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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Markov on March 04, 2009, 04:53:41 AM

Title: practical capture of CH3SH / methanethiol / methyl mercaptane?
Post by: Markov on March 04, 2009, 04:53:41 AM

I am carrying out a thiomethylation of an aromatic ring, using dimethyl disulphide (MeS-SMe) as the electrophile to react with an aryllithium compound. The released methanethiolate anion is captured by adding methyl acrylate (the Michael adduct of which is then hydrolysed and washed into water).
 
The current method works fine, except I end up with too much polymeric material in the isolated product. I assume the acrylate plays a big part in producing the polymerics.

Anybody who has a smarter and cleaner way of trapping methylthiolate?

Thanks,
/Markov

Title: Re: practical capture of CH3SH / methanethiol / methyl mercaptane?
Post by: sjb on March 04, 2009, 06:32:47 AM

How soluble is your required compound in water? Can you reprotonate the thiolate and partition it between organic and aqueous, then strip the aqueous and oxidatively form the sulfonic acid or something (probably less volatile)

S

Title: Re: practical capture of CH3SH / methanethiol / methyl mercaptane?
Post by: Markov on March 05, 2009, 02:52:15 AM

My required compound is rather non-polar and does not contain acidic or basic functionality. So it should be pretty much insoluble in water (acidic as well as alkaline).

I should definitely try that out, thanks! I'll keep you posted.
Cheers!

Title: Re: practical capture of CH3SH / methanethiol / methyl mercaptane?
Post by: Markov on March 05, 2009, 05:26:12 AM

Thinking a little more about it, protonating the methanethiolate is probably what want to avoid in the first place and the reason we are looking at a Michael-type capture. For reasons of smell and toxicity of the volatile methyl mercaptan.  :-[

So I guess the Michael-type trapping will be further pursued. As an alternative to methyl acrylate, I am thinking to first look at methylmethacrylate and probably methyl crotonate and see if either of those produce significantly polymer.

Title: Re: practical capture of CH3SH / methanethiol / methyl mercaptane?
Post by: kiwi on March 06, 2009, 12:30:50 AM

considered quenching with something like MeI? thiolate anions are fairly nucleophilic, hopefully you will easily get Me2S which you can evaporate under vacuum with no trouble

Title: Re: practical capture of CH3SH / methanethiol / methyl mercaptane?
Post by: Markov on April 09, 2009, 05:12:16 AM

Quote from: kiwi on March 06, 2009, 12:30:50 AM

considered quenching with something like MeI? thiolate anions are fairly nucleophilic, hopefully you will easily get Me2S which you can evaporate under vacuum with no trouble

It turns out that we can acidify and oxidize our newly formed thioanisole (to sulfone) directly. During that treatment, methyl mercaptan gets oxidized, too.