a second opinion on this summary?

In RM:
*mesylate product
*excess TEA (volatile, so we can vac it off)
*excess mesyl chloride (where does this go to actually?)
*triethylammonium chloride (comes in the aqueous phase)
*NaHCO3 is used to neutralise sources of HCl

[discodermolide]

The Mesyl chloride should be hydrolysed by the bicarbonate wash. This gives the Na salt of methanesulfonic acid and CO2 from the HCl and the methanesulfonic acid.

[Arnoldus]

The Mesyl chloride should be hydrolysed by the bicarbonate wash. This gives the Na salt of methanesulfonic acid and CO2 from the HCl and the methanesulfonic acid.

Nice explanation, but I do not see this. How does this work? What is the mechanism for this?

[discodermolide]

The Mesyl chloride should be hydrolysed by the bicarbonate wash. This gives the Na salt of methanesulfonic acid and CO2 from the HCl and the methanesulfonic acid.

Nice explanation, but I do not see this. How does this work? What is the mechanism for this?

Surely methanesulfonyl chloride hydrolyses in water to the methanesulfonic acid and HCl. Both will react with bicarbonate to give CO₂ and the corresponding salts.