In organic chemistry, any reaction that increases the number of bonds to oxygen is referred to as an oxidation reaction. In a typical sophomore organic chemistry course, one may only see a few of the vast array of oxidizing agents. Many reagents have been developed to address specific issues while other reagents may have multiple uses. For example, potassium permanganate (KMnO4) can cause alkenes to undergo oxidative cleavage, it can oxidize alcohols, and it can convert carbons with benzylic hydrogens to carboxylic acids. To be successful, one must be able to have a strong handle on all of the capabilities of each reactant.

Let's look a list of some common oxidizing reagents used in sophomore organic chemistry to oxidize alcohols. Then, I will through a few ones that aren't typically covered. First, we need to have a look at what we are oxidizing. If you are going to oxidize a primary alcohol and you use any of the following reagents, the product will be a carboxylic acid. Oh, that brings us to another point. What is a primary alcohol?

Now that we know some different types of alcohols, we can make a general statement. Primary alcohols can be oxidized to first, an aldehyde, or they can be further oxidized to a carboxylic acid. Secondary alcohols can be oxidized only to a ketone and tertiary alcohols cannot be oxidized (there is not hydrogen on the alcohol carbon). See below.

Let's first look at some methods to oxidize a primary alcohol all the way to a carboxylic acid. In any of these reagents, the product is always the carboxylic acid and is never the aldehyde. The most commonly encountered oxidizing reagents to convert a primary alcohol are: KMnO4, CrO3, and Na2CrO2O7 (potassium permanganate, chromium trioxide, and sodium dichromate respectively). See below for an example of how each of these reagents are used.

In addition to oxidizing primary alcohols, these reagents will also oxidize secondary alcohols but only to a ketone. Ok, so what if you want to get to the aldehyde and stop? Fortunately, there are several reagents that can accomplish this goal. One of the main reagents often discussed in a typical undergraduate organic chemistry course is PCC (pyridinium chlorochromate). However, there are actually sever others that can effectively accomplish this goal as well.

Another common reagent that is used is called Dess-Martin periodinane. This reagent is extremely mild and effective for converting primary alcohols to aldehydes using a hypervalent iodine. The Dess-Martin periodinane reaction is also beneficial because the oxidation can be completed using dichloromethane as a solvent. Another common method that may not often be discussed in a typical undergraduate organic course is the Swern oxidation. This oxidizing reagent is also mild and has a wide range of functional group tolerability. The Swern oxidation uses oxalyl chloride and dimethyl sulfide (DMSO) as the main components. Finally, the last one that we will discuss is the Corey-Kim oxidation (there are still many others that can be covered! This is not an exhaustive list). The Corey-Kim oxidation has an advantage over the Swern oxidation in that it can be used at higher temperatures. On a final note, remember that all of these reagents will also oxidize a secondary alcohol to a ketone. See below for details on how each of these reagents work.

Feel free to respond to eric@thecarbondr.com. Check out the video below as an example of the powerful oxidizing power of potassium permanganate.