[Sosi]

Hi!

I have the reaction between a thiol (RS-H) and hydrogen peroxide (H2O2). I want to sketch this oxidation process:

RS-H + H2O2   RS-OH + H2O

I draw the whole reaction scheme, but since I dont know how to draw it digitally, ill just explain all the steps:

RS-H + HOOH RS^- + OH⁺ + H⁺ + OH^- RS-OH + H2O

Is this correct? Thanks a lot for all the help

[tmartin]

I don't believe that RS-H --> RS- H+ in solution without some added help.  Also I would avoid thinking of H2O2 going to OH+ and OH- spontaneously.  Although if you think about the reaction in terms of nucleophilic species and electrophilic species it may help get the ball rolling for the mechanism.

[Sosi]

I gave some more thought, and I believe the mechanism should go like this:

R-S-H + H2O2 R-S-O-H + H⁺ + OH^-  (in this step, the electrons that bond sulfur to hydrogen will attack one of the oxigens of H2O2 (leaving a proton available to react), and the bond that links the two oxigens of the H2O2 will attack one of its oxigens, producing hydrogen peroxide. This will then lead to:


R-S-O-H + H⁺ + OH^- R - S - OH + H2O (in this step, the extra electrons in the hydroxyde group will attack the free proton).



Are my thoughts correct?
Thanks

[tmartin]

This time you are closer,  you have the correct nucleophile and electrophile.  Remember that sulfur (like oxygen) has lone pairs of electrons.  Those electrons can push into the O-O bond to break it and form the S-O bond.  This would leave a positive charge on sulfur and a negative charge on the displaced oxygen.

[Sosi]

This time you are closer,  you have the correct nucleophile and electrophile.  Remember that sulfur (like oxygen) has lone pairs of electrons.  Those electrons can push into the O-O bond to break it and form the S-O bond.  This would leave a positive charge on sulfur and a negative charge on the displaced oxygen.

I see! Thanks so much!

By the way, how did you write that reaction scheme? I was trying to use chemdraw, but I can't seem to find how to put the unbonded valence electrons in the atoms.
Thanks

[tmartin]

No problem.  When you're looking at the toolbar, it is the same button that allows for charges to be placed, "Chemical Symbols Tool".  It may be that I just used the notation for a carbene, but the two little dots seem to serve the same purpose regardless. 

[Sosi]

Yep!

I got it now!  I had organic chemistry too long ago and couldn't remember this kind of stuff anymore lol. Thanks once again

[orgopete]

I believe RSOH products are unstable and give RSSR + H2O as the products, but that wasn't your question.

[Sosi]

I believe RSOH products are unstable and give RSSR + H2O as the products, but that wasn't your question.

Yes, this is one of those cases. After this oxidation it will lead to the formation of a dissulfide bond OR to the overoxidation (it forms RSO₂H).