thiol in DMSO undergoing SN2 mechanism?

[caffeine jitters]

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hey guys,
Can anyone explain why a thiol in DMSO would take a secondary bromide through a sn2 reaction? I thought a thiol would be a weak nucleophile because it does not carry a charge. Is it sn2 simply due to the fact that the solvent is aprotic? Also, wouldn't this reaction generate a lot of H+?
Thanks for any help

 

[caffeine jitters]

So, I found the answer. I figured I would post the link here in case anyone didn't know why either.

Thiols And Thioethers — Master Organic Chemistry

The main takeaway - it is the decreased electronegativity of the sulfur atom that allows it to share its electrons more readily. Moreover, because thiols are stronger acids than alcohols, they also have weaker conjugate bases. This is why thiolates will not go through elimination reactions - they are weak bases but strong nucleophiles.

 

[doeordie]

As I like to tell my students, basicity is a thermodynamic property. Nucleophilicity is a kinetic property.

Thermodynamics dictate whether a reaction will occur.

Kinetics dictate how fast a reaction occurs.

 

[DAT Destroyer]

hey guys,
Can anyone explain why a thiol in DMSO would take a secondary bromide through a sn2 reaction? I thought a thiol would be a weak nucleophile because it does not carry a charge. Is it sn2 simply due to the fact that the solvent is aprotic? Also, wouldn't this reaction generate a lot of H+?
Thanks for any help

I will give you a great rule of thumb. When you do an SN2 reaction, we love to use a strong nucleophile. The CN- and Thiolate (mercaptide ) RS- are among the best nucleophiles in all of Organic Chemistry !!!! These nucleophiles , by Quantum Mechanic Orbital calculations show very high HOMO energies.....thus they react under what we call " orbital -controlled " reactions. They are not very good bases, which are under " charge control ", but excellent nucleophiles. How good? I have done these reactions for over 30 years.....and I have found that not even the solvent deters them !!! For example, in the SN2 reaction, we normally prefer polar aprotic solvents such as HMPT, THF, DMSO, or acetone.....When using CN- or Ch3S- nucleophiles,,,,,,,they not only went well with polar aprotic solvents, but fairly good with cheaper polar protic solvents such as ethanol !!! I discussed this anomaly with a dear friend of mine, Professor Maitland Jones, Professor Emeritus of Princeton University. He agreed that these strong nucleophiles like CN- or mercaptide.......defy logic , they react under all solvent conditions !!!! Thus, if you see one of these nucleophiles,,,,,remember.....they have high energy HOMO molecular orbitals, and react by SN2 almost all the time .


I hope this helps.

Dr. Romano