I know that purpose of molecular halogen like $\ce{Br2, Cl2}$ is to take away extra electrons on sulfur so that sulfur bridge can form. But can you use any other molecule beside halogen to do the same job, like using nucleophile like $\ce{CN-}$, tosylate etc? Why do you always see examples of halogen only?
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2$\begingroup$ Your question is based on quite a bunch of false premises. $\ce{O2}$ isn't a halogen. $\ce{CN-}$ and tosylate (and most other nucleophiles, for that matter) hardly can oxidize anything. Thiols can be oxidized by any agent with sufficient redox potential, which is by no means limited to halogens. $\endgroup$– Ivan NeretinCommented Feb 22, 2017 at 18:43
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$\begingroup$ Ok. This was a mistake. I clearly know O2 is not a halogen. Plus, my book does not have any explanation of Br2 functioning as oxidizing agent here. It just includes Br2 as examples with no explanation. Then can u explain why nucleophiles are generally not good at oxidizing anything? $\endgroup$– TLoCommented Feb 22, 2017 at 19:08
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2$\begingroup$ To oxidize something, you have to grab electrons from it. To be good at that, you have to love the electrons, i.e., to be an electrophile, which is an antonym of a nucleophile. $\endgroup$– Ivan NeretinCommented Feb 22, 2017 at 19:32
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1 Answer
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As mentioned above nucleophiles do not oxidise thiols to disulfides, what you need is an oxidising agent. Many reagents have been recorded as taking thiol to disulfide, simply stirring a thiol solution vigourously in air will give you the disulfide in some cases. It is worth noting that disulfides are relatively easily oxidised further to sulfenyl halide(RSHal), thiolsulfinate(RS(O)SR and beyond. The most reliable method of taking thiol to disulfide without over-oxidation in my experience is to reflux in inert solvent (CHCl3, DCM, THF) over activated Manganese Dioxide.
answered Feb 25, 2017 at 16:43