Sulfide Oxidation: Videos & Practice Problems

Oxidation of sulfides involves increasing the oxygen content of the molecule, leading to sulfoxides and sulfones. Sulfides, analogous to ethers but with sulfur, are more reactive due to sulfur's expanded octet. Common oxidizing agents like hydrogen peroxide and KMnO₄ convert sulfides directly to sulfones, while sodium periodate (NaIO₄) allows for partial oxidation to sulfoxides. Understanding these oxidation states and reagents is crucial for mastering sulfur chemistry.

Quick overview of oxidation.

Now we're going to explore the oxidation reactions of sulfides. So before we can talk specifically about sulfides, I think we need a little refresher on what oxidation is because it might have been a little while since you saw oxidation reduction. Just remember that oxidation is any reaction that's going to involve the increase in the oxygen content of a molecule. Now that doesn't mean that you're actually adding oxygen. It could just mean that you have more bonds to an oxygen. So this is a scheme, a little table that I use during my oxidation reduction lectures and what you should know about it is just you can see the pattern. As you move to the right, these molecules have more and more bonds to oxygen. So, if you think about it, a sulfide. What does a sulfide look like? We're going to look at it in a second, but it's a sulfur with zero oxygens on it. So as we oxidize it, we would expect that we're going to get more and more bonds to oxygen. Cool?

Reagents used to oxidize Sulfides.

One thing to keep in mind is that sulfides typically are the analog of an ether. If you look at this sulfide down here, it's basically an ether, right, except instead of having an oxygen, it has a sulfur. Ether, as we've learned in the past, if you guys have watched my ethers lectures, then what you're going to see is that ethers don't really react with anything. They're very, very difficult to make react. But sulfides are actually going to be more reactive because they have an expanded octet. Remember that the expanded octet means that they can fit up to 6 bonds with the sulfur. So it's going to give it more liberty to react with oxygen. That means that they're really going to be pretty easy to oxidize. So before we talk about the reagents, I just want to talk about how to recognize these functional groups because I know that they're new. I know we don't see them a lot. Remember that a sulfide is an ether with a sulfur. Now a sulfoxide would be once I've oxidized it, one step, I'm going to get to sulfoxide. Now sulfoxide is really the sulfur analog of a ketone. So let's say I've got my ketone. Usually, it has a carbon in the middle but I'm changing it for a sulfur. That would be a sulfoxide. So that's one way to remember it. But it turns out that the sulfoxide really could be oxidized again because sulfur can have up to 6 bonds. So if I want to oxidize it even more, I could take it all the way up to a sulfone. Now, sulfone, there really isn't anything that I can use to help you think of it because we've never really named and we haven't really been naming a lot of molecules that had 6 bonds. So it's not like I can compare it to anything from a carbon structure. But just commit it to memory, a sulfone is the most oxidized form of a sulfide. Now how do we go from one to the other? Well, it turns out that most oxidizing agents are actually going to go all the way to the sulfone. Because like I said, are sulfides easy to oxidize? Yes. So almost all oxidizing agents will take it all the way to the sulfone. Usually, we're talking about hydrogen peroxide. It's a pretty strong oxidizing agent. Also, KMnO₄ is like that famous oxidizing agent we use for a ton of things. And both of them are going to be able to take a sulfide directly to the sulfone without stopping in the middle. But what if I really want to stop, I really want to just oxidize it to a sulfoxide and not get the sulfone? Well, then we're going to use a very particular reagent. So if I use an NaIO₄, what that's going to give me is that's going to give me a partial oxidation. By the way, that's called sodium periodate. Sodium periodate. Let me just write it down so you guys can know in case you see it. Sodium periodate. So if you react sulfide with sodium periodate, what that's going to gi

Here’s what students ask on this topic:

What is sulfide oxidation and how does it differ from ether oxidation?

Sulfide oxidation involves increasing the oxygen content of a sulfide molecule, leading to the formation of sulfoxides and sulfones. Sulfides are analogous to ethers but contain sulfur instead of oxygen. Unlike ethers, which are relatively inert, sulfides are more reactive due to sulfur's expanded octet, allowing it to form up to six bonds. This makes sulfides easier to oxidize compared to ethers. Common oxidizing agents like hydrogen peroxide (H₂O₂) and potassium permanganate (KMnO₄) can convert sulfides directly to sulfones, while sodium periodate (NaIO₄) allows for partial oxidation to sulfoxides.

What are the common oxidizing agents used in sulfide oxidation?

Common oxidizing agents used in sulfide oxidation include hydrogen peroxide (H₂O₂) and potassium permanganate (KMnO₄). These agents are strong enough to convert sulfides directly to sulfones. For partial oxidation to sulfoxides, sodium periodate (NaIO₄) is used. Sodium periodate is a milder oxidizing agent that stops the oxidation process at the sulfoxide stage, preventing further oxidation to sulfone.

How does the oxidation state of sulfur change during sulfide oxidation?

During sulfide oxidation, the oxidation state of sulfur increases as it forms more bonds with oxygen. Initially, a sulfide has no oxygen atoms attached to the sulfur. Upon oxidation, it first forms a sulfoxide, where sulfur is bonded to one oxygen atom. Further oxidation leads to the formation of a sulfone, where sulfur is bonded to two oxygen atoms. The progression can be summarized as: Sulfide (R-S-R) → Sulfoxide (R-S(=O)-R) → Sulfone (R-S(=O)₂-R).

Why are sulfides more reactive than ethers in oxidation reactions?

Sulfides are more reactive than ethers in oxidation reactions due to the presence of sulfur, which has an expanded octet. This means sulfur can accommodate up to six bonds, making it more flexible and reactive compared to oxygen in ethers. The expanded octet allows sulfur to form additional bonds with oxygen during oxidation, facilitating the conversion of sulfides to sulfoxides and sulfones. This increased reactivity is why sulfides are easier to oxidize than ethers.

What is the role of sodium periodate in sulfide oxidation?

Sodium periodate (NaIO₄) plays a crucial role in sulfide oxidation by allowing for partial oxidation to sulfoxides. Unlike stronger oxidizing agents like hydrogen peroxide and potassium permanganate, which fully oxidize sulfides to sulfones, sodium periodate stops the oxidation process at the sulfoxide stage. This selective oxidation is useful when the desired product is a sulfoxide rather than a sulfone. Sodium periodate ensures that the oxidation does not proceed beyond the sulfoxide stage.