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Oxidation of Alcohols: Mechanism, Reaction & Conditions

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

How are alcohols oxidized and what are the products formed? In this lesson we will be learning about the mechanism behind the oxidation as well as the reaction conditions.

Not Only Used for Swimming Pools

Do you or someone you know have a swimming pool? Swimming pools can be a love-hate relationship to those that own them, they're great to enjoy on those hot summer days but they can also be a pain to keep clean and maintained. Speaking of maintenance, one of the main things a pool needs to stay clean is pool bleach, also known as sodium hypochlorite.

It actually turns out that pool bleach isn't just a good chemical for keeping swimming pools clean and tidy, it also has powerful oxidizing ability and is used for oxidizing organic compounds. In our current lesson we are going to be learning about how sodium hypochlorite can be used to oxidize organic alcohols. Specifically, our goals will be to understand how the reaction mechanism works and also look at what reaction conditions are needed for the reaction.

General Form of the Reaction and the Conditions

Let's get started by looking at what the reaction looks like and what conditions are needed. In general, an alcohol reacts with sodium hypochlorite in the presence of acetic acid to give a ketone as the final product. Since acetic acid is being used, it's important to realize that we are dealing with reaction conditions that are acidic. We will see the role of acetic acid a bit later in our discussion when we study the mechanism.

As an example let's use the oxidation of cyclohexanol as our model system. When cyclohexanol is exposed to sodium hypochlorite (NaOCl) and acetic acid an oxidation reaction takes place that gives cyclohexanone as the product. In general when a secondary alcohol (secondary because the carbon with the -OH group contains one hydrogen) is oxidized the product is always a ketone, an organic compound that contains a carbon-oxygen double bond.


Cyclohexanol is oxidized in the presence of sodium hypochlorite to give cyclohexanone
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The Mechanism Behind the Oxidation

Now that we know what sodium hypochlorite does to alcohols let's see exactly how the reaction mechanism works.

Step 1

In the first step of the reaction a molecule of acetic acid reacts with sodium hypochlorite to form hypochlorous acid, which is the active oxidizing agent for the reaction.


Acetic acid reacts with sodium hypochlorite to form hypochlorous acid
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Step 2

Now that the oxidizing agent had been formed the next step is to use it in a reaction with cyclohexanol. Cyclohexanol accepts a hydrogen atom from sodium hypochlorite and after this happens the oxygen atom contains two hydrogen atoms and a formal positive charge. The hypochlorite anion is also formed from this reaction.


Hypochlorous acid reacts with cyclohexanol in the second mechanistic step
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Step 3

In the third step of the mechanism the hypochlorite ion that was just formed attacks the carbon bonded to the oxygen atom in cyclohexanol and a water molecule gets ejected as what's called a leaving group. This is a very favorable process since when water leaves, the positive charge on oxygen is quenched and it becomes neutral again in terms of charge.


The third step of the mechanism of the oxidation of cyclohexanol
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Step 4

Here is the fourth and final step of the reaction mechanism in which the water molecule that was just ejected from cyclohexanol acts as a base and pulls off a hydrogen atom. Simultaneously the chlorine-oxygen bond breaks to finally form the ketone and our final product!


The final step in the mechanism in which water acts as a base to pull off a hydrogen atom and form the final ketone product
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It's important to notice what else is formed in the final step, namely the hydronium ion. The hydronium ion is a form of water that is VERY acidic. This further production of an acid further contributes to the acidic conditions that are associated with this oxidation reaction.

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