Reactions of Thiols - Online Tutor, Practice Problems & Exam Prep

The oxidation of thiols using an oxidizing agent like bromine water (Br₂ in water) results in the formation of disulfides. This process involves breaking the S-H bonds in two thiol molecules, leading to the creation of an S-S bond in the disulfide. Oxidation is characterized by the loss of hydrogen, while reduction involves the addition of hydrogen, converting disulfides back to thiols. Understanding these redox reactions is crucial for grasping the interconversion between thiols and disulfides in biochemical processes.

Thiol Redox Reaction Concept 1

Here we're going to say that the oxidation of a thiol with an oxidizing agent, for example, bromine water which is just Br2 in water, yields a disulfide. Now, the way it works is that we're going to have 2moles of thiol. They're going to undergo oxidation to help produce 1 mole of a disulfide. In this reaction, our SH bonds for each thiol molecule are broken and an SS bond is formed. So looking at it from an oxidation perspective, we're starting out with these 2 thiol molecules. Oxidation means the gaining of oxygen or the loss of hydrogen. So, in oxidation, we're going to lose these 2 hydrogens. The sulfurs themselves need to basically make up for the loss of a bond. So their best result is to bond with one another. Now we have these 2 sulfurs here bonded to each other. This becomes our disulfide product.

Now, going the opposite way, we could undergo reduction. And when we talk about reduction here, it means the addition of hydrogen. So in this way, we break the bond and give back hydrogens to each sulfur. Alright. So we're going to say here that oxidation shorthand is sometimes written as just O, and for reduction, we can write it in shorthand as just H. Oxidation means the gaining of oxygen or the loss of hydrogen. Reduction means the gaining of hydrogen. Alright. Now remember, reduction reactions, like we said, will convert the disulfide back into its thiol. So keep this in mind when we're talking about oxidation and reduction reactions, and how they connect thiols to disulfides.

Reactions of Thiols Example 1

Determine the product of the following oxidation reaction. So here where we have a thiol reacting with bromine water. Here remember, for us to form our disulfide, we need 2 moles of our thiol. So even though it's not shown to us, we assume there are 2 moles of this thiol. So here we have our 2 moles of our thiol. And remember what happens here is that we're going to lose a hydrogen from each thiol. So you lose H₂ here, and what's left behind connects together. So this sulfur here will connect to the other sulfur in order to make our disulfide. This would be our final answer in terms of this oxidation reaction.

Which thiol will produce the following disulfide upon oxidation?

• A.
• B.
• C.
• D.

Draw product of the following reaction.

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is the oxidation reaction of thiols?

The oxidation reaction of thiols involves converting two thiol molecules (R-SH) into a disulfide (R-S-S-R) using an oxidizing agent like bromine water (Br₂ in water). During this process, the S-H bonds in the thiol molecules are broken, and an S-S bond is formed. This reaction can be summarized as:

$2_{}R-SH+O\to R-S-S-R+2_{}HO$

Here, 'O' represents the oxidizing agent. The reaction results in the loss of hydrogen atoms (oxidation) and the formation of a disulfide bond.

How does the reduction of disulfides to thiols occur?

The reduction of disulfides to thiols involves adding hydrogen to the disulfide bond, breaking it and forming two thiol molecules. This process can be represented as:

$R-S-S-R+H\to 2_{}R-SH$

Here, 'H' represents the reducing agent. The reaction results in the addition of hydrogen atoms (reduction) and the formation of two thiol molecules from one disulfide molecule.

What are the key differences between oxidation and reduction in thiol chemistry?

In thiol chemistry, oxidation and reduction are opposite processes. Oxidation involves the loss of hydrogen atoms from thiol molecules (R-SH) and the formation of a disulfide bond (R-S-S-R). Conversely, reduction involves the addition of hydrogen atoms to a disulfide bond, breaking it and forming two thiol molecules. Oxidation can be represented as:

$2_{}R-SH+O\to R-S-S-R+2_{}HO$

Reduction can be represented as:

$R-S-S-R+H\to 2_{}R-SH$

What role does bromine water play in the oxidation of thiols?

Bromine water (Br₂ in water) acts as an oxidizing agent in the oxidation of thiols. It facilitates the conversion of two thiol molecules (R-SH) into a disulfide (R-S-S-R) by breaking the S-H bonds and forming an S-S bond. The reaction can be summarized as:

$2_{}R-SH+\mathrm{Br}{2}_{}\to R-S-S-R+2_{}H\mathrm{Br}$

Here, bromine water helps in the oxidation process by accepting the hydrogen atoms released from the thiol molecules, forming hydrobromic acid (HBr) as a byproduct.

Why is understanding redox reactions important in thiol chemistry?

Understanding redox reactions is crucial in thiol chemistry because these reactions govern the interconversion between thiols and disulfides. Oxidation reactions convert thiols (R-SH) into disulfides (R-S-S-R), while reduction reactions revert disulfides back to thiols. These processes are essential in various biochemical pathways, including protein folding and cellular redox homeostasis. By comprehending these reactions, students can better understand how thiols and disulfides function in biological systems and their roles in maintaining cellular health and function.