Etard Reaction: Uses, Components & Application

Instructor: Korry Barnes

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

In this lesson, our focus is going to be on a specific organic reaction known as the Etard reaction. Points of discussion will include the chemical components involved in the reaction, its uses, and its application.

That Almond Taste

Do you like the taste of almonds? Have you ever wondered where the almond-taste comes from? Obviously using real almonds is a good source of the almond-taste, but when real almonds aren't an option sometimes food chemists employ the use of an organic compound called benzaldehyde because it has an almond flavor. Actually, benzaldehyde can be extracted from real almond oil too, which explains why it has that characteristic flavor and odor.

What if the world ran out of almonds one day? How could we get our hands on benzaldehyde to quench our craving for that almond taste? Fortunately, there's an organic reaction called the Etard reaction that would be a great solution to this problem, and that's the topic of our lesson today. We will be discussing what the Etard reaction is, the chemical components involved in the reaction itself, the primary uses of the reaction, and finally some important applications of the transformation. Let's get started!

What is the Etard Reaction?

An obvious place to start our discussion would be to first define the Etard reaction. The Etard reaction is an organic transformation in which a methyl group (-CH3) bonded to an aromatic (benzene) ring undergoes an oxidation reaction and becomes an aldehyde functional group. Consider as an example the oxidation of toluene to produce benzaldehyde. The general reaction looks like:

General form of the Etard reaction

In organic chemistry, it's easy to recognize an oxidation reaction by the gain of oxygen atoms. Notice that before the reaction, the starting material doesn't contain any oxygen atoms, but the aldehyde product contains one. Oxidation!

Chemical Components of the Etard Reaction

What exactly do we need for a successful Etard reaction? In terms of the organic reactant, we've already seen that we need at least one methyl group bonded to a benzene ring. Since this is an oxidation reaction, we also need an oxidizing agent. The specific oxidizing agent the Etard reaction employs is chromyl chloride. Chromyl chloride is a chromium-based, mild oxidizing agent that is excellent at making aldehydes.

Etard reaction involving chromyl chloride as the oxidizing agent

Like most reactions, we need a solvent to run the reaction in. For the Etard reaction, the most common solvent used is carbon tetrachloride, but chloroform and carbon disulfide also work well and have been utilized.

Uses of the Etard Reaction

Ok, so now we've defined the Etard reaction, we know what reagents we need for it, let's take a look at what it can be used for. The great thing about the reaction is that it's really quite general, meaning that it can be applied to a variety of organic compounds as long as it meets the criteria. Remember, the only thing we need is a methyl group attached to an aromatic ring.

2-Methylfuran can also participate in the Etard reaction, and the product is furfural, which itself is an industrially and synthetically useful organic building block.

Etard reaction of 2-methylfuran to give furfural

Organic compounds that contain nitrogen atoms can also undergo an Etard reaction. For example, 2-methylpyridine can be taken and transformed into 2-formylpyridine easily by virtue of the Etard reaction. 2-Formylpyridine finds use in the field of organometallic chemistry (a branch of chemistry that combines organic compounds with transition metals) as well as in the pharmaceutical industry.

Etard reaction of 2-methylpyridine to give 2-formylpyridine

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